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This PDF file contains the front matter associated with SPIE Proceedings Volume 7964, including the Title Page, Copyright information, Table of Contents, Introduction, and the Conference Committee listing.
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The alignment of image-space to physical-space lies at the heart of all image-guided procedures. In intracranial
surgery, point-based registrations can be used with either skin-affixed or bone-implanted extrinsic objects called fiducial
markers. The advantages of point-based registration techniques are that they are robust, fast, and have a well developed
mathematical foundation for the assessment of registration quality. In abdominal image-guided procedures such
techniques have not been successful. It is difficult to accurately locate sufficient homologous intrinsic points in imagespace
and physical-space, and the implantation of extrinsic fiducial markers would constitute "surgery before the
surgery." Image-space to physical-space registration for abdominal organs has therefore been dominated by surfacebased
registration techniques which are iterative, prone to local minima, sensitive to initial pose, and sensitive to
percentage coverage of the physical surface.
In our work in image-guided kidney surgery we have developed a composite approach using "virtual fiducials."
In an open kidney surgery, the perirenal fat is removed and the surface of the kidney is dotted using a surgical marker. A
laser range scanner (LRS) is used to obtain a surface representation and matching high definition photograph. A surface
to surface registration is performed using a modified iterative closest point (ICP) algorithm. The dots are extracted from
the high definition image and assigned the three dimensional values from the LRS pixels over which they lie. As the
surgery proceeds, we can then use point-based registrations to re-register the spaces and track deformations due to
vascular clamping and surgical tractions.
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Off-pump, intracardiac, beating heart surgery has the potential to improve patient outcomes by eliminating the need for
cardiopulmonary bypass and aortic cross clamping but it requires extensive image guidance as well as the development
of specialized instrumentation. Previously, developments in image guidance and instrumentation were validated on
either a static phantom or in vivo through porcine models. This paper describes the design and development of a surgical
phantom for simulating off-pump mitral valve replacement inside the closed beating heart. The phantom allows surgical
access to the mitral annulus while mimicking the pressure inside the beating heart. An image guidance system using
tracked ultrasound, magnetic instrument tracking and preoperative models previously developed for off-pump mitral
valve replacement is applied to the phantom. Pressure measurements and ultrasound images confirm the phantom closely
mimics conditions inside the beating heart.
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The ability to perform fast, accurate, deformable registration with intraoperative images featuring surgical excisions was
investigated for use in cone-beam CT (CBCT) guided head and neck surgery. Existing deformable registration methods
generally fail to account for tissue excised between image acquisitions and typically simply "move" voxels within the
images with no ability to account for tissue that is removed (or introduced) between scans. We have thus developed an
approach in which an extra dimension is added during the registration process to act as a sink for voxels removed during
the course of the procedure. A series of cadaveric images acquired using a prototype CBCT-capable C-arm were used to
model tissue deformation and excision occurring during a surgical procedure, and the ability of deformable registration
to correctly account for anatomical changes under these conditions was investigated. Using a previously developed
version of the Demons deformable registration algorithm, we identify the difficulties that traditional registration
algorithms encounter when faced with excised tissue and present a modified version of the algorithm better suited for
use in intraoperative image-guided procedures. Studies were performed for different deformation and tissue excision
tasks, and registration performance was quantified in terms of the ability to accurately account for tissue excision while
avoiding spurious deformations arising around the excision.
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Intraoperative surface imaging with navigated beta-probes has been shown to be a possibility to enable
control of tumor resection borders. By employing ad hoc models of the detection physics the image
quality can be improved. Our model computes the amount of radiation from a single point source that
reaches the detector, with the solid angle subtended by the detector on the source, assuming perfect
shielding. The sensitivity of the detector to the source due to the angle between the detector axis and
the source-to-detector vector is also considered. A set of experiments was performed with three sources
(two 10x10mm2 and one 20x10mm2 pieces of cellulose saturated with FDG) on a plate as phantom.
Five sets of measurements were taken, three of them at a distance of 10mm from the plate und two
at 30mm. At both distances one measurement set was taken in a random manner and the other ones
systematically covering the whole area. The same experiments were simulated with our model and
the GATE simulation framework. The resulting measurements from the experiments and simulations
were then used to perform a reconstruction of the sources. The real measurements were compared to
those simulated with our model and GATE, with a mean NCC of 80.64% for our model and 70.14% for
GATE. In the reconstructions of the real measurements the sources were visually quite well separated,
however the reconstructions of the measurements simulated by the model show that there is still room
for further improvement.
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Microwave ablation is a promising option in lung cancer therapy. However, it's rarely used in percutaneous lung cancer
therapy compared to liver cancer, because the presence of a large amount of air within the lung creates significant back
shadowing artifacts that preclude adequate delineation of anatomic details on sonography. To utilize microwave ablation
in malignant lung tumor therapy, we developed a novel percutaneous intervention surgery navigation system (CAINS-I),
which capitalizes on using computer assisted technology to help lung cancer patients whose condition are not amenable
to surgical resection, sonographic guidance and intraoperative CT surgery. In these surgeries, preoperative CT images
with patient respiration state are first acquired, which are then visualized using GPU-accelerated volume rendering. The
optimal surgery trajectories are then planned based on 3D thermal field computation and surgery simulation in the
surgery planning software. During the surgery, the patient breath is control by a portable volume ventilator system which
could limit the movement and displacement of the tumor. Then the microwave probe is punctured into the tumor
according to the dynamic respiratory state and the tumor is ablated by microwave energy. After the surgery,
postoperative CT are acquired and compared to the preoperative CT, and the surgery is evaluated by compare
preoperative and postoperative CT images. The development of this technique represented an advance from the
traditional ways for lung cancer therapy and significantly extends the indications of microwave ablation.
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While several mosaicking algorithms have been developed to compose endoscopic images of the internal urinary
bladder wall into panoramic images, the quantitative evaluation of these output images in terms of
geometrical distortions have often not been discussed. However, the visualization of the distortion level is
highly desired for an objective image-based medical diagnosis. Thus, we present in this paper a method to
create quality maps from the characteristics of transformation parameters, which were applied to the endoscopic
images during the registration process of the mosaicking algorithm. For a global first view impression,
the quality maps are laid over the panoramic image and highlight image regions in pseudo-colors according
to their local distortions. This illustration supports then surgeons to identify geometrically distorted structures
easily in the panoramic image, which allow more objective medical interpretations of tumor tissue in
shape and size. Aside from introducing quality maps in 2-D, we also discuss a visualization method to map
panoramic images onto a 3-D spherical bladder model. Reference points are manually selected by the surgeon
in the panoramic image and the 3-D model. Then the panoramic image is mapped by the Hammer-Aitoff
equal-area projection onto the 3-D surface using texture mapping. Finally the textured bladder model can
be freely moved in a virtual environment for inspection. Using a two-hemisphere bladder representation,
references between panoramic image regions and their corresponding space coordinates within the bladder
model are reconstructed. This additional spatial 3-D information thus assists the surgeon in navigation,
documentation, as well as surgical planning.
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The localization of brachytherapy seeds in relation to the prostate is a key step in intraoperative treatment planning (ITP)
for improving outcomes in prostate cancer patients treated with low dose rate prostate brachytherapy. Transrectal
ultrasound (TRUS) has traditionally been the modality of choice to guide the prostate brachytherapy procedure due to its
relatively low cost and apparent ease of use. However, TRUS is unable to visualize seeds well, precluding ITP and
producing suboptimal results. While other modalities such as X-ray and magnetic resonance imaging have been
investigated to localize seeds in relation to the prostate, photoacoustic imaging has become an emerging and promising
modality to solve this challenge. Moreover, photoacoustic imaging may be more practical in the clinical setting
compared to other methods since it adds little additional equipment to the ultrasound system already adopted in
procedure today, reducing cost and simplifying engineering steps. In this paper, we demonstrate the latest efforts of
localizing prostate brachytherapy seeds using photoacoustic imaging, including visualization of multiple seeds in actual
prostate tissue. Although there are still several challenges to be met before photoacoustic imaging can be used in the
operating room, we are pleased to present the current progress in this effort.
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Planned in-situ radiosensitization may improve the therapeutic ratio of image guided 125I prostate brachytherapy.
Spacers used in permanent implants may be manufactured from a radiosensitizer-releasing polymer to deliver protracted
localized sensitization of the prostate. Such devices will have a limited drug-loading capacity, and the drug release
schedule that optimizes outcome, under such a constraint, is not known. This work determines the optimal elution
schedules for 125I prostate brachytherapy. The interaction between brachytherapy dose distributions and drug
distribution around drug eluting spacers is modeled using a linear-quadratic (LQ) model of cell kill. Clinical
brachytherapy plans were used to calculate the biologic effective dose (BED) for planned radiation dose distributions
while adding the spatial distributions of radiosensitizer while varying the temporal release schedule subject to a
constraint on the drug capacity of the eluting spacers. Results: The greatest increase in BED is achieved by schedules
with the greatest sensitization early in the implant. Making brachytherapy spacers from radiosensitizer eluting polymer
transforms inert parts of the implant process into a means of enhancing the effect of the brachytherapy radiation. Such
an approach may increase the therapeutic ratio of prostate brachytherapy or offer a means of locally boosting the
radiation effect without increasing the radiation dose to surrounding tissues.
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To make Quantitative Radiology (QR) a reality in routine clinical practice, computerized automatic anatomy recognition
(AAR) becomes essential. As part of this larger goal, we present in this paper a novel fuzzy strategy for building bodywide
group-wise anatomic models. They have the potential to handle uncertainties and variability in anatomy naturally
and to be integrated with the fuzzy connectedness framework for image segmentation. Our approach is to build a family
of models, called the Virtual Quantitative Human, representing normal adult subjects at a chosen resolution of the
population variables (gender, age). Models are represented hierarchically, the descendents representing organs contained
in parent organs. Based on an index of fuzziness of the models, 32 thorax data sets, and 10 organs defined in them, we
found that the hierarchical approach to modeling can effectively handle the non-linear relationships in position, scale,
and orientation that exist among organs in different patients.
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The problem of extrapolating cost-effective relevant information from distinctly finite or sparse data, while balancing the
competing goals between workflow and engineering design, and between application and accuracy is the 'sparse data
extrapolation problem'. Within the context of open abdominal image-guided liver surgery, one realization of this
problem is compensating for non-rigid organ deformations while maintaining workflow for the surgeon. More
specifically, rigid organ-based surface registration between CT-rendered liver surfaces and laser-range scanned
intraoperative partial surface counterparts resulted in an average closest-point residual 6.1 ± 4.5 mm with maximumsigned
distances ranging from -13.4 to 16.2 mm. Similar to the neurosurgical environment, there is a need to correct for
soft tissue deformation to translate image-guided interventions to the abdomen (e.g. liver, kidney, pancreas, etc.). While
intraoperative tomographic imaging is available, these approaches are less than optimal solutions to the sparse data
extrapolation problem. In this paper, we compare and contrast three sparse data extrapolation methods to that of datarich
interpolation for the correction of deformation within a liver phantom containing 43 subsurface targets. The
findings indicate that the subtleties in the initial alignment pose following rigid registration can affect correction up to 5-
10%. The best deformation compensation achieved was approximately 54.5% (target registration error of 2.0 ± 1.6 mm)
while the data-rich interpolative method was 77.8% (target registration error of 0.6 ± 0.5 mm).
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Needle insertion planning for digital breast tomosynthesis (DBT) guided biopsy has the potential to improve patient
comfort and intervention safety. However, a relevant planning should take into account breast tissue deformation and
lesion displacement during the procedure. Deformable models, like finite elements, use the elastic characteristics of the
breast to evaluate the deformation of tissue during needle insertion. This paper presents a novel approach to locally
estimate the Young's modulus of the breast tissue directly from the DBT data. The method consists in computing the
fibroglandular percentage in each of the acquired DBT projection images, then reconstructing the density volume.
Finally, this density information is used to compute the mechanical parameters for each finite element of the deformable
mesh, obtaining a heterogeneous DBT based breast model. Preliminary experiments were performed to evaluate the
relevance of this method for needle path planning in DBT guided biopsy. The results show that the heterogeneous DBT
based breast model improves needle insertion simulation accuracy in 71% of the cases, compared to a homogeneous
model or a binary fat/fibroglandular tissue model.
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1- or 2-directional MRI blood flow mapping sequences are an integral part of standard MR protocols for diagnosis
and therapy control in heart diseases. Recent progress in rapid MRI has made it possible to acquire
volumetric, 3-directional cine images in reasonable scan time. In addition to flow and velocity measurements
relative to arbitrarily oriented image planes, the analysis of 3-dimensional trajectories enables the visualization
of flow patterns, local features of flow trajectories or possible paths into specific regions. The anatomical and
functional information allows for advanced hemodynamic analysis in different application areas like stroke risk
assessment, congenital and acquired heart disease, aneurysms or abdominal collaterals and cranial blood flow.
The complexity of the 4D MRI flow datasets and the flow related image analysis tasks makes the development of
fast comprehensive data exploration software for advanced flow analysis a challenging task. Most existing tools
address only individual aspects of the analysis pipeline such as pre-processing, quantification or visualization, or
are difficult to use for clinicians. The goal of the presented work is to provide a software solution that supports
the whole image analysis pipeline and enables data exploration with fast intuitive interaction and visualization
methods. The implemented methods facilitate the segmentation and inspection of different vascular systems.
Arbitrary 2- or 3-dimensional regions for quantitative analysis and particle tracing can be defined interactively.
Synchronized views of animated 3D path lines, 2D velocity or flow overlays and flow curves offer a detailed insight
into local hemodynamics. The application of the analysis pipeline is shown for 6 cases from clinical practice,
illustrating the usefulness for different clinical questions. Initial user tests show that the software is intuitive to
learn and even inexperienced users achieve good results within reasonable processing times.
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There are commercial products which provide 3D rendered volumes, reconstructed from electro-anatomical mapping
and/or pre-operative CT/MR images of a patient's heart with tools for highlighting target locations for
cardiac ablation applications. However, it is not possible to update the three-dimensional (3D) volume intraoperatively
to provide the interventional cardiologist with more up-to-date feedback at each instant of time. In
this paper, we describe the system we have developed for real-time three-dimensional stereo visualization for
cardiac ablation. A 4D ultrasound probe is used to acquire and update a 3D image volume. A magnetic tracking
device is used to track the distal part of the ablation catheter in real time and a master-slave robot-assisted system
is developed for actuation of a steerable catheter. Three-dimensional ultrasound image volumes go through some
processing to make the heart tissue and the catheter more visible. The rendered volume is shown in a virtual
environment. The catheter can also be added as a virtual tool to this environment to achieve a higher update
rate on the catheter's position. The ultrasound probe is also equipped with an EM tracker which is used for
online registration of the ultrasound images and the catheter tracking data. The whole augmented reality scene
can be shown stereoscopically to enhance depth perception for the user. We have used transthoracic echocardiography
(TTE) instead of the conventional transoesophageal (TEE) or intracardiac (ICE) echocardiogram. A
beating heart model has been used to perform the experiments. This method can be used both for diagnostic
and therapeutic applications as well as training interventional cardiologists.
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We present a novel view on 2D/3D image registration by introducing a generic algorithmic framework that is
based on supervised machine learning (SML). First and foremost, this class of algorithms, referred to as texture
model registration (TMR), aims at making 2D/3D registration applicable for time-critical image guided medical
procedures. TMR methods are two-stage. In a first offline pre-computational stage, a prediction rule is derived
from a pre-interventional 3D image and according geometric constraints. This is achieved by computing digitally
reconstructed radiographs, pre-processing them, extracting their texture, and applying SML methods. In a
second online stage, the inferred rule is used for predicting the spatial rigid transformation of unseen intrainterventional
2D images. A first simple concrete TMR implementation, referred to as TMR-PCR, is introduced.
This approach involves principal component regression (PCR) and simple intermediate pre-processing steps.
Using TMR-PCR, first experimental results on five clinical IGRT 3D data sets and synthetic intra-interventional
images are presented. The implementation showed an average registration rate of 48 Hz over 40000 registrations,
and succeeded in the majority of cases with a mean target registration error smaller than 2 mm. Finally, the
potential and characteristics of the proposed methodical framework are discussed.
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A successful image-guided surgical intervention requires accurate measurement of coordinate systems. Uncertainty is
introduced every time a pose is measured by the optical tracking system. When we transform a measured pose into a
different coordinate system, the covariance (which encodes the uncertainty of the pose) must be propagated to this new
coordinate system. In this paper, we describe a method for propagating covariances estimated from registration, tracking,
and instrument calibration into the tip of the surgical tool. This is clinically important, since it is at the tool tip that the
clinician cares about uncertainty. We demonstrate that the propagation method, which is computed in real time as the tool
moves through space, reliably computes the propagated covariance by comparing our estimate to true covariances from
Monte Carlo simulations.
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Previous studies have shown that bronchoscopy guidance systems improve accuracy and reduce skill variation
among physicians during bronchoscopy. In the past, we presented an image-based bronchoscopy guidance system
that has been extensively validated in live bronchoscopic procedures. However, this system cannot actively recover
from adverse events, such as patient coughing or dynamic airway collapses. After such events, the bronchoscope
position is recovered only by moving back to a previously seen and easily identifiable bifurcation such as the main
carina. Furthermore, the system requires an attending technician to closely follow the physician's movement of
the bronchoscope to avoid misguidance. Also, when the physician is forced to advance the bronchoscope across
multiple bifurcations, the system is not able to detect faulty maneuvers. We propose two system-level solutions.
The first solution is a system-level guidance strategy that incorporates a global-registration algorithm to provide
the physician with updated navigational and guidance information during bronchoscopy. The system can handle
general navigation to a region of interest (ROI), as well as adverse events, and it requires minimal commands so
that it can be directly controlled by the physician. The second solution visualizes the global picture of all the
bifurcations and their relative orientations in advance and suggests the maneuvers needed by the bronchoscope
to approach the ROI. Guided bronchoscopy results using human airway-tree phantoms demonstrate the potential
of the two solutions.
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Registration of endoscopic video to preoperative CT facilitates high-precision surgery of the head, neck, and skull-base. Conventional video-CT registration is limited by the accuracy of the tracker and does not use the underlying video or CT image data. A new image-based video registration method has been developed to overcome the limitations of conventional tracker-based registration. This method adds to a navigation system based on intraoperative C-arm cone-beam CT (CBCT), in turn providing high-accuracy registration of video to the surgical scene. The resulting registration enables visualization of the CBCT and planning data within the endoscopic video. The system incorporates a mobile C-arm, integrated with an optical tracking system, video endoscopy, deformable registration of preoperative CT with intraoperative CBCT, and 3D visualization. Similarly to tracker-based approach, the image-based video-CBCT registration the endoscope is localized with optical tracking system followed by a direct 3D image-based registration of the video to the CBCT. In this way, the system achieves video-CBCT registration that is both fast and accurate. Application in skull-base surgery demonstrates overlay of critical structures (e.g., carotid arteries) and surgical targets with sub-mm accuracy. Phantom and cadaver experiments show consistent improvement of target registration error (TRE) in video overlay over conventional tracker-based registration-e.g., 0.92mm versus 1.82mm for image-based and tracker-based registration, respectively. The proposed method represents a two-fold advance-first, through registration of video to up-to-date intraoperative CBCT, and second, through direct 3D image-based video-CBCT registration, which together provide more confident visualization of target and normal tissues within up-to-date images.
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We propose a novel neuro-fuzzy hybrid transformation model for deformable image registration in intra-operative image
guided procedures involving large soft tissue deformation. The hybrid model consists of two parts: a physics-based
model and a mathematical approximation model. The physics-based model is based on elastic solid mechanics to model
major deformation patterns of the central part of organs, and the mathematical approximation model depicts the
deformation of the residual part along organ boundary. A neuro-fuzzy technique is employed to seamlessly integrate the
two parts into a unified hybrid model. Its unique feature is to incorporate domain knowledge of soft tissue deformation
patterns and significantly reduce the number of transformation parameters. We demonstrate the effectiveness of our
hybrid model to register liver magnetic resonance (MR) images in human subject study. This technique has the potential
to significantly improve intra-operative image guidance in abdominal and thoracic procedures.
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Congenital heart defect (CHD) is the most common birth defect and a frequent cause of death for children.
Tetralogy of Fallot (ToF) is the most often occurring CHD which affects in particular the pulmonary valve and
trunk. Emerging interventional methods enable percutaneous pulmonary valve implantation, which constitute
an alternative to open heart surgery. While minimal invasive methods become common practice, imaging and
non-invasive assessment tools become crucial components in the clinical setting. Cardiac computed tomography
(CT) and cardiac magnetic resonance imaging (cMRI) are techniques with complementary properties and ability
to acquire multiple non-invasive and accurate scans required for advance evaluation and therapy planning. In
contrary to CT which covers the full 4D information over the cardiac cycle, cMRI often acquires partial information,
for example only one 3D scan of the whole heart in the end-diastolic phase and two 2D planes (long and
short axes) over the whole cardiac cycle. The data acquired in this way is called sparse cMRI. In this paper, we
propose a regression-based approach for the reconstruction of the full 4D pulmonary trunk model from sparse
MRI. The reconstruction approach is based on learning a distance function between the sparse MRI which needs
to be completed and the 4D CT data with the full information used as the training set. The distance is based
on the intrinsic Random Forest similarity which is learnt for the corresponding regression problem of predicting
coordinates of unseen mesh points. Extensive experiments performed on 80 cardiac CT and MR sequences
demonstrated the average speed of 10 seconds and accuracy of 0.1053mm mean absolute error for the proposed
approach. Using the case retrieval workflow and local nearest neighbour regression with the learnt distance function
appears to be competitive with respect to "black box" regression with immediate prediction of coordinates,
while providing transparency to the predictions made.
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Bronchoscopy-guidance systems have been shown to improve the success rate of bronchoscopic procedures. A key
technical cornerstone of bronchoscopy-guidance systems is the synchronization between the virtual world, derived
from a patient's three-dimensional (3D) multidetector computed-tomography (MDCT) scan, and the real world,
derived from the bronchoscope video during a live procedure. Two main approaches for synchronizing these worlds
exist: electromagnetic navigation bronchoscopy (ENB) and image-based bronchoscopy. ENB systems require
considerable extra hardware, and both approaches have drawbacks that hinder continuous robust guidance. In
addition, they both require an attending technician to be present. We propose a technician-free strategy that
enables real-time guidance of bronchoscopy. The approach uses measurements of the bronchoscope's movement to
predict its position in 3D virtual space. To achieve this, a bronchoscope model, defining the device's shape in the
airway tree to a given point p, provides an insertion depth to p. In real time, our strategy compares an observed
bronchoscope insertion depth and roll angle, measured by an optical sensor, to precalculated insertion depths
along a predefined route in the virtual airway tree. This leads to a prediction of the bronchoscope's location and
orientation. To test the method, experiments involving a PVC-pipe phantom and a human airway-tree phantom
verified the bronchoscope models and the entire method, respectively. The method has considerable potential
for improving guidance robustness and simplicity over other bronchoscopy-guidance systems.
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Airway wall remodeling in asthma and chronic obstructive pulmonary disease (COPD) is a well-known indicator
of the pathology. In this context, current clinical studies aim for establishing the relationship between the
airway morphological structure and its function. Multislice computed tomography (MSCT) allows morphometric
assessment of airways, but requires dedicated segmentation tools for clinical exploitation. While most of the
existing tools are limited to cross-section measurements, this paper develops a fully 3D approach for airway wall
segmentation. Such approach relies on a deformable model which is built up as a patient-specific surface model
at the level of the airway lumen and deformed to reach the outer surface of the airway wall. The deformation
dynamics obey a force equilibrium in a Lagrangian framework constrained by a vector field which avoids model
self-intersections. The segmentation result allows a dense quantitative investigation of the airway wall thickness
with a deeper insight at bronchus subdivisions than classic cross-section methods. The developed approach has
been assessed both by visual inspection of 2D cross-sections, performed by two experienced radiologists on clinical
data obtained with various protocols, and by using a simulated ground truth (pulmonary CT image model). The
results confirmed a robust segmentation in intra-pulmonary regions with an error in the range of the MSCT
image resolution and underlined the interest of the volumetric approach versus purely 2D methods.
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Transbronchial needle aspiration (TBNA) is a common procedure to collect tissue samples from the inside of the lung for diagnostic use. However, the main drawback of the procedure is that it has to be blindly performed because the biopsy target region is behind the bronchial wall and hence not within the field of view of the bronchoscope. Thus, the diagnostic yield rate is low. To increase success rate of TBNA biopsy an electromagnetic trackable TBNA needle has been introduced. Nevertheless, the introduced prototype TBNA instrument was evaluated in a rigid rubber phantom without taking respiratory motion into account. The purpose of this study is to present a new TBNA needle where the electromagnetic sensor is directly integrated into a TBNA needle and to access its performance in a regularly ventilated lung. Using our previously presented navigation system, seven TBNA interventions were performed in a porcine lung during regular respiration lung movement; respectively a control computer tomography scan was acquired. We evaluated tracking accuracy of the electromagnetically tracked needle during the entire respiratory cycle for each intervention. The newly developed TBNA needle successfully operated throughout all seven interventions. According to the results, our electromagnetic TBNA tracking system is a promising approach to increase the TBNA biopsy success rate.
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This paper presents an improved bronchoscope tracking method for bronchoscopic navigation using scale invariant
features and sequential Monte Carlo sampling. Although image-based methods are widely discussed in
the community of bronchoscope tracking, they are still limited to characteristic information such as bronchial
bifurcations or folds and cannot automatically resume the tracking procedure after failures, which result usually
from problematic bronchoscopic video frames or airway deformation. To overcome these problems, we propose
a new approach that integrates scale invariant feature-based camera motion estimation into sequential Monte
Carlo sampling to achieve an accurate and robust tracking. In our approach, sequential Monte Carlo sampling
is employed to recursively estimate the posterior probability densities of the bronchoscope camera motion parameters
according to the observation model based on scale invariant feature-based camera motion recovery. We
evaluate our proposed method on patient datasets. Experimental results illustrate that our proposed method
can track a bronchoscope more accurate and robust than current state-of-the-art method, particularly increasing
the tracking performance by 38.7% without using an additional position sensor.
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Purpose: Ultrasound (US) elevation beamwidth causes a certain type of image artifact around the anechoic
areas of the tissue. It is generally assumed that the US image is of zero thickness, which contradicts the
fact that the acoustic beam can only be mechanically focused at a depth resulting in a finite, non-uniformed
elevation beamwidth. We suspect that elevation beamwidth artifacts contribute to target reconstruction error
in computer-assisted interventions. This paper introduces a method for characterization of the beamwidth for
transrectal ultrasound (TRUS) used in prostate brachythyerapy. In particular, we measure how the US sectionthickness
varies along the beam's axial depth. Method: We developed a beam-profiling device (a TRUS-bridge
phantom) specifically tailored for standard brachytherapy ultrasound imaging systems to generate a complete
section-thickness profile of a given TRUS transducer. The device was designed in CAD software and prototyped
by a 3D printer. Result: The experimental results demonstrated that the TRUS beam in the elevation direction
is focused closely to the transducer and theoretically the transducer would provide a better elevational resolution
within that range. Conclusion: We presented a beam profiling phantom to measure the section-thickness of a
transrectal ultrasound transducer for operating room use. However, there are some limitations which need to
be addressed, for example, phantom sterilization and the speed of sound in the current medium of experiment
which is not the same as that of biological tissues.
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We apply the initial momentum shape representation of diffeomorphic metric mapping from a template region of interest
(ROI) to a given ROI as a morphometic marker in Parkinson's disease. We used a three-step segmentation-registrationmomentum
process to derive feature vectors from ROIs in a group of 42 subjects consisting of 19 Parkinson's Disease
(PD) subjects and 23 normal control (NC) subjects. Significant group differences between PD and NC subjects were
detected in four basal ganglia structures including the caudate, putamen, thalamus and globus pallidus. The magnitude of
regionally significant between-group differences detected ranged between 34-75%. Visualization of the different
structural deformation pattern between-groups revealed that some parts of basal ganglia structure actually hypertrophy,
presumably as a compensatory response to more widespread atrophy. Our results of both hypertrophy and atrophy in the
same structures further demonstrate the importance of morphological measures as opposed to overall volume in the
assessment of neurodegenerative disease.
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A number of groups have reported on the occurrence of intra-operative brain shift during deep brain stimulation (DBS)
surgery. This has a number of implications for the procedure including an increased chance of intra-cranial bleeding and
complications due to the need for more exploratory electrodes to account for the brain shift. It has been reported that the
amount of pneumocephalus or air invasion into the cranial cavity due to the opening of the dura correlates with intraoperative
brain shift. Therefore, pre-operatively predicting the amount of pneumocephalus expected during surgery is of
interest toward accounting for brain shift. In this study, we used 64 DBS patients who received bilateral electrode
implantations and had a post-operative CT scan acquired immediately after surgery (CT-PI). For each patient, the
volumes of the pneumocephalus, left ventricle, right ventricle, third ventricle, white matter, grey matter, and cerebral
spinal fluid were calculated. The pneumocephalus was calculated from the CT-PI utilizing a region growing technique
that was initialized with an atlas-based image registration method. A multi-atlas-based image segmentation method was
used to segment out the ventricles of each patient. The Statistical Parametric Mapping (SPM) software package was
utilized to calculate the volumes of the cerebral spinal fluid (CSF), white matter and grey matter. The volume of
individual structures had a moderate correlation with pneumocephalus. Utilizing a multi-linear regression between the
volume of the pneumocephalus and the statistically relevant individual structures a Pearson's coefficient of r = 0.4123 (p
= 0.0103) was found. This study shows preliminary results that could be used to develop a method to predict the amount
of pneumocephalus ahead of the surgery.
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Preoperative magnetic resonance images are typically used for neuronavigation in image-guided neurosurgery. However,
intraoperative brain deformation (e.g., as a result of gravitation, loss of cerebrospinal fluid, retraction, resection, etc.)
significantly degrades the accuracy in image guidance, and must be compensated for in order to maintain sufficient
accuracy for navigation. Biomechanical finite element models are effective techniques that assimilate intraoperative data
and compute whole-brain deformation from which to generate model-updated MR images (uMR) to improve accuracy in
intraoperative guidance. To date, most studies have focused on early surgical stages (i.e., after craniotomy and
durotomy), whereas simulation of more complex events at later surgical stages has remained to be a challenge using
biomechanical models. We have developed a method to simulate partial or complete tumor resection that incorporates
intraoperative volumetric ultrasound (US) and stereovision (SV), and the resulting whole-brain deformation was used to
generate uMR. The 3D ultrasound and stereovision systems are complimentary to each other because they capture
features deeper in the brain beneath the craniotomy and at the exposed cortical surface, respectively. In this paper, we
illustrate the application of the proposed method to simulate brain tumor resection at three temporally distinct surgical
stages throughout a clinical surgery case using sparse displacement data obtained from both the US and SV systems. We
demonstrate that our technique is feasible to produce uMR that agrees well with intraoperative US and SV images after
dural opening, after partial tumor resection, and after complete tumor resection. Currently, the computational cost to
simulate tumor resection can be up to 30 min because of the need for re-meshing and the trial-and-error approach to
refine the amount of tissue resection. However, this approach introduces minimal interruption to the surgical workflow,
which suggests the potential for its clinical application with further improvement in computational efficiency.
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Compensating for brain shift as surgery progresses is important to ensure sufficient accuracy in patient-to-image
registration in the operating room (OR) for reliable neuronavigation. Ultrasound has emerged as an important and
practical imaging technique for brain shift compensation either by itself or through computational modeling that
estimates whole-brain deformation. Using volumetric true 3D ultrasound (3DUS), it is possible to nonrigidly (e.g., based
on B-splines) register two temporally different 3DUS images directly to generate feature displacement maps for data
assimilation in the biomechanical model. Because of a large amount of data and number of degrees-of-freedom (DOFs)
involved, however, a significant computational cost may be required that can adversely influence the clinical feasibility
of the technique for efficiently generating model-updated MR (uMR) in the OR. This paper parametrically investigates
three B-splines registration parameters and their influence on the computational cost and registration accuracy: number
of grid nodes along each direction, floating image volume down-sampling rate, and number of iterations. A simulated
rigid body displacement field was employed as a ground-truth against which the accuracy of displacements generated
from the B-splines nonrigid registration was compared. A set of optimal parameters was then determined empirically that
result in a registration computational cost of less than 1 min and a sub-millimetric accuracy in displacement
measurement. These resulting parameters were further applied to a clinical surgery case to demonstrate their practical
use. Our results indicate that the optimal set of parameters result in sufficient accuracy and computational efficiency in
model computation, which is important for future application of the overall biomechanical modeling to generate uMR for
image-guidance in the OR.
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Recent work from our group has shown the primacy of the bifurcation area ratio and tortuosity in determining the
amount of disturbed flow at the carotid bifurcation, believed to be a local risk factor for the carotid atherosclerosis. We
have also presented fast and reliable methods of extraction of geometry from routine 3D contrast-enhanced magnetic
resonance angiography, as the necessary step along the way for large-scale trials of such local risk factors. In the present
study, we refine our original geometric variables to better reflect the underlying fluid mechanical principles. Flaring of
the bifurcation, leading to flow separation, is defined by the maximum relative expansion of the common carotid artery
(CCA), proximal to the bifurcation apex. The beneficial effect of curvature on flow inertia, via its suppression of flow
separation, is now characterized by the tortuosity of CCA as it enters the flare region. Based on data from 50 normal
carotid bifurcations, multiple linear regressions of these new independent geometric predictors against the dependent
disturbed flow burden reveals adjusted R2 values approaching 0.5, better than the values closer to 0.3 achieved using the
original variables. The excellent scan-rescan reproducibility demonstrated for our earlier geometric variables is shown to
be preserved for the new definitions. Improved prediction of disturbed flow by robust and reproducible vascular
geometry offers a practical pathway to large-scale studies of local risk factors in atherosclerosis.
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Diagnosis and treatment decisions of cerebrovascular diseases are currently based on structural information like
the endovascular lumen. In future, clinical diagnosis will increasingly be based on functional information which
gives direct information about the physiological parameters and, hence, is a direct measure for the severity of
the pathology. In this context, an important functional quantity is the volumetric blood flow over time. The
proposed flow quantification method uses contrasted X-ray images from cerebrovascular interventions and a
model of contrast agent dispersion to estimate the flow parameters from the spatial and temporal development
of the contrast agent concentration through the vascular system.
To evaluate the model-based blood flow quantification under realistic circumstances, dedicated cerebrovascular
data has been acquired during clinical interventions. To this aim, a clinical protocol for this novel procedure
has been defined and optimized. For the verification of the measured flow results ultrasound Doppler measurements
have been performed acting as reference measurements.
The clinical data available so far indicates the ability of the proposed flow model to explain the in-vivo
transport of contrast agent in blood. The flow quantification results show good correspondence of flow waveform
and mean volumetric flow rate with the accomplished ultrasound measurements before or after angiography.
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We propose a system to estimate blood flow velocity in angiographic image data for patient-specific blood
flow simulations. Angiographies are acquired routinely for diagnosis and before treatment of vascular diseases.
Projective blood flow is measured in digital subtraction X-ray angiography (2D-DSA) images by tracking contrast
agent propagation. Spatial information is added by re-projecting 2D centerline pixels to the reconstructed 3D
X-ray rotation angiography (3D-RA) data of the same subject. Ambiguities caused by occluding vessels from
the virtual viewpoint of the acquired 2D-DSA image are resolved by a graph-based approach. The blood flow
velocity can be used as boundary condition for exact blood flow simulations that can help physicians to understand
hemodynamics of the vasculature. Our focus is to analyze cerebral angiographic data. We performed several
experiments with phantom and patient data that proved the accuracy and the functionality of our method. We
evaluated experimentally the projective flow estimation method and the re-projection method. We measured
mean deviations to the ground truth between 11 % and 15.7 % for phantom data. We also showed the ability of
our method to produce plausible results with patient-data.
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Presentation of detailed anatomical structures via 3-D models helps navigation and deployment of the prosthetic valve in
TAVI procedures. Fast and automatic contrast detection in the aortic root on X-ray images facilitates a seamless
workflow to utilize the 3-D models by triggering 2-D/3-D registration automatically when motion compensation is
needed. In this paper, we propose a novel method for automatic detection of contrast injection in the aortic root on
fluoroscopic and angiographic sequences. The proposed method is based on histogram analysis and likelihood ratio test,
and is robust to variations in the background, the density and volume of the injected contrast, and the size of the aorta.
The performance of the proposed algorithm was evaluated on 26 sequences from 5 patients and 3 clinical sites, with 16
out of 17 contrast injections correctly detected and zero false detections. The proposed method is of general form and
can be extended for detection of contrast injection in other organs and/or applications.
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Cardiac magnetic resonance perfusion imaging (CMR) and computed tomography angiography (CTA) are widely used to
assess heart disease. CMR is used to measure the global and regional myocardial function and to evaluate the presence of
ischemia; CTA is used for diagnosing coronary artery disease, such as coronary stenoses. Nowadays, the hemodynamic
significance of coronary artery stenoses is determined subjectively by combining information on myocardial function with
assumptions on coronary artery territories. As the anatomy of coronary arteries varies greatly between individuals, we
developed a patient-specific tool for relating CTA and perfusion CMR data. The anatomical and functional information
extracted from CTA and CMR data are combined into a single frame of reference. Our graphical user interface provides
various options for visualization. In addition to the standard perfusion Bull's Eye Plot (BEP), it is possible to overlay a 2D
projection of the coronary tree on the BEP, to add a 3D coronary tree model and to add a 3D heart model. The perfusion
BEP, the 3D-models and the CTA data are also interactively linked. Using the CMR and CTA data of 14 patients, our
tool directly established a spatial correspondence between diseased coronary artery segments and myocardial regions with
abnormal perfusion. The location of coronary stenoses and perfusion abnormalities were visualized jointly in 3D, thereby
facilitating the study of the relationship between the anatomic causes of a blocked artery and the physiological effects on
the myocardial perfusion. This tool is expected to improve diagnosis and therapy planning of early-stage coronary artery
disease.
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Atrial fibrillation is a common cardiac arrhythmia in which aberrant electrical activity cause the atria to quiver
which results in irregular beating of the heart. Catheter ablation therapy is becoming increasingly popular in
treating atrial fibrillation, a procedure in which an electrophysiologist guides a catheter into the left atrium and
creates radiofrequency lesions to stop the arrhythmia. Typical visualization tools include bi-plane fluoroscopy,
2-D ultrasound, and electroanatomic maps, however, recently there has been increased interest in incorporating
preoperative surface models into the procedure. Typical strategies for registration include landmark-based and
surface-based methods. Drawbacks of these approaches include difficulty in accurately locating corresponding
landmark pairs and the time required to sample surface points with a catheter. In this paper, we describe a new
approach which models the catheter tip as a Gaussian kernel and eliminates the need to collect surface points by
instead using the stream of continuosly tracked catheter points. We demonstrate the feasibility of this technique
with a left atrial phantom model and compare the results with a standard surface based approach.
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During coronary artery angiography, a catheter is used to inject a contrast dye into the coronary arteries. Due
to the anatomical variation of the aorta and the coronary arteries in different humans, one common catheter
cannot be used for all patients. The cardiologists test different catheters for a patient and select the best catheter
according to the patient's anatomy. This procedure is time consuming and there is a slight chance of cancer from
excessive exposure to radiation. To overcome these problems, we propose a computer aided catheter selection
procedure. In this paper we present our approach for the angiography of the Right Coronary Artery (RCA).
Our approach involves segmentation of the aorta and coronary arteries, finding the centerline and computing the
Curve Angle (CA) and Curve Length (CL) between the aorta and the coronary arteries. We then compute CA
and CL of catheters and suggest a catheter with the closest CA and CL with respect to the aorta's and coronary
arteries' CA and CL. This solution avoids testing of many catheters during catheterization. The cardiologist
already gets the recommendation about the optimal catheter for the patient prior to the intervention.
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X-ray image guided angioplasty is a minimally invasive procedure that involves the insertion of a catheter into a
blood vessel to remove blockages to blood flow. There are several issues associated with conventional angioplasty
which cause risks for the patient (damage to blood vessels, dislodging plaques, etc.) and difficulties for the
clinician (X-ray exposure, fatigue, etc.). Autonomous or semi-autonomous robot-assisted catheter insertion is a
solution that can reduce these problems substantially. To perform autonomous catheter insertion, closed-loop
position control of the distal tip of the catheter is required during insertion. Therefore accurate real-time position
feedback is needed for this purpose. We have developed a real-time image processing algorithm for catheter tip
position tracking which has an acceptable performance but is sensitive to X-ray image artifacts caused by bones
and dense tissues. A magnetic tracking system (MTS) is another modality that has also been used for catheter
tip position tracking, but it is sensitive to external electromagnetic interferences and ferromagnetic material.
Combining the measurement data provided by both imaging and magnetic sensors can compensate for the
deficiencies of each and can also improve the robustness of catheter tip position tracking. We have developed a
Kalman filter based sensor fusion scheme to overcome deficiencies of both of these methods and create a reliable
real-time tracking of a catheter tip. Experiments have been performed by inserting a guide catheter into a model
of the vasculature. The method has been tested in presence of occlusion in the images and also electromagnetic
interference.
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Minimally invasive surgery is a medically complex discipline that can heavily benefit from computer assistance. One
way to assist the surgeon is to blend in useful information about the intervention into the surgical view using Augmented
Reality. This information can be obtained during preoperative planning and integrated into a patient-tailored model of
the intervention. Due to soft tissue deformation, intraoperative sensor data such as endoscopic images has to be acquired
and non-rigidly registered with the preoperative model to adapt it to local changes.
Here, we focus on a procedure that reconstructs the organ surface from stereo endoscopic images with millimeter
accuracy in real-time. It deals with stereo camera calibration, pixel-based correspondence analysis, 3D reconstruction
and point cloud meshing. Accuracy, robustness and speed are evaluated with images from a test setting as well as
intraoperative images. We also present a workflow where the reconstructed surface model is registered with a
preoperative model using an optical tracking system. As preliminary result, we show an initial overlay between an
intraoperative and a preoperative surface model that leads to a successful rigid registration between these two models.
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One of the main challenges related to computer-assisted laparoscopic surgery is the accurate registration of
pre-operative planning images with patient's anatomy. One popular approach for achieving this involves intraoperative
3D reconstruction of the target organ's surface with methods based on multiple view geometry. The
latter, however, require robust and fast algorithms for establishing correspondences between multiple images of
the same scene. Recently, the first endoscope based on Time-of-Flight (ToF) camera technique was introduced.
It generates dense range images with high update rates by continuously measuring the run-time of intensity
modulated light. While this approach yielded promising results in initial experiments, the endoscopic ToF
camera has not yet been evaluated in the context of related work. The aim of this paper was therefore to
compare its performance with different state-of-the-art surface reconstruction methods on identical objects. For
this purpose, surface data from a set of porcine organs as well as organ phantoms was acquired with four
different cameras: a novel Time-of-Flight (ToF) endoscope, a standard ToF camera, a stereoscope, and a High
Definition Television (HDTV) endoscope. The resulting reconstructed partial organ surfaces were then compared
to corresponding ground truth shapes extracted from computed tomography (CT) data using a set of local and
global distance metrics. The evaluation suggests that the ToF technique has high potential as means for intraoperative
endoscopic surface registration.
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The purpose of this paper is to present a detailed description of our real-time navigation system for computer assisted
surgery. The system was developed with laparoscopic partial nephrectomies as a first application scenario.
The main goal of the application is to enable tracking of the tumor position and orientation during a surgery.
Our system is based on ultrasound to CT registration and electromagnetic tracking. The basic idea is to process
tracking information to generate an augmented reality (AR) visualization of a tumor model in the camera image
of a laparoscopic camera. Thereby it enhances the surgeon's view on the current scene and therefore facilitates
higher safety during the surgery. So far we have applied our system in vitro during two phantom trials with a
surgeon which yielded promising results.
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The high recurrence rate of bladder cancer requires patients to undergo frequent surveillance screenings over their lifetime following initial diagnosis and resection. Our laboratory is developing panoramic stitching software that would compile several minutes of cystoscopic video into a single panoramic image, covering the entire bladder, for review by an urolgist at a later time or remote location. Global alignment of video frames is achieved by using a bundle adjuster that simultaneously recovers both the 3D structure of the bladder as well as the scope motion using only the video frames as input. The result of the algorithm is a complete 360° spherical panorama of the outer surface. The details of the software algorithms are presented here along with results from both a virtual cystoscopy as well from real endoscopic imaging of a bladder phantom. The software successfully stitched several hundred video frames into a single panoramic with subpixel accuracy and with no knowledge of the intrinsic camera properties, such as focal length and radial distortion. In the discussion, we outline future work in development of the software as well as identifying factors pertinent to clinical translation of this technology.
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This paper describes a navigation system for flexible endoscopes equipped with ultrasound scan
heads. For navigation and needle biopsy procedures it provides additional oblique slices from preoperative
computed tomography (CT) volumes which are displayed with the corresponding endoscopic
ultrasound (US) image. In contrast to similar systems an additional abdominal 3D ultrasound image
is used to achieve the required registration. Two different approaches are compared: one method
is based on direct inter-modal registration between abdominal 3D ultrasound and CT volume. The
second method uses another 3D US scan taken preoperatively before the CT scan. Here, the CT is
calibrated by means of an optical tracking system and the transformation between CT and the calibrated
3D US can be calculated without image registration. Before intervention, a pre-interventional
3D US is registered intra-modal to the preoperative US. This second method invoked to be the more
robust and accurate procedure. For experimental studies a phantom has been developed which consists
of a plastic tube inside a water tank. For error evaluation small plastic spheres have been fixed
around the tube at different distances. First results give an overall error of 3.9 mm for the first
method while the overall error for the intramodal method amounted to 3.1 mm.
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Virtual colonoscopy provides techniques not available in optical colonoscopy, an exciting one being the ability to
perform an electronic biopsy. An electronic biopsy image is created using ray-casting volume rendering of the CT data
with a translucent transfer function mapping higher densities to red and lower densities to blue. The resulting image
allows the physician to gain insight into the internal structure of polyps. Benign tissue and adenomas can be
differentiated; the former will appear as homogeneously blue and the latter as irregular red structures. Although this
technique is now common, is included with clinical systems, and has been used successfully for computer aided
detection, there has so far been no study to evaluate the effectiveness of a physician using electronic biopsy in
determining the pathological state of a polyp. We present here such a study, wherein an experienced radiologist ranked
polyps based on electronic biopsy alone per scan (supine and prone), as well as both combined. Our results show a
correct identification 77% of the time using prone or supine images alone, and 80% accuracy using both. Using ROC
analysis based on this study with one reader and a modest sample size, the combined score is not significantly higher
than using a single electronic biopsy image alone. However, our analysis indicates a trend of superiority for the
combined ranking that deserves a follow-up confirmatory study with a larger sample and more readers. This study
yields hope that an improved electronic biopsy technique could become a primary clinical diagnosis method.
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For trauma and orthopedic surgery, maneuvering a mobile C-arm X-ray device into a desired position in order
to acquire the right picture is a routine task. The precision and ease of use of the C-arm positioning becomes
even more important for more advanced imaging techniques as parallax-free X-ray image stitching, for example.
Standard mobile C-arms have only five degrees of freedom (DOF), which definitely restricts their motions that
have six DOF in 3D Cartesian space. We have proposed a method to model the kinematics of the mobile Carm
and operating table as an integrated 6DOF C-arm X-ray imaging system.1 This enables mobile C-arms
to be positioned relative to the patient's table with six DOF in 3D Cartesian space. Moving mobile C-arms
to a desired position and orientation requires finding the necessary joint values, which is an inverse kinematics
problem. In this paper, we present closed-form solutions, i.e. analytic expressions, obtained in an algebraic way
for the inverse kinematics problem of the 6DOF C-arm model. In addition, we implement a 6DOF C-arm system
for interactively radiation-free C-arm positioning based on a continuous guidance from C-arm pose estimation.
For this we employ a visual marker pattern attached under the operating table and a mobile C-arm system
augmented by a video camera and mirror construction. In our experiment, repositioning C-arm to a pre-defined
pose in a phantom study demonstrates the practicality and accuracy of our developed 6DOF C-arm system.
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We present a spectral-based method for the 2D/3D rigid registration of X-ray images to a CT scan. The method
uses a Fourier-based representation to decompose the six rigid transformation parameters problem into a twoparameter
out-of-plane rotation and a four-parameter in-plane transformation problems. Preoperatively, a set
of Digitally Reconstructed Radiographs (DRRs) are generated offline from the CT in the expected in-plane
location ranges of the fluoroscopic X-ray imaging devices. Each DRR is transformed into a imaging device
in-plane invariant features space. Intraoperatively, a few 2D projections of the patient anatomy are acquired
with an X-ray imaging device. Each projection is transformed into its in-plane invariant representation. The
out-of-plane parameters are first computed by maximization of the Normalized Cross-Correlation between the
invariant representations of the DRRs and the X-ray images. Then, the in-plane parameters are computed with
the phase correlation method based on the Fourier-Mellin transform. Experimental results on publicly available
data sets show that our method can robustly estimate the out-of-plane parameters with accuracy of 1.5° in less
than 1sec for out-of-plane rotations of 10° or more, and perform the entire registration in less than 10secs.
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Eduard H. J. Voormolen, Marijn van Stralen, Peter A. Woerdeman, Josien P. W. Pluim, Herke Jan Noordmans, Luca Regli, Jan Willem Berkelbach van der Sprenkel, Max A. Viergever
Proceedings Volume Medical Imaging 2011: Visualization, Image-Guided Procedures, and Modeling, 79641C (2011) https://doi.org/10.1117/12.878594
Approaches through the temporal bone require surgeons to drill away bone to expose a target skull base lesion while
evading vital structures contained within it, such as the sigmoid sinus, jugular bulb, and facial nerve. We hypothesize
that an augmented neuronavigation system that continuously calculates the distance to these structures and warns if the
surgeon drills too close, will aid in making safe surgical approaches. Contemporary image guidance systems are lacking
an automated method to segment the inhomogeneous and complexly curved facial nerve. Therefore, we developed a
segmentation method to delineate the intra-temporal facial nerve centerline from clinically available temporal bone CT
images semi-automatically. Our method requires the user to provide the start- and end-point of the facial nerve in a
patient's CT scan, after which it iteratively matches an active appearance model based on the shape and texture of forty
facial nerves. Its performance was evaluated on 20 patients by comparison to our gold standard: manually segmented
facial nerve centerlines. Our segmentation method delineates facial nerve centerlines with a maximum error along its
whole trajectory of 0.40±0.20 mm (mean±standard deviation). These results demonstrate that our model-based
segmentation method can robustly segment facial nerve centerlines. Next, we can investigate whether integration of this
automated facial nerve delineation with a distance calculating neuronavigation interface results in a system that can
adequately warn surgeons during temporal bone drilling, and effectively diminishes risks of iatrogenic facial nerve palsy.
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Percutaneous femoroplasty [1], or femoral bone augmentation, is a prospective alternative treatment for
reducing the risk of fracture in patients with severe osteoporosis. We are developing a surgical robotics system that will
assist orthopaedic surgeons in planning and performing a patient-specific, augmentation of the femur with bone cement.
This collaborative project, sponsored by the National Institutes of Health (NIH), has been the topic of previous
publications [2],[3] from our group. This paper presents modifications to the pose recovery of a fluoroscope tracking
(FTRAC) fiducial during our process of 2D/3D registration of X-ray intraoperative images to preoperative CT data. We
show improved automata of the initial pose estimation as well as lower projection errors with the advent of a multiimage
pose optimization step.
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Cochlear implantation is a surgical procedure for treating patients with hearing loss in which an electrode array is
inserted into the cochlea. The traditional surgical approach requires drilling away a large portion of the bone behind the
ear to provide anatomical reference and access to the cochlea. A minimally-invasive technique, called percutaneous
cochlear implantation (PCI), has been proposed that involves drilling a linear path from the lateral skull to the cochlea
avoiding vital structures and inserting the implant using that drilled path. The steps required to achieve PCI safely
include: placing three bone-implanted markers surrounding the ear, obtaining a CT scan, planning a surgical path to the
cochlea avoiding vital anatomy, designing and constructing a microstereotactic frame that mounts on the markers and
constrains the drill to the planned path, affixing the frame on the markers, using it to drill to the cochlea, and inserting
the electrode through the drilled path. We present in this paper a cadaveric study demonstrating the PCI technique on
three temporal bone cadaveric specimens for inserting electrode array into the cochlea. A custom fixture, called a
Microtable, which is a type of microstereotactic frame that can be constructed in less than five minutes, was fabricated
for each specimen and used to reach the cochlea. The insertion was successfully performed on all three specimens. Postinsertion
CT scans confirm the correct placement of the electrodes inside the cochlea without any damage to the facial
nerve.
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In ultrasound-guided needle insertion procedures, tracking of the needle relative to the ultrasound image is beneficial for
needle trajectory planning and guidance. A single camera closed-form method is proposed for automatic real-time
trajectory tracking with a low-cost camera mounted directly on the ultrasound transducer. The camera is calibrated to the
ultrasound image coordinates. By mounting the camera on the transducer, issues of visual obstruction are reduced and
accuracy of tracking is increased compared to camera-tracking systems with a fixed case. Compared to previous work
with stereo cameras, a single camera further reduces cost, complexity and size, but requires a needle with known
markings. The proposed solution uses the depth markings etched on many common needles (e.g. epidural needle). A
fully automatic image processing method has been developed for real-time identification of the needle trajectory using a
novel closed-form solution based on three identified markings and the camera's intrinsic calibration parameters. The
trajectory of the needle relative to the ultrasound image is calculated and displayed. Validation compares the calculated
intersection of the needle trajectory to the ultrasound image with the depiction of the actual needle intersection in the
image. The overall error is 3.0 ± 2.6 mm for a low-cost 640×480 pixel USB camera.
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A feature-based registration was developed to align biplane and tracked ultrasound images of the aortic root with
a preoperative CT volume. In transcatheter aortic valve replacement, a prosthetic valve is inserted into the aortic
annulus via a catheter. Poor anatomical visualization of the aortic root region can result in incorrect positioning,
leading to significant morbidity and mortality. Registration of pre-operative CT to transesophageal ultrasound
and fluoroscopy images is a major step towards providing augmented image guidance for this procedure. The
proposed registration approach uses an iterative closest point algorithm to register a surface mesh generated from
CT to 3D US points reconstructed from a single biplane US acquisition, or multiple tracked US images. The use
of a single simultaneous acquisition biplane image eliminates reconstruction error introduced by cardiac gating
and TEE probe tracking, creating potential for real-time intra-operative registration. A simple initialization
procedure is used to minimize changes to operating room workflow. The algorithm is tested on images acquired
from excised porcine hearts. Results demonstrate a clinically acceptable accuracy of 2.6mm and 5mm for tracked
US to CT and biplane US to CT registration respectively.
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PURPOSE: Thermal ablation is a popular method in local cancer management; however it is extremely challenging
to predict thermal changes in vivo. Ultrasound could be a convenient and inexpensive imaging modality
for real-time monitoring of the ablation, but the required advanced image processing algorithms need extensive
validation. Our goal is to design and develop a reliable test-bed for validation of these monitoring algorithms.
METHOD: We previously developed a test-bed, consisting of ablated tissue sample and fiducial lines embedded
in tissue-mimicking gel.1 The gel block is imaged by ultrasound and sliced to acquire pathology images. Following
fiducial localization in both image modalities, the pathology and US data were registered. Ground truth
ablated region is retrieved from pathology images and compared to the result of the ultrasound-based processing
in 3D space. We improved on this platform to resolve limitations that hindered its usage in a larger-scale validation
study. A simulator for evaluating and optimizing different line fiducial structures was implemented, and
a new fiducial line structure was proposed. RESULTS: The new proposed fiducial configuration outperforms
the previous in terms of accuracy, fiducial visibility, and use of larger tissue samples. Simulation results show
improvement in pose recovery accuracy using our proposed fiducial structure, reducing target registration error
(TRE) by 34%. Inaccurate pixel spacing information and fiducial localization noise are the main sources of error
in slice pose recovery. CONCLUSION: A new generation of test-bed was developed, with software that does
not require lengthy manual data processing, and is easier to maintain and extend. Further experimental work is
required to optimize phantom preparation and precise pixel spacing computation.
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Needle tip dexterity is advantageous for transthoracic lung biopsies, which are typically performed with rigid,
straight biopsy needles. By providing intraoperative compensation for trajectory error and lesion motion, tendon-driven
biopsy needles may reach smaller or deeper nodules in fewer attempts, thereby reducing trauma. An
image-guided robotic system that uses these needles also has the potential to reduce radiation exposure to the
patient and physician. In this paper, we discuss the design, workflow, kinematic modeling, and control of both
the needle and a compact and inexpensive robotic prototype that can actuate the tendon-driven needle for
transthoracic lung biopsy. The system is designed to insert and steer the needle under Computed Tomography
(CT) guidance. In a free-space targeting experiment using a discrete proportional control law with digital camera
feedback, we show a position error of less than 1 mm achieved using an average of 8.3 images (n=3).
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Liver tumor, one of the most wide-spread diseases, has a very high mortality in China. To improve success rates of liver
surgeries and life qualities of such patients, we implement an interactive liver surgery planning system based on contrastenhanced
liver CT images. The system consists of five modules: pre-processing, segmentation, modeling, quantitative
analysis and surgery simulation. The Graph Cuts method is utilized to automatically segment the liver based on an
anatomical prior knowledge that liver is the biggest organ and has almost homogeneous gray value. The system supports
users to build patient-specific liver segment and sub-segment models using interactive portal vein branch labeling, and to
perform anatomical resection simulation. It also provides several tools to simulate atypical resection, including resection
plane, sphere and curved surface. To match actual surgery resections well and simulate the process flexibly, we extend
our work to develop a virtual scalpel model and simulate the scalpel movement in the hepatic tissue using multi-plane
continuous resection. In addition, the quantitative analysis module makes it possible to assess the risk of a liver surgery.
The preliminary results show that the system has the potential to offer an accurate 3D delineation of the liver anatomy, as
well as the tumors' location in relation to vessels, and to facilitate liver resection surgeries. Furthermore, we are testing
the system in a full-scale clinical trial.
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Bronchoscopes contain wide-angle lenses that produce a large field of view but suffer from radial distortion. For
image-guided bronchoscopy, geometric calibration including distortion correction is essential for comparing video
images to renderings developed from 3D computed-tomography (CT) images. This paper describes an easy-to-use
system for bronchoscopic video-distortion correction and studies the robustness of the resulting calibration over a
wide range of conditions. The internal calibration method integrated into the system incorporates a well-known
camera calibration framework devised for general camera-distortion correction. The robustness study considers
the calibration results as follows: (1) varying lighting during video capture, (2) using different number of captured
images for parameter estimation, (3) changing camera pose with respect to the calibration pattern, (4) recording
temporal changes in estimated parameters, and (5) comparing parameters between different bronchoscopes of a
same model. Multiple bronchoscopes were successfully calibrated under a variety of conditions.
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Computer assisted navigation systems that combine real-time endoscopy images with pre-operative volumetric data sets
aim at improving the physician's understanding of the underlying anatomical structures. To achieve accurate and safe
guidance these systems are required to provide a consistent representation of the physical world. This implies that all
data streams are synchronized. In our case, we are dealing with synchronization of tracking data and a video stream
obtained by a tracked endoscope. Previously, such synchronization was obtained pre-operatively using phantoms. This
type of approach assumes a constant latency between the data streams and is less desirable for clinical use due to the
required additional hardware. In this work we describe an online temporal synchronization method. The method is based
on the observation that in clinical practice the endoscope is not in constant motion. By identifying corresponding
stationary points in the video and tracking streams temporal synchronization can be performed online in a manner that is
transparent to the user. Initial evaluation of our approach in a laboratory study has shown that it provides comparable
estimates to a phantom based approach we had previously proposed.
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Registration is a key technology in image-guided navigation systems. By aligning pre-operative images with the
intra-operative setting these systems provide visual feedback that improves the physician's understanding of the
spatial relationships between anatomical structures and surgical tools. Most often the alignment is obtained
using fiducials. Another option is to replace the use of fiducials with intra-operative imaging. Two dimensional
ultrasound (US) is a widely available intra-operative non-ionizing imaging modality. To utilize this modality for
registration one must first perform spatial calibration of the US. In this work we describe the implementation
of three spatial calibration methods as part of the image-guided surgery toolkit (IGSTK). The implementation
follows the IGSTK calibration framework, separating algorithmic aspects from user interaction aspects of the
calibration. Our calibration framework includes three methods. The first is a phantom-less method using a
tracked pointer tool in addition to the tracked US, the second method uses a cross-wire phantom, and the third
method is based on the use of a plane phantom.
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The treatment of atrial fibrillation has gained increasing importance in the field of
computer-aided interventions. State-of-the-art treatment involves the electrical isolation of the
pulmonary veins attached to the left atrium under fluoroscopic X-ray image guidance. Due to
the rather low soft-tissue contrast of X-ray fluoroscopy, the heart is difficult to see. To overcome
this problem, overlay images from pre-operative 3-D volumetric data can be used to add
anatomical detail. Unfortunately, these overlay images are static at the moment, i.e., they do not
move with respiratory and cardiac motion. The lack of motion compensation may impair X-ray
based catheter navigation, because the physician could potentially position catheters incorrectly.
To improve overlay-based catheter navigation, we present a novel two stage approach for respiratory
and cardiac motion compensation. First, a cascade of boosted classifiers is employed to
segment a commonly used circumferential mapping catheter which is firmly fixed at the ostium
of the pulmonary vein during ablation. Then, a 2-D/2-D model-based registration is applied to
track the segmented mapping catheter. Our novel hybrid approach was evaluated on 10 clinical
data sets consisting of 498 fluoroscopic monoplane frames. We obtained an average 2-D tracking
error of 0.61 mm, with a minimum error of 0.26 mm and a maximum error of 1.62 mm.
These results demonstrate that motion compensation using registration-based catheter tracking
is both feasible and accurate. Using this approach, we can only estimate in-plane motion. Fortunately,
compensating for this is often sufficient for EP procedures where the motion is governed
by breathing.
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Atrial fibrillation is the most common heart arrhythmia and a leading cause of stroke.
The treatment option of choice is radio-frequency catheter ablation, which is performed in electrophysiology
labs using C-Arm X-ray systems for navigation and guidance. The goal is to
electrically isolate the pulmonary vein-left atrial junction thereby rendering myocardial fibers
responsible for induction and maintenance of AF inactive. The use of overlay images for fluoroscopic
guidance may improve the quality of the ablation procedure, and can reduce procedure
time. Overlay images, acquired using CT, MRI, or C-arm CT, can add soft-tissue information,
otherwise not visible under X-ray. MRI can be used to image a wide variety of anatomical
details without ionizing radiation. In this paper, we present a method to register a 3-D MRI
volume to 2-D biplane X-ray images using the coronary sinus. Current approaches require registration
of the overlay images to the fluoroscopic images to be performed after the trans-septal
puncture, when contast agent can be administered. We present a new approach for registration
to align overlay images before the trans-septal puncture. To this end, we manually extract the
coronary sinus from pre-operative MRI and register it to a multi-electorde catheter placed in the
coronary sinus.
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Diagnosis and treatment of coronary heart disease are performed in the catheter laboratory using an angiographic X-ray
C-arm system. The morphology of the coronary tree and potentially ischemic lesions are determined in 2D projection
views. The hemodynamic impact of the lesion would be valuable information for treatment decision. Using other
modalities for functional imaging is disrupting the clinical workflow since the patient has to be transferred from the
catheter laboratory to another scanner, and back to the catheter laboratory for performing the treatment. In this work a
novel technology is used for simultaneous 3D imaging of first pass perfusion and the morphology of the coronary tree
from a single rotational angiogram. A selective, single shot of contrast agent of less than 20ml directly into the
coronaries is sufficient for a proper contrast resolution. Due to the long acquisition time cardiac motion has to be
considered. A novel reconstruction technique for estimation and compensation of cardiac motion from the acquired
projection data is used. The overlay of the 3D structure of the coronary tree and the perfusion image shows the
correlation of myocardial areas and the associated coronary sections supporting that region. In a case example scar
lesions caused by a former myocardial infarct are investigated. A first pass perfusion defect is found which is validated
by a late enhancement magnetic resonance image. No ischemic defects are found. The non vital regions are still
supported by the coronary vasculature.
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The segmentation of anatomical structures in Computed Tomography Angiography (CTA) is a pre-operative task useful in image guided surgery. Even though very robust and precise methods have been developed to help achieving a reliable segmentation (level sets, active contours, etc), it remains very time consuming both in terms of manual interactions and in terms of computation time.
The goal of this study is to present a fast method to find coarse anatomical structures in CTA with few parameters, based on hierarchical clustering. The algorithm is organized as follows: first, a fast non-parametric histogram clustering method is proposed to compute a piecewise constant mask. A second step then indexes all the space-connected regions in the piecewise constant mask. Finally, a hierarchical clustering is achieved to build a graph representing the connections between the various regions in the piecewise constant mask.
This step builds up a structural knowledge about the image. Several interactive features for segmentation are presented, for instance association or disassociation of anatomical structures. A comparison with the Mean-Shift algorithm is presented.
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Time-resolved 3-D imaging of the heart is a major research topic in the medical imaging community. Recent advances in the interventional cardiac 3-D imaging from rotational angiography (C-arm CT) are now also making 4-D imaging feasible during procedures in the catheter laboratory. State-of-the-art reconstruction algorithms try to estimate the cardiac motion and utilize the motion field to enhance the reconstruction of a stable cardiac phase (diastole). The available data offers a handful of opportunities during interventional procedures, e.g. the ECG-synchronized dynamic roadmapping or the computation and analysis of functional parameters. In this paper we will demonstrate that the motion vector field (MVF) that is output by motion compensated image reconstruction algorithms is in general not directly usable for animation and motion analysis. Dependent on the algorithm different defects are investigated. A primary issue is that the MVF needs to be inverted, i.e. the wrong direction of motion is provided. A second major issue is the non-periodicity of cardiac motion. In algorithms which compute a non-periodic motion field from a single rotation the in depth motion information along viewing direction is missing, since this cannot be measured in the projections. As a result, while the MVF improves reconstruction quality, it is insufficient for motion animation and analysis. We propose an algorithm to solve both problems, i.e. inversion and missing in-depth information in a unified framework. A periodic version of the MVF is approximated. The task is formulated as a linear optimization problem where a parametric smooth motion model based on B-splines is estimated from the MVF. It is shown that the problem can be solved using a sparse QR factorization within a clinical feasible time of less than one minute. In a phantom experiment using the publicly available CAVAREV platform, the average quality of a non-periodic animation could be increased by 39% by applying the proposed periodization and inversion method.
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Image-guided bronchoscopy usually requires to track the bronchoscope camera position and orientation to align
the preinterventional 3-D computed tomography (CT) images to the intrainterventional 2-D bronchoscopic video
frames. Current state-of-the-art image-based algorithms often fail in bronchoscope tracking due to shortages
of information on depth and rotation around the viewing (running) direction of the bronchoscope camera. To
address these problems, this paper presents a novel bronchoscope tracking method for bronchoscopic navigation
based on a low-cost optical mouse sensor, bronchial structure information, and image registration. We first utilize
an optical mouse senor to automatically measure the insertion depth and the rotation of the viewing direction
along the bronchoscope. We integrate the outputs of such a 2-D sensor by performing a centerline matching
on the basis of bronchial structure information before optimizing the bronchoscope camera motion parameters
during image registration. An assessment of our new method is implemented on phantom data. Experimental
results illustrate that our proposed method is a promising means for bronchoscope tracking, compared to our
previous image-based method, significantly improving the tracking performance.
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Image-based camera motion estimation from video or still images is a difficult problem in the field of computer vision.
Many algorithms have been proposed for estimating intrinsic camera parameters, detecting and matching features
between images, calculating extrinsic camera parameters based on those features, and optimizing the recovered
parameters with nonlinear methods. These steps in the camera motion inference process all face challenges in practical
applications: locating distinctive features can be difficult in many types of scenes given the limited capabilities of current
feature detectors, camera motion inference can easily fail in the presence of noise and outliers in the matched features,
and the error surfaces in optimization typically contain many suboptimal local minima. The problems faced by these
techniques are compounded when they are applied to medical video captured by an endoscope, which presents further
challenges such as non-rigid scenery and severe barrel distortion of the images. In this paper, we study these problems
and propose the use of prior probabilities to stabilize camera motion estimation for the application of computing
endoscope motion sequences in colonoscopy.
Colonoscopy presents a special case for camera motion estimation in which it is possible to characterize typical motion
sequences of the endoscope. As the endoscope is restricted to move within a roughly tube-shaped structure,
forward/backward motion is expected, with only small amounts of rotation and horizontal movement. We formulate a
probabilistic model of endoscope motion by maneuvering an endoscope and attached magnetic tracker through a
synthetic colon model and fitting a distribution to the observed motion of the magnetic tracker. This model enables us to
estimate the probability of the current endoscope motion given previously observed motion in the sequence. We add
these prior probabilities into the camera motion calculation as an additional penalty term in RANSAC to help reject
improbable motion parameters caused by outliers and other problems with medical data. This paper presents the
theoretical basis of our method along with preliminary results on indoor scenes and synthetic colon images.
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Suboptimal results of angioplasty procedures have been correlated to arterial damage during balloon inflation. We
propose to monitor balloon inflation during the angioplasty procedure by detecting the balloon contours with
intravascular optical coherence tomography (IVOCT). This will shed more light on the interaction between the balloon
and the artery and to assess the artery's mechanical response. An automatic edge detection algorithm is applied for
detection of the outer surface of an inflating balloon in a porcine artery in a beating heart experiment. A compliant
balloon is inflated to deform the artery. IVOCT monitoring of balloon inflation is performed at a rate of 30 frames per
second. During inflation, the balloon engages the arterial wall. Therefore, the characterization of the diameter of the
inflated balloon leads to a characterization of the luminal diameter of the vessel. This provides precise information about
the artery response to a simulated angioplasty procedure, information currently not provided by any other existing
technique. In the current experiment, balloon inflation characterization is based on 356 IVOCT frames during which the
estimated balloon diameter increases approximately from 1.8 mm to 2.9 mm.
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Brain perfusion CT using a C-arm angiography system capable of CT-like imaging could optimize patient treatment
during stroke therapy procedures. For this application, an intra-arterial contrast bolus injection at the
aortic arch could be used provided that the location of the injection catheter enables uniform distribution of the
bolus into the two common carotid arteries (CCA). In this work, we present a novel method to support optimal
injection catheter placement by providing additional quantitative information about the distribution of the contrast
bolus into the CCAs. Our fully automatic method uses 2-D digital subtraction angiography (DSA) images
following a test bolus injection. It segments both CCAs and computes the relative contrast distribution. We
have tested the method in DSA data sets from 5 healthy pigs and our method achieved successful segmentation
of both CCAs in all data sets. The results showed that the contrast is uniformly distributed (mean relative
difference less or equal than 10%) if the injection location is properly chosen.
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This study assesses the accuracy of a new transesophageal (TEE) ultrasound (US) fluoroscopy registration
technique designed to guide percutaneous aortic valve replacement. In this minimally invasive procedure, a
valve is inserted into the aortic annulus via a catheter. Navigation and positioning of the valve is guided
primarily by intra-operative fluoroscopy. Poor anatomical visualization of the aortic root region can result in
incorrect positioning, leading to heart valve embolization, obstruction of the coronary ostia and acute kidney
injury. The use of TEE US images to augment intra-operative fluoroscopy provides significant improvements to
image-guidance.
Registration is achieved using an image-based TEE probe tracking technique and US calibration. TEE probe
tracking is accomplished using a single-perspective pose estimation algorithm. Pose estimation from a single
image allows registration to be achieved using only images collected in standard OR workflow. Accuracy of this
registration technique is assessed using three models: a point target phantom, a cadaveric porcine heart with
implanted fiducials, and in-vivo porcine images. Results demonstrate that registration can be achieved with
an RMS error of less than 1.5mm, which is within the clinical accuracy requirements of 5mm. US-fluoroscopy
registration based on single-perspective pose estimation demonstrates promise as a method for providing guidance
to percutaneous aortic valve replacement procedures. Future work will focus on real-time implementation and a
visualization system that can be used in the operating room.
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We have developed a 5.5mm and 10mm dual optical channel laparoscope that combines both exit channels into a
single, standard, endoscopic eye cup which attaches directly to a single, conventional HD camera head. We have also
developed image processing software that auto-calibrates, aligns, enhances and processes the image so that it can be
displayed on a stereo/3D display to achieve a true 3D effect.
The advantages to the end user for such a 3D system are that they do not have to purchase a new camera system, all of
their existing scopes are still available to use, as are all integrated OR features. They will be able to add 3D capability to
current HD system by purchasing only stereo scopes and a small video processing computer box and adding a 2D/3D
HD capable monitor.
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We present a method towards optimization of multiple ablation probe placement to provide efficient coverage
of a tumor for thermal therapy while respecting clinical needs such as limiting the sites of probe insertions at
the pleura/liver surface, choosing secure probe trajectories and locations, avoiding ablation of critical structures,
reducing ablation of healthy tissue and overlap of ablation zones. The ablation optimizer treats each ablation
location independently, and the number of ablation probe placements itself is treated as a variable to be optimized.
This allows us to potentially feedback the ablation after deployment and re-optimize the next steps during the
plan. The optimization method uses a new class of derivate-free algorithms for solving a non-linear mixed
variable problem with hard and soft constraints derived from clinical images. Our methods use discretization
of the ablation volume, which can accommodate irregular shape of the ablation zone. The non-gradient based
strategy produce new candidates to yield a feasible solution within a few iterations. In our simulation experiments
this strategy typically reduced the ablation zone overlap and ablated healthy tissue ablated by 46% and 29%,
respectively in a single iteration, resulting in a feasible solution to be found within 35 iterations. Our method
for optimization provides efficient implementation for planning the coverage of a tumor while respecting clinical
constraints. The ablation planning can be combined with navigation assistance to enable accurate translation
and feedback of the plan.
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PURPOSE: Development of ultrasound-based tumor ablation monitoring systems requires extensive validation.
Validation is based on the comparison of ablated regions, computed from ultrasound images, to the ground truth region
observed on histopathology images. Registration of ultrasound and histopathology images can be efficiently
implemented by localizing fiducial lines embedded in the test phantom. Manual fiducial localization is time consuming
and may be inaccurate. Current automatic localization algorithms were designed for use on images containing easily
detectable fiducials in clear water, while the images produced by the ablation monitoring platform contain fiducials and
ablated tissue embedded in tissue-mimicking gel. Our goal was to develop an automatic fiducial localization algorithm
for the ablation monitoring platform. METHOD: A previously existing algorithm for detecting fishing line in water for
ultrasound probe calibration, created by Chen et al., was tested on ultrasound images of an ablation phantom. Fiducial
and line point detection parameters were determined by running the algorithm multiple times with different parameter
sets and searching for the set that results in the best detection success rate. The fiducial intensity scoring method was
modified to use intensities from an unaltered image; this greatly reduced the number of incorrectly identified fiducials.
Line finding was modified to suit the ablation phantom geometry. RESULTS: The new algorithm was tested by
comparing the automatic localization results to manually identified fiducial positions. Using the optimized parameters, it
was found to have a 94.1 % success rate on the tested images. Fiducial localization error was defined as the difference
between the manually segmented positions and the positions found by the algorithm. Fiducial localization error was -
0.04±0.18mm along the x-axis, and -0.09±0.14mm along the y-axis. CONCLUSION: We have developed an automatic
algorithm that detects line fiducials at a high success rate in complex phantoms containing a tissue sample embedded in
tissue-mimicking gel.
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Intraoperative imaging modalities are becoming more prevalent in recent years, and the need for integration of these modalities
with surgical guidance is rising, creating new possibilities as well as challenges. In the context of such emerging
technologies and new clinical applications, a software architecture for cone-beam CT (CBCT) guided surgery has been
developed with emphasis on binding open-source surgical navigation libraries and integrating intraoperative CBCT with
novel, application-specific registration and guidance technologies. The architecture design is focused on accelerating
translation of task-specific technical development in a wide range of applications, including orthopaedic, head-and-neck,
and thoracic surgeries. The surgical guidance system is interfaced with a prototype mobile C-arm for high-quality CBCT
and through a modular software architecture, integration of different tools and devices consistent with surgical workflow
in each of these applications is realized. Specific modules are developed according to the surgical task, such as: 3D-3D
rigid or deformable registration of preoperative images, surgical planning data, and up-to-date CBCT images; 3D-2D
registration of planning and image data in real-time fluoroscopy and/or digitally reconstructed radiographs (DRRs);
compatibility with infrared, electromagnetic, and video-based trackers used individually or in hybrid arrangements;
augmented overlay of image and planning data in endoscopic or in-room video; real-time "virtual fluoroscopy" computed
from GPU-accelerated DRRs; and multi-modality image display. The platform aims to minimize offline data processing
by exposing quantitative tools that analyze and communicate factors of geometric precision. The system was
translated to preclinical phantom and cadaver studies for assessment of fiducial (FRE) and target registration error (TRE)
showing sub-mm accuracy in targeting and video overlay within intraoperative CBCT. The work culminates in the development
of a CBCT guidance system (reported here for the first time) that leverages the technical developments in Carm
CBCT and associated technologies for realizing a high-performance system for translation to clinical studies.
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Image-guided therapy systems generally require registration of pre-operative planning data with the patient's anatomy. One common approach to achieve this is to acquire intra-operative surface data and match it to surfaces extracted from the planning image. Although increasingly popular for surface generation in general, the novel Time-of-Flight (ToF) technology has not yet been applied in this context. This may be attributed to the fact that the ToF range images are subject to considerable noise. The contribution of this study is two-fold. Firstly, we present an adaption of the well-known bilateral filter for denoising ToF range images based on the noise characteristics of the camera. Secondly, we assess the quality of organ surfaces generated from ToF range data with and without bilateral smoothing using corresponding high resolution CT data as ground truth. According to an evaluation on five porcine organs, the root mean squared (RMS) distance between the denoised ToF data points and the reference computed tomography (CT) surfaces ranged from 3.0 mm (lung) to 9.0 mm (kidney). This corresponds to an error-reduction of up to 36% compared to the error of the original ToF surfaces.
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Laser range scanning an organ surface intraoperatively provides a cost effective and accurate means of measuring
geometric changes in tissue. A novel laser range scanner with integrated tracking was designed, developed, and analyzed
with the goal of providing intraoperative surface data during neurosurgery. The scanner is fitted with passive spheres to
be optically tracked in the operating room. The design notably includes a single-lens system capable of acquiring the
geometric information (as a Cartesian point cloud) via laser illumination and charge-coupled device (CCD) collection, as
well as the color information via visible light collection on the same CCD. The geometric accuracy was assessed by
scanning a machined phantom of known dimensions and comparing relative distances of landmarks from the point cloud
to the known distances. The ability of the scanner to be tracked was first evaluated by perturbing its orientation in front
of the optical tracking camera and recording the number of spheres visible to the camera at each orientation, and then by
observing the variance in point cloud locations of a fixed object when the tracking camera is moved around the scanner.
The scanning accuracy test resulted in an RMS error of 0.47 mm with standard deviation of 0.40 mm. The sphere
visibility test showed that four diodes were visible in most of the probable operating orientations, and the overall
tracking standard deviation was observed to be 1.49 mm. Intraoperative collection of cortical surface scans using the new
scanner is currently underway.
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A prototype mobile C-arm for cone-beam CT (CBCT) has been translated to a prospective clinical trial in head and neck
surgery. The flat-panel CBCT C-arm was developed in collaboration with Siemens Healthcare, and demonstrates both
sub-mm spatial resolution and soft-tissue visibility at low radiation dose (e.g., <1/5th of a typical diagnostic head CT).
CBCT images are available ~15 seconds after scan completion (~1 min acquisition) and reviewed at bedside using
custom 3D visualization software based on the open-source Image-Guided Surgery Toolkit (IGSTK). The CBCT C-arm
has been successfully deployed in 15 head and neck cases and streamlined into the surgical environment using human
factors engineering methods and expert feedback from surgeons, nurses, and anesthetists. Intraoperative imaging is
implemented in a manner that maintains operating field sterility, reduces image artifacts (e.g., carbon fiber OR table) and
minimizes radiation exposure. Image reviews conducted with surgical staff indicate bony detail and soft-tissue
visualization sufficient for intraoperative guidance, with additional artifact management (e.g., metal, scatter) promising
further improvements. Clinical trial deployment suggests a role for intraoperative CBCT in guiding complex head and
neck surgical tasks, including planning mandible and maxilla resection margins, guiding subcranial and endonasal
approaches to skull base tumours, and verifying maxillofacial reconstruction alignment. Ongoing translational research
into complimentary image-guidance subsystems include novel methods for real-time tool tracking, fusion of endoscopic
video and CBCT, and deformable registration of preoperative volumes and planning contours with intraoperative CBCT.
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Poster Session: Localization and Tracking Technologies
Although dysesthesia is a common and persistent surgical complication, there is no
accepted method for quantitatively tracking affected skin. To address this, two types
of computer vision technologies were tested in a total of four configurations. Surface
regions on plastic models of limbs were delineated with colored tape, imaged, and
compared with computed tomography scans. The most accurate system used visually
projected texture captured by a binocular stereo camera, capable of measuring areas
to within 0.05% of the ground-truth areas with 1.4% variance. This simple, inexpensive
technology shows promise for postoperative monitoring of dysesthesia surrounding
surgical scars.
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This paper introduces a novel alignment and calibration method for high frequency ultrasound (HFUS) and optical
coherence tomography (OCT) 1D transducers. 2D images are constructed by means of translation of the transducers
using a linear motor stage. Physical alignment of the transducers is needed in order to capture images of the same crosssectional
plane, and calibration is needed to determine the relative coordinates of the images, including the image skew.
A dual wedge-tri step phantom is created for both alignment and calibration. This phantom includes two symmetrical
wedges and three steps that provide the user with visual feedback on how well the scan plane is aligned with the midplane
of the phantom. The phantom image consists of five line segments, each of which corresponds to one of the
wedges or steps. The slopes and positions of the lines are extracted from the image and compared with the phantom
model. The scan plane parameters are found so that the difference between the model and extracted features is
minimized. The main advantage of this phantom is that only one frame is required to determine translations, orientations,
and skew parameters of the scan plane with respect to the phantom. Experimental results with ocular imaging show the
ability to achieve alignment based on this method and its potential for medical applications.
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We propose the use of a time-of-flight (TOF) camera to obtain the patient's body contour in 3D guided imaging
reconstruction scheme in CT and C-arm imaging systems with truncated projection. In addition to pixel intensity, a TOF
camera provides the 3D coordinates of each point in the captured scene with respect to the camera coordinates.
Information from the TOF camera was used to obtain a digitized surface of the patient's body. The digitization points are
transformed to X-Ray detector coordinates by registering the two coordinate systems. A set of points corresponding to
the slice of interest are segmented to form a 2D contour of the body surface. Radon transform is applied to the contour to
generate the 'trust region' for the projection data. The generated 'trust region' is integrated as an input to augment the
projection data. It is used to estimate the truncated, unmeasured projections using linear interpolation. Finally the image
is reconstructed using the combination of the estimated and the measured projection data. The proposed method is
evaluated using a physical phantom. Projection data for the phantom were obtained using a C-arm system. Significant
improvement in the reconstructed image quality near the truncation edges was observed using the proposed method as
compared to that without truncation correction. This work shows that the proposed 3D guided CT image reconstruction
using a TOF camera represents a feasible solution to the projection data truncation problem.
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We have developed a combined image-guided and minimally invasive system for the delivery of therapy to the back of
the eye. It is composed of a short 4.5 mm diameter endoscope with a magnetic tracker embedded in the tip. In previous
work we have defined an optimized fiducial placement for accurate guidance to the back of the eye and are now moving
to system testing.
The fundamental difficulty in testing performance is establishing a target in a manner which closely mimics the
physiological task. We have to have a penetrable material which obscures line of sight, similar to the orbital fat. In
addition we need to have some independent measure of knowing when a target has been reached to compare to the ideal
performance. Lastly, the target cannot be rigidly attached to the skull phantom since the optic nerve lies buried in the
orbital fat.
We have developed a skull phantom with white cloth stellate balls supporting a correctly sized globe. Placed in
the white balls are red, blue, orange and yellow balls. One of the colored balls has been soaked in barium to make it
bright on CT. The user guides the tracked endoscope to the target as defined by the images and tells us its color. We
record task accuracy and time to target. We have tested this with 28 residents, fellows and attending physicians. Each
physician performs the task twice guided and twice unguided. Results will be presented.
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The advent and development of new imaging techniques and image-guidance have had a major impact on surgical
practice. These techniques attempt to allow the clinician to not only visualize what is currently visible, but also
what is beneath the surface, or function. These systems are often based on tracking systems coupled with
registration and visualization technologies. The accuracy and precision of the tracking systems, thus is critical in
the overall accuracy and precision of the image-guidance system. In this work the accuracy and precision of an
Aurora tracking system is assessed, using the technique specified in " novel technique for analysis of accuracy of
magnetic tracking systems used in image guided surgery." This analysis yielded a demonstration that accuracy is
dependent on distance from the tracker's field generator, and had an RMS value of 1.48 mm. The error has the
similar characteristics and values as the previous work, thus validating this method for tracker analysis.
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Sven Mersmann, Michael Müller, Alexander Seitel, Florian Arnegger, Ralf Tetzlaff, Julien Dinkel, Matthias Baumhauer, Bruno Schmied, Hans-Peter Meinzer, et al.
Proceedings Volume Medical Imaging 2011: Visualization, Image-Guided Procedures, and Modeling, 79642C (2011) https://doi.org/10.1117/12.878149
Augmented reality (AR) for enhancement of intra-operative images is gaining increasing interest in the field of
navigated medical interventions. In this context, various imaging modalities such as ultrasound (US), C-Arm
computed tomography (CT) and endoscopic images have been applied to acquire intra-operative information
about the patient's anatomy. The aim of this paper was to evaluate the potential of the novel Time-of-Flight
(ToF) camera technique as means for markerless intra-operative registration. For this purpose, ToF range data
and corresponding CT images were acquired from a set of explanted non-transplantable human and porcine
organs equipped with a set of marker that served as targets. Based on a rigid matching of the surfaces generated
from the ToF images with the organ surfaces generated from the CT data, the targets extracted from the
planning images were superimposed on the 2D ToF intensity images, and the target visualization error (TVE)
was computed as quality measure. Color video data of the same organs were further used to assess the TVE of a
previously proposed marker-based registration method. The ToF-based registration showed promising accuracy
yielding a mean TVE of 2.5±1.1 mm compared to 0.7±0.4 mm with the marker-based approach. Furthermore,
the target registration error (TRE) was assessed to determine the anisotropy in the localization error of ToF
image data. The TRE was 8.9± 4.7 mm on average indicating a high localization error in the viewing direction
of the camera. Nevertheless, the young ToF technique may become a valuable means for intra-operative surface
acquisition. Future work should focus on the calibration of systematic distance errors.
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We present a novel simulation system of blood flow through intracranial aneurysms including the interaction
between blood lumen and vessel tissue. It provides the means to estimate rupture risks by calculating the distribution
of pressure and shear stresses in the aneurysm, in order to support the planning of clinical interventions. So
far, this has only been possible with commercial simulation packages originally targeted at industrial applications,
whereas our implementation focuses on the intuitive integration into clinical workflow. Due to the time-critical
nature of the application, we exploit most efficient state-of-the-art numerical methods and technologies together
with high performance computing infrastructures (Austrian Grid). Our system builds a three-dimensional virtual
replica of the patient's cerebrovascular system from X-ray angiography, CT or MR images. The physician
can then select a region of interest which is automatically transformed into a tetrahedral mesh. The differential
equations for the blood flow and the wall elasticity are discretized via the finite element method (FEM), and the
resulting linear equation systems are handled by an algebraic multigrid (AMG) solver. The wall displacement
caused by the blood pressure is calculated using an iterative fluid-structure interaction (FSI) algorithm, and the
fluid mesh is deformed accordingly. First simulation results on measured patient geometries show good medical
relevance for diagnostic decision support.
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PURPOSE: The purpose of this study was to determine if medical trainees would benefit from augmented reality image
overlay and laser guidance in learning how to set the correct orientation of a needle for percutaneous facet joint
injection. METHODS: A total of 28 medical students were randomized into two groups: (1) The Overlay group received
a training session of four insertions with image and laser guidance followed by two insertions with laser overlay only;
(2) The Control group was trained by carrying out six freehand insertions. After the training session, needle trajectories
of two facet joint injections without any guidance were recorded by an electromagnetic tracker and were analyzed.
Number of successful needle placements, distance covered by needle tip inside the phantom and procedural time were
measured to evaluate performance. RESULTS: Number of successful placements was significantly higher in the Overlay
group compared to the Control group (85.7% vs. 57.1%, p = 0.038). Procedure time and distance covered inside
phantom have both been found to be less in the Overlay group, although not significantly. CONCLUSION: Training
with augmented reality image overlay and laser guidance improves the accuracy of facet joint injections in medical
students learning image-guided facet joint needle placement.
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Deflated lung's geometry simplifications effects on the accuracy of its biomechanical model used for its tumor
motion prediction are investigated. This investigation is necessary to determine the highest degree of
simplifications that can be incorporated in the lung's Finite Element (FE) model without compromising its ability
to predict tumor motion with reasonable accuracy. The simplifications involve neglecting the lung's airways in its
FE model. Such simplification is important to avoid unnecessary complications and to pave the way for fast tumor
location prediction during a lung tumor ablative procedure such as brachytherapy. One major factor, which may
affect the accuracy of such ablative procedures, is tumor motion resulting from lung tissue deformation caused by
respiration. Although the target lung is almost completely deflated during the procedure, tissue deformation
remains an issue due to diaphragm contact forces during respiration. In this investigation several numerical
experiments were conducted using different tumor and airway sizes and locations in conjunction with both elastic
and hyperelastic material models. Sensitivity of the tumor's motion prediction accuracy to the geometry
simplification was then presented as a function of airways' size relative to the tumor's size. FE analysis results
obtained for both material models suggest that tumor displacements due to surface contact forces are not very
sensitive to geometry simplification carried out by omitting airways as long as the airways size does not exceed the
tumor size.
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Patient motion can cause artifacts, which can lead to difficulty in interpretation. The purpose of this study is to create 3D
digital anthropomorphic phantoms which model the location of the structures of the chest and upper abdomen of human
volunteers undergoing a series of clinically relevant motions. The 3D anatomy is modeled using the XCAT phantom and
based on MRI studies. The NURBS surfaces of the XCAT are interactively adapted to fit the MRI studies. A detailed
XCAT phantom is first developed from an EKG triggered Navigator acquisition composed of sagittal slices with a 3 x 3
x 3 mm voxel dimension. Rigid body motion states are then acquired at breath-hold as sagittal slices partially covering
the thorax, centered on the heart, with 9 mm gaps between them. For non-rigid body motion requiring greater sampling,
modified Navigator sequences covering the entire thorax with 3 mm gaps between slices are obtained. The structures of
the initial XCAT are then adapted to fit these different motion states. Simultaneous to MRI imaging the positions of
multiple reflective markers on stretchy bands about the volunteer's chest and abdomen are optically tracked in 3D via
stereo imaging. These phantoms with combined position tracking will be used to investigate both imaging-data-driven
and motion-tracking strategies to estimate and correct for patient motion. Our initial application will be to cardiacperfusion
SPECT imaging where the XCAT phantoms will be used to create patient activity and attenuation distributions
for each volunteer with corresponding motion tracking data from the markers on the body-surface. Monte Carlo methods
will then be used to simulate SPECT acquisitions, which will be used to evaluate various motion estimation and
correction strategies.
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Microvascular flow phantoms were built to aid the development of a hemodynamic simulation model for treating
hepatocelluar carcinoma. The goal is to predict the blood flow routing for embolotherapy planning. Embolization is to
deliver agents (e.g. microspheres) to the vicinity of the tumor to obstruct blood supply and nutrients to the tumor,
targeting into 30 - 40 μm arterioles. Due to the size of the catheter, it has to release microspheres at an upper stream
location, which may not localize the blocking effect. Accurate anatomical descriptions of microvasculature will help to
conduct a reliable simulation and prepare a successful embolization strategy. Modern imaging devices can generate 3D
reconstructions with ease. However, with a fixed detector size, larger field of view yields lower resolution. Clinical CT
images can't be used to measure micro vessel dimensions, while micro-CT requires more acquisitions to reconstruct
larger vessels. A multi-tiered, montage 3D reconstruction method with hybrid-modality imagery is devised to minimize
the reconstruction effort. Regular CT is used for larger vessels and micro-CT is used for micro vessels. The montage
approach aims to stitch up images with different resolutions and orientations. A resolution-adaptable 3D image
registration is developed to assemble the images. We have created vessel phantoms that consist of several tiers of
bifurcating polymer tubes in reducing diameters, down to 25 μm. No previous work of physical flow phantom has
ventured into this small scale. Overlapping phantom images acquired from clinical CT and micro-CT are used to verify
the image registration fidelity.
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Organ motion due to respiration and contact with surgical instruments can significantly degrade the accuracy of image
guided surgery. In most applications the ensuing soft tissue deformations have to be compensated in order to register
preoperative planning data to the patient. Biomechanical models can be used to perform an accurate registration based
on sparse intraoperative sensor data. Using elasticity theory, the approach can be formulated as a boundary value
problem with displacement boundary conditions. In this paper, several models of the liver from the literature and a
new simplified model are evaluated with regards to their application to intraoperative soft tissue registration. We
construct finite element models of a liver phantom using the different material laws. Thereafter, typical deformation
pattern that occur during surgery are imposed by applying displacement boundary conditions. A comparative
numerical study shows that the maximal registration error of all non-linear models stays below 1.1mm, while the
linear model produces errors up to 3.9mm. It can be concluded that linear elastic models are not suitable for the
registration of the liver and that a geometrically non-linear formulation has to be used. Although the stiffness
parameters of the non-linear materials differ considerably, the calculated displacement fields are very similar. This
suggests that a difficult patient-specific parameterization of the model might not be necessary for intraoperative soft
tissue registration. We also demonstrate that the new simplified model achieves nearly the same registration accuracy
as complex quasi-linear viscoelastic models.
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We present on-going work on multi-resolution sulcal-separable meshing for approach-specific neurosurgery simulation, in
conjunction multi-grid and Total Lagrangian Explicit Dynamics finite elements. Conflicting requirements of interactive
nonlinear finite elements and small structures lead to a multi-grid framework. Implications for meshing are explicit control
over resolution, and prior knowledge of the intended neurosurgical approach and intended path. This information is used to
define a subvolume of clinical interest, within some distance of the path and the target pathology. Restricted to this
subvolume are a tetrahedralization of finer resolution, the representation of critical tissues, and sulcal separability
constraint for all mesh levels.
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This paper presents an approach to gallbladder shape comparison by using 3D shape modeling and decomposition. The
gallbladder models can be used for shape anomaly analysis and model comparison and selection in image guided robotic
surgical training, especially for laparoscopic cholecystectomy simulation. The 3D shape of a gallbladder is first
represented as a surface model, reconstructed from the contours segmented in CT data by a scheme of propagation based
voxel learning and classification. To better extract the shape feature, the surface mesh is further down-sampled by a
decimation filter and smoothed by a Taubin algorithm, followed by applying an advancing front algorithm to further
enhance the regularity of the mesh. Multi-scale curvatures are then computed on the regularized mesh for the robust
saliency landmark localization on the surface. The shape decomposition is proposed based on the saliency landmarks
and the concavity, measured by the distance from the surface point to the convex hull. With a given tolerance the 3D
shape can be decomposed and represented as 3D ellipsoids, which reveal the shape topology and anomaly of a
gallbladder. The features based on the decomposed shape model are proposed for gallbladder shape comparison, which
can be used for new model selection. We have collected 19 sets of abdominal CT scan data with gallbladders, some
shown in normal shape and some in abnormal shapes. The experiments have shown that the decomposed shapes reveal
important topology features.
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Pectus excavatum is the most common congenital deformity of the anterior chest wall, in which several ribs and the
sternum grow abnormally. Nowadays, the surgical correction is carried out in children and adults through Nuss technic.
This technic has been shown to be safe with major drivers as cosmesis and the prevention of psychological problems and
social stress. Nowadays, no application is known to predict the cosmetic outcome of the pectus excavatum surgical
correction. Such tool could be used to help the surgeon and the patient in the moment of deciding the need for surgery
correction. This work is a first step to predict postsurgical outcome in pectus excavatum surgery correction. Facing this
goal, it was firstly determined a point cloud of the skin surface along the thoracic wall using Computed Tomography
(before surgical correction) and the Polhemus FastSCAN (after the surgical correction). Then, a surface mesh was
reconstructed from the two point clouds using a Radial Basis Function algorithm for further affine registration between
the meshes. After registration, one studied the surgical correction influence area (SCIA) of the thoracic wall. This SCIA
was used to train, test and validate artificial neural networks in order to predict the surgical outcome of pectus excavatum
correction and to determine the degree of convergence of SCIA in different patients. Often, ANN did not converge to a
satisfactory solution (each patient had its own deformity characteristics), thus invalidating the creation of a mathematical
model capable of estimating, with satisfactory results, the postsurgical outcome.
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Since MR image intensities do not possess a tissue specific numeric meaning, even in images acquired for the
same subject, on the same scanner, for the same body region, by using the same pulse sequence, it is important
to transform the image scale into a standard intensity scale so that, for the same body region, intensities are
similar. The lack of a standard image intensity scale in MRI leads to many difficulties in tissue characterizability,
image display, and analysis, including image segmentation and registration. The influence of standardization
on these tasks has been documented well; however, how intensity non-standardness may affect the automatic
recognition of anatomical structures for image segmentation has not been studied. Motivated from the study
that we previously presented in SPIE Medical Imaging Conference 2010,1, 2 in this study, we analyze the effects
of intensity standardization on anatomical object recognition. A set of 31 scenarios of multiple objects from
the ankle complex included in the model, plus seven different realistic levels of non-standardness introduced are
considered for evaluation. The experimental results imply that, intensity variation among scenes in an ensemble
- a particular characteristic of the behavior of non-standardness - degrades object recognition performance.
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Recently, image-based computational fluid dynamic simulations (CFD) have been proposed to investigate the local
hemodynamics inside human cerebral aneurysms. It is suggested that the knowledge of the computed three-dimensional
flow fields can be used to assist clinical risk assessment and treatment decision making.
However, the reliability of CFD for accurately representing the human cerebral blood flow is difficult to assess due to
the impossibility of ground truth measurements. A recently proposed virtual angiography method has been used to
indirectly validate CFD results by comparing virtually constructed and clinically acquired angiograms. However, the
validations are not yet comprehensive as they lack either from patient-specific boundary conditions (BCs) required for
CFD simulations or from quantitative comparison methods.
In this work, a simulation pipeline is built up including image-based geometry reconstruction, CFD simulations
solving the dynamics of blood flow and contrast agent (CA), and virtual angiogram generation. In contrast to previous
studies, the patient-specific blood flow rates obtained by transcranial color coded Doppler (TCCD) ultrasound are used to
impose CFD BCs. Quantitative measures are defined to thoroughly evaluate the correspondence between the clinically
acquired and virtually constructed angiograms, and thus, the reliability of CFD simulations. Exemplarily, two patient
cases are presented.
Close similarities are found in terms of spatial and temporal variations of CA distribution between acquired and
virtual angiograms. Besides, for both patient cases, discrepancies of less than 15% are found for the relative root mean
square errors (rRMSE) in time intensity curve (TIC) comparisons from selected characteristic positions.
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Traditional bone atlas modelling is carried out using linear methods such as PCA. Such linear models use a
mean shape and principal modes to represent the atlas. A new shape, which is a high dimensional data vector,
is then described using this mean and a weighted combination of the principal modes. The use of alternate
methods for modelling statistical atlases have not been explored very much. Recently, there has been a lot of
new work in the areas of multilinear modelling and nonlinear modelling. They present new ways of modelling
high dimensional data. In this work, we compare and contrast several linear, multilinear and nonlinear methods
for bone atlas modelling.
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The multimodal fusion of spatially tracked real-time ultrasound (US) with a prior CT scan has demonstrated clinical
utility, accuracy, and positive impact upon clinical outcomes when used for guidance during biopsy and radiofrequency
ablation in the treatment of cancer. Additionally, the combination of CT-guided procedures with positron emission
tomography (PET) may not only enhance navigation, but add valuable information regarding the specific location and
volume of the targeted masses which may be invisible on CT and US. The accuracy of this fusion depends on reliable,
reproducible registration methods between PET and CT. This can avoid extensive manual efforts to correct registration
which can be long and tedious in an interventional setting. In this paper, we present a registration workflow for
PET/CT/US fusion by analyzing various image metrics based on normalized mutual information and cross-correlation,
using both rigid and affine transformations to automatically align PET and CT. Registration is performed between the
CT component of the prior PET-CT and the intra-procedural CT scan used for navigation to maximize image
congruence. We evaluate the accuracy of the PET/CT registration by computing fiducial and target registration errors
using anatomical landmarks and lesion locations respectively. We also report differences to gold-standard manual
alignment as well as the root mean square errors for CT/US fusion. Ten patients with prior PET/CT who underwent
ablation or biopsy procedures were selected for this study. Studies show that optimal results were obtained using a crosscorrelation
based rigid registration with a landmark localization error of 1.1 +/- 0.7 mm using a discrete graphminimizing
scheme. We demonstrate the feasibility of automated fusion of PET/CT and its suitability for multi-modality
ultrasound guided navigation procedures.
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Registration of preoperative CT data to intra-operative video images is necessary not only to compare the outcome
of the vocal fold after surgery with the preplanned shape but also to provide the image guidance for fusion of all imaging
modalities. We propose a 2D-3D registration method using gradient-based mutual information. The 3D CT scan is
aligned to 2D endoscopic images by finding the corresponding viewpoint between the real camera for endoscopic images
and the virtual camera for CT scans. Even though mutual information has been successfully used to register different
imaging modalities, it is difficult to robustly register the CT rendered image to the endoscopic image due to varying light
patterns and shape of the vocal fold. The proposed method calculates the mutual information in the gradient images as
well as original images, assigning more weight to the high gradient regions. The proposed method can emphasize the
effect of vocal fold and allow a robust matching regardless of the surface illumination. To find the viewpoint with
maximum mutual information, a downhill simplex method is applied in a conditional multi-resolution scheme which
leads to a less-sensitive result to local maxima. To validate the registration accuracy, we evaluated the sensitivity to
initial viewpoint of preoperative CT. Experimental results showed that gradient-based mutual information provided
robust matching not only for two identical images with different viewpoints but also for different images acquired before
and after surgery. The results also showed that conditional multi-resolution scheme led to a more accurate registration
than single-resolution.
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In navigated liver surgery it is an important task to align intra-operative data to pre-operative planning data.
This work describes a method to register pre-operative 3D-CT-data to tracked intra-operative 2D US-slices.
Instead of reconstructing a 3D-volume out of the two-dimensional US-slice sequence we directly apply the registration
scheme to the 2D-slices. The advantage of this approach is manyfold. We circumvent the time consuming
compounding process, we use only known information, and the complexity of the scheme reduces drastically. As
the liver is a non-rigid organ, we apply non-linear techniques to take care of deformations occurring during the
intervention. During the surgery, computing time is a crucial issue. As the complexity of the scheme is proportional
to the number of acquired slices, we devise a scheme which starts out by selecting a few "key-slices" to
be used in the non-linear registration scheme. This step is followed by multi-level/multi-scale strategies and fast
optimization techniques. In this abstract we briefly describe the new method and show first convincing results.
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Motivation: In prostate brachytherapy, real-time dosimetry would be ideal to allow for rapid evaluation of the implant
quality intra-operatively. However, such a mechanism requires an imaging system that is both real-time and which
provides, via multiple C-arm fluoroscopy images, clear information describing the three-dimensional position of the
seeds deposited within the prostate. Thus, accurate tracking of the C-arm poses proves to be of critical importance to the
process. Methodology: We compute the pose of the C-arm relative to a stationary radiographic fiducial of known
geometry by employing a hybrid registration framework. Firstly, by means of an ellipse segmentation algorithm and a
2D/3D feature based registration, we exploit known FTRAC geometry to recover an initial estimate of the C-arm pose.
Using this estimate, we then initialize the intensity-based registration which serves to recover a refined and accurate
estimation of the C-arm pose. Results: Ground-truth pose was established for each C-arm image through a published and
clinically tested segmentation-based method. Using 169 clinical C-arm images and a ±10° and ±10 mm random
perturbation of the ground-truth pose, the average rotation and translation errors were 0.68° (std = 0.06°) and 0.64 mm
(std = 0.24 mm). Conclusion: Fully automated C-arm pose estimation using a 2D/3D hybrid registration scheme was
found to be clinically robust based on human patient data.
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This paper provides a comparison of spline-based registration methods applied to register interventional Trans Rectal Ultrasound (TRUS) and pre-acquired Magnetic Resonance (MR) prostate images for needle guided prostate biopsy. B-splines and Thin-plate Splines (TPS) are the most prevalent spline-based approaches to achieve deformable registration. Pertaining to the strategic selection of correspondences for the TPS registration, we use an automatic method already proposed in our previous work to generate correspondences in the MR and US prostate images. The method exploits the prostate geometry with the principal components of the segmented prostate as the underlying framework and involves a triangulation approach. The correspondences are generated with successive refinements and Normalized Mutual Information (NMI) is employed to determine the
optimal number of correspondences required to achieve TPS registration. B-spline registration with successive grid refinements are consecutively applied for a significant comparison of the impact of the strategically chosen correspondences on the TPS registration against the uniform B-spline control grids. The experimental results
are validated on 4 patient datasets. Dice Similarity Coefficient (DSC) is used as a measure of the registration accuracy. Average DSC values of 0.97±0.01 and 0.95±0.03 are achieved for the TPS and B-spline registrations respectively. B-spline registration is observed to be more computationally expensive than the TPS registration
with average execution times of 128.09 ± 21.7 seconds and
62.83 ± 32.77 seconds respectively for images with maximum width of 264 pixels and a maximum height of 211 pixels.
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Total Hip Replacement (THR) has become a common surgical procedure in recent years, as a result of increasing
aging population with osteoarthritis of the hip joint. Localization of the pelvic anatomical coordinate system
(PaCS) is a critical step in accurate placement of the femur prosthesis in the acetabulum in THR. Intra-operative
ultrasound (US) imaging can provide a radiation-free navigation system for localization of the PaCS. However,
US images are noisy and cannot provide any anatomical information beneath the bone surface due to the total
reflection of US beam at the bone-soft tissue interface. A solution to this problem is to fuse intra-operative
US with pre-operative imaging or a statistical shape model (SSM) of the pelvis. Here, we propose a multi-slice
to volume intensity-based registration of the pelvic SSM to a sparse set of 2D US images in order to localize
the PaCS in the US. In this registration technique, a set of 2D slices are extracted from a pelvic SSM using
the approximate location and orientation of their corresponding 2D US images. During the registration, the
comparison between the SSM slices and the US images is made using an ultrasound simulation technique and
a correlation-based similarity metric. We demonstrate the feasibility of our proposed approach in localizing
the PaCS on five patient-based phantoms. These results indicate the necessity of including pubic symphysis
landmarks in the 2D US slices in order to have a precise estimation of the PaCS.
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We present a 3D non-rigid registration algorithm for the potential use in combining PET/CT and transrectal ultrasound
(TRUS) images for targeted prostate biopsy. Our registration is a hybrid approach that simultaneously optimizes the
similarities from point-based registration and volume matching methods. The 3D registration is obtained by minimizing
the distances of corresponding points at the surface and within the prostate and by maximizing the overlap ratio of the
bladder neck on both images. The hybrid approach not only capture deformation at the prostate surface and internal
landmarks but also the deformation at the bladder neck regions. The registration uses a soft assignment and deterministic
annealing process. The correspondences are iteratively established in a fuzzy-to-deterministic approach. B-splines are
used to generate a smooth non-rigid spatial transformation. In this study, we tested our registration with pre- and postbiopsy
TRUS images of the same patients. Registration accuracy is evaluated using manual defined anatomic landmarks,
i.e. calcification. The root-mean-squared (RMS) of the difference image between the reference and floating images was
decreased by 62.6±9.1% after registration. The mean target registration error (TRE) was 0.88±0.16 mm, i.e. less than 3
voxels with a voxel size of 0.38×0.38×0.38 mm3 for all five patients. The experimental results demonstrate the
robustness and accuracy of the 3D non-rigid registration algorithm.
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We present a parallel implementation of a statistical shape model registration to 3D ultrasound images of the
lumbar vertebrae (L2-L4). Covariance Matrix Adaptation Evolution Strategy optimization technique, along
with Linear Correlation of Linear Combination similarity metric have been used, to improve the robustness and
capture range of the registration approach. Instantiation and ultrasound simulation have been implemented on
a graphics processing unit for a faster registration. Phantom studies show a mean target registration error of 3.2
mm, while 80% of all the cases yield target registration error of below 3.5 mm.
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We describe a technique to build a soft-walled colon phantom that provides realistic lumen anatomy in computed
tomography (CT) images. The technique begins with the geometry of a human colon measured during CT colonography
(CTC). The three-dimensional air-filled colonic lumen is segmented and then replicated using stereolithography (SLA).
The rigid SLA model includes large-scale features (e.g., haustral folds and tenia coli bands) down to small-scale features
(e.g., a small pedunculated polyp). Since the rigid model represents the internal air-filled volume, a highly-pliable
silicone polymer is painted onto the rigid model. This thin layer of silicone, when removed, becomes the colon wall.
Small 3 mm diameter glass beads are affixed to the outer wall. These glass beads show up with high intensity in CT
scans and provide a ground truth for evaluating performance of algorithms designed to register prone and supine CTC
data sets. After curing, the silicone colon wall is peeled off the rigid model. The resulting colon phantom is filled with
air and submerged in a water bath. CT images and intraluminal fly-through reconstructions from CTC scans of the colon
phantom are compared against patient data to demonstrate the ability of the phantom to simulate a human colon.
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In this paper, we estimate the deformations induced on soft tissues by the rigid independent movements of
hard objects and create an admixture of rigid and elastic adaptive image registration transformations. By
automatically segmenting and independently estimating the movement of rigid objects in 3D images, we can
maintain rigidity in bones and hard tissues while appropriately deforming soft tissues. We tested our algorithms
on 20 pairs of 3D MRI datasets pertaining to a kinematic study of the flexibility of the ankle complex of normal
feet as well as ankles affected by abnormalities in foot architecture and ligament injuries. The results show
that elastic image registration via rigid object-induced deformation outperforms purely rigid and purely nonrigid
approaches.
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3D-2D registration is a fundamental task in image guided interventions. Due to the physics of
the X-ray imaging, however, traditional point based methods meet new challenges, where the local
point features are indistinguishable, creating difficulties in establishing correspondence between 2D
image feature points and 3D model points. In this paper, we propose a novel method to accomplish
3D-2D registration without known correspondences. Given a set of 3D and 2D unmatched points,
this is achieved by introducing correspondence probabilities that we model as a mixture model. By
casting it into the expectation conditional maximization framework, without establishing one-to-one
point correspondences, we can iteratively refine the registration parameters. The method has been
tested on 100 real X-ray images. The experiments showed that the proposed method accurately
estimated the rotations (< 1°) and in-plane (X-Y plane) translations (< 1 mm).
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In this paper, we propose a two-stage labeling method of large biomedical datasets through a parallel approach
in a single GPU. Diagnostic methods, structures volume measurements, and visualization systems are of major
importance for surgery planning, intra-operative imaging and image-guided surgery. In all cases, to provide
an automatic and interactive method to label or to tag different structures contained into input data becomes
imperative. Several approaches to label or segment biomedical datasets has been proposed to discriminate
different anatomical structures in an output tagged dataset. Among existing methods, supervised learning
methods for segmentation have been devised to easily analyze biomedical datasets by a non-expert user. However,
they still have some problems concerning practical application, such as slow learning and testing speeds. In
addition, recent technological developments have led to widespread availability of multi-core CPUs and GPUs,
as well as new software languages, such as NVIDIA's CUDA and OpenCL, allowing to apply parallel programming
paradigms in conventional personal computers.
Adaboost classifier is one of the most widely applied methods for labeling in the Machine Learning community.
In a first stage, Adaboost trains a binary classifier from a set of pre-labeled samples described by a set of
features. This binary classifier is defined as a weighted combination of weak classifiers. Each weak classifier is a
simple decision function estimated on a single feature value. Then, at the testing stage, each weak classifier is
independently applied on the features of a set of unlabeled samples.
In this work, we propose an alternative representation of the Adaboost binary classifier. We use this proposed
representation to define a new GPU-based parallelized Adaboost testing stage using OpenCL. We provide
numerical experiments based on large available data sets and we compare our results to CPU-based strategies
in terms of time and labeling speeds.
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Atrial fibrillation is a common heart arrhythmia, and can be effectively treated with ablation. Ablation planning
requires 3D models of the patient's left atrium (LA) and/or right atrium (RA), therefore an automatic segmentation
procedure to retrieve these models is desirable. In this study, we investigate the use of advanced level
set segmentation approaches to automatically segment RA in magnetic resonance angiographic (MRA) volume
images. Low contrast to noise ratio makes the boundary between the RA and the nearby structures nearly indistinguishable.
Therefore, pure data driven segmentation approaches such as watershed and ChanVese methods
are bound to fail. Incorporating training shapes through PCA modeling to constrain the segmentation is one
popular solution, and is also used in our segmentation framework. The shape parameters from PCA are optimized
with a global histogram based energy model. However, since the shape parameters span a much smaller
space, it can not capture fine details of the shape. Therefore, we employ a second refinement step after the shape
based segmentation stage, which follows closely the recent work of localized appearance model based techniques.
The local appearance model is established through a robust point tracking mechanism and is learned through
landmarks embedded on the surface of training shapes. The key contribution of our work is the combination
of a statistical shape prior and a localized appearance prior for level set segmentation of the right atrium from
MRA. We test this two step segmentation framework on porcine RA to verify the algorithm.
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We are developing a molecular image-directed, 3D ultrasound-guided, targeted biopsy system for improved detection of
prostate cancer. In this paper, we propose an automatic 3D segmentation method for transrectal ultrasound (TRUS)
images, which is based on multi-atlas registration and statistical texture prior. The atlas database includes registered
TRUS images from previous patients and their segmented prostate surfaces. Three orthogonal Gabor filter banks are
used to extract texture features from each image in the database. Patient-specific Gabor features from the atlas database
are used to train kernel support vector machines (KSVMs) and then to segment the prostate image from a new patient.
The segmentation method was tested in TRUS data from 5 patients. The average surface distance between our method
and manual segmentation is 1.61 ± 0.35 mm, indicating that the atlas-based automatic segmentation method works well
and could be used for 3D ultrasound-guided prostate biopsy.
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In this paper, we report a novel three-dimensional (3D) wound imaging system (hardware and software) under
development at Technest Inc. System design is aimed to perform accurate 3D measurement and modeling of a wound
and track its healing status over time. Accurate measurement and tracking of wound healing enables physicians to assess,
document, improve, and individualize the treatment plan given to each wound patient. In current wound care practices,
physicians often visually inspect or roughly measure the wound to evaluate the healing status. This is not an optimal
practice since human vision lacks precision and consistency. In addition, quantifying slow or subtle changes through
perception is very difficult. As a result, an instrument that quantifies both skin color and geometric shape variations
would be particularly useful in helping clinicians to assess healing status and judge the effect of hyperemia, hematoma,
local inflammation, secondary infection, and tissue necrosis. Once fully developed, our 3D imaging system will have
several unique advantages over traditional methods for monitoring wound care: (a) Non-contact measurement; (b) Fast
and easy to use; (c) up to 50 micron measurement accuracy; (d) 2D/3D Quantitative measurements;(e) A handheld
device; and (f) Reasonable cost (< $1,000).
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Public visualization of high quality medical information has been wildly available since the creation of the Visible
Human Project in the late 90´s. We discuss the extraction of information from 3D volumes along curved slices with
emphasis on those that can be displayed on the plane without deformation. Special attention is given to a dental volume
containing the sixteen teeth of the upper human jaw. We review several approaches to display information along curved
slices contained within the 3D data set.
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A unified framework for voxel classification and triangulation for medical images is presented. Given volumetric
data, each voxel is labeled by a two-dimensional classification function based on voxel intensity and gradient. A
modified Constrained Elastic Surface Net is integrated into the classification function, allowing the surface mesh
to be generated in a single step. The modification to the Constrained Elastic Surface Net includes additional
triangulation cases which reduce visual artifacts, and a surface-node relaxation criterion based on linear regression
which improves visual appearance and preserves the enclosed volume. By carefully designing the two-dimensional
classification function, surface meshes for different anatomical structures can be generated in a single process.
This framework is implemented on the GPU, allowing rendition of the voxel classification to be visualized in
near real-time.
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Fiber tracking is one of the clinically most well-established analysis techniques for Diffusion Tensor Imaging data (DTI).
It facilitates the reconstruction of anatomically known white matter structures by tracing trajectories on a tensor field
obtained from diffusion weighted MR images. A crucial step when using this technique is the placement and shape of
regions-of-interest (ROIs) to identify the structures in question. Typically, free-hand contours or simple geometric shapes
like rectangles are placed in regions, where a given structure can be identified using the color coded DTI representation.
However, such approaches result in a high variability of the resulting tracts and usually require additional filtering and
placement of multiple ROIs. Also, the generation of accurate ROIs using a free-hand tool requires a significant amount
of interaction time. We present a method which allows for interactive generation of anatomically meaningful ROIs for
DTI fiber tracking based on geometric similarities of the underlying tensor field. The method works similar to the magicwand
tool known from image editing software tools to create reasonable, fully image based ROIs using a single mouseclick.
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The Insight Segmentation and Registration Toolkit (ITK) is a long-established, software package used for image
analysis, visualization, and image-guided surgery applications. This package is a collection of C++ libraries, that
can pose usability problems for users without C++ programming experience. To bridge the gap between the
programming complexities and the required learning curve of ITK, we present a higher-level visual programming
environment that represents ITK methods and classes by wrapping them into "blocks" within MATLAB's visual
programming environment, Simulink. These blocks can be connected to form workflows: visual schematics that
closely represent the structure of a C++ program. Due to the heavily C++ templated nature of ITK, direct
interaction between Simulink and ITK requires an intermediary to convert their respective datatypes and allow
intercommunication. We have developed a "Virtual Block" that serves as an intermediate wrapper around the
ITK class and is responsible for resolving the templated datatypes used by ITK to native types used by Simulink.
Presently, the wrapping procedure for SimITK is semi-automatic in that it requires XML descriptions of the
ITK classes as a starting point, as this data is used to create all other necessary integration files. The generation
of all source code and object code from the XML is done automatically by a CMake build script that yields
Simulink blocks as the final result. An example 3D segmentation workflow using cranial-CT data as well as a
3D MR-to-CT registration workflow are presented as a proof-of-concept.
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The low-cost and minimum health risks associated with ultrasound (US) have made ultrasonic imaging a widely
accepted method to perform diagnostic and image-guided procedures. Despite the existence of 3D ultrasound probes,
most analysis and diagnostic procedures are done by studying the B-mode images. Currently, multiple ultrasound
probes include 6-DOF sensors that can provide positioning information. Such tracking information can be used to
reconstruct a 3D volume from a set of 2D US images. Recent advances in ultrasound imaging have also shown that,
directly from the streaming radio frequency (RF) data, it is possible to obtain additional information of the anatomical
region under consideration including the elasticity properties.
This paper presents a generic framework that takes advantage of current graphics hardware to create a low-latency
system to visualize streaming US data while combining multiple tissue attributes into a single illustration. In particular,
we introduce a framework that enables real-time reconstruction and interactive visualization of streaming data while
enhancing the illustration with elasticity information. The visualization module uses two-dimensional transfer functions
(2D TFs) to more effectively fuse and map B-mode and strain values into specific opacity and color values. On
commodity hardware, our framework can simultaneously reconstruct, render, and provide user interaction at over 15
fps. Results with phantom and real-world medical datasets show the advantages and effectiveness of our technique with
ultrasound data. In particular, our results show how two-dimensional transfer functions can be used to more effectively
identify, analyze and visualize lesions in ultrasound images.
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Medical Imaging Software (MIS) found in research and in clinical practice, such as in Picture and Archiving
Communication Systems (PACS) and Radiology Information Systems (RIS), has not been able to take full
advantage of the Internet as a deployment platform. MIS is usually tightly coupled to algorithms that have
substantial hardware and software requirements. Consequently, MIS is deployed on thick clients which usually
leads project managers to allocate more resources during the deployment phase of the application than the
resources that would be allocated if the application were deployed through a web interface.To minimize the costs
associated with this scenario, many software providers use or develop plug-ins to provide the delivery platform
(internet browser) with the features to load, interact and analyze medical images. Nevertheless there has not
been a successful standard means to achieve this goal so far.
This paper presents a study of WebGL as an alternative to plug-in development for efficient rendering of 3D
medical models and DICOM images. WebGL is a technology that enables the internet browser to have access
to the local graphics hardware in a native fashion. Because it is based in OpenGL, a widely accepted graphic
industry standard, WebGL is being implemented in most of the major commercial browsers.
After a discussion on the details of the technology, a series of experiments are presented to determine the
operational boundaries in which WebGL is adequate for MIS. A comparison with current alternatives is also
addressed. Finally conclusions and future work are discussed.
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Ray casting is the most frequently used algorithm in direct volume rendering for displaying medical data, although it is
computationally very expensive. Recent hardware improvements have allowed ray casting to be used in real-time,
however, there is room for performance gains to take advantage of the recent development of general-purpose graphical
processing units (GPU). The purpose of this paper is to implement the volume ray casting with the Compute Unified
Device Architecture (CUDA) to obtain higher rendering performance. The experimental results show that the new
algorithm is up to 15 times faster than the conventional CPU-based ray casting algorithm.
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Exploded view generation for volumetric object is a useful method in surgical simulation, but it is very hard to perform
real-time operation. We present an interactive method to determine interesting regions and to render a scene with varying
volume datasets in real-time. In general, since conventional methods are designed to solve the problem of occlusion of
sub-volumes, they did not consider performance. Especially, exploded view generation methods are difficult to render a
scene in real-time even in the case of exploiting highly optimized method. Because they perform volume rendering after
defining rules to split an original volume and constraints to order sub-volumes. We present an interactive cutting
operation using GPU-based parallel processing and real-time rendering using block-based re-rendering method.
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