In this paper, frequency-domain endoscopic diffuse optical tomography image reconstruction algorithm based on dual-modulation-frequency and dual-points source diffuse equation is investigated for the reconstruction of the optical parameters including the absorption and reducing scattering coefficients. The forward problem is solved by the finite element method based on the frequency domain diffuse equation (FD-DE) for dual-points source approximation and multi-modulation-frequency. In the image reconstruction, a multi-modulation-frequency Newton-Raphson algorithm is applied to obtain the solution. To further improve the image accuracy and quality, a method based on the region of interest (ROI) is applied on the above procedures. The simulation is performed in the tubular model to verify the validity of the algorithm. Results show that the FD-DE with dual-points source approximate is more accuracy at shorter source-detector separation. The reconstruction with dual-modulation-frequency improves the image accuracy and quality compared to the results with single-modulation-frequency and triple-modulation-frequency method. The peak optical coefficients in ROI (ROI_max) are almost equivalent to the true optical coefficients with the relative error less than 6.67%. The full width at half maximum (FWHM) achieves 82% of the true radius. The contrast-to-noise ratio (CNR) and image coefficient(IC) is 5.678 and 26.962, respectively. Additionally, the results with the method based on ROI show that the ROI_max is equivalent to the true value. The FWHM can improve by 88% of the true radius. The CNR and IC is improved over 7.782 and 45.335, respectively.
In this paper, we constructed a continuous wave non-contact diffuse optical tomography (DOT) system for the dense sampling of both the illumination and detection by using a laser raster scanning and a CCD-based data acquisition. For dealing with the large size of measurement data obtained from the non-contact system, a fast tomographic image reconstruction scheme for reconstructing the absorption coefficient of a slab is developed. The proposed algorithm is carried out with the spatial-frequency encoding in both the measurement and the image spaces, and involves a strategy for selecting the useful spatial frequency based on the transfer function of tissue. Dense sampling offers an effective way of improving the image reconstruction performances and the developed algorithm is expected to considerably reduce the calculation time for reconstruction whilst retain the quality of the reconstructed images. Reconstructions from the experimental data show that the inversion scheme developed in this paper can get an absorption image within 20s, which has higher quality than those reconstructed in several hours by using the conventional reconstruction method.
In the non-invasive brain imaging with near-infrared light, precise head model is of great significance to the forward model and the image reconstruction. To deal with the individual difference of human head tissues and the problem of the irregular curvature, in this paper, we extracted head structure with Mimics software from the MRI image of a volunteer. This scheme makes it possible to assign the optical parameters to every layer of the head tissues reasonably and solve the diffusion equation with the finite-element analysis. During the solution of the inverse problem, a semi-3D reconstruction algorithm is adopted to trade off the computation cost and accuracy between the full 3-D and the 2-D reconstructions. In this scheme, the changes in the optical properties of the inclusions are assumed either axially invariable or confined to the imaging plane, while the 3-D nature of the photon migration is still retained. This therefore leads to a 2-D inverse issue with the matched 3-D forward model. Simulation results show that comparing to the 3-D reconstruction algorithm, the Semi-3D reconstruction algorithm cut 27% the calculation time consumption.
To reduce the cost of near-infrared endoscopic image equipment and the reconstruction time, a measurement method
based on the effective detection area is proposed and the corresponding algorithm which simultaneously reconstructs the
absorption coefficient and the reduced scattering coefficient is developed. First, the effective detection area is
investigated with the Monte Carlo simulation. Secondly, the image reconstruction algorithm based on the effective
detection area is studied. The Jacobin matrix is built by combining the adjoint method with the modified Generalized
Pulse Spectrum Technique and calibrated by the maximum of its absolute value. The Generalized Minimal Residual
Krylov method is used to obtain the iterative update factor. Finally, the impact of the number of measured points in the
effective detection area on the reconstructed results is discussed, and the robustness of the algorithm to noise and
cross-talk are verified by the simulated test data. The results show that the reconstructed algorithm based on the effective
detection area has equivalent accuracy to the traditional ones. The fidelity of reconstructed absorption and reduced
scattering coefficients can be 80%, respectively. The scales and positions of the reconstructed lesions are both correspond
to the true and the reconstruction time is reduced by half. The optimal number of sources and detectors is 16 depending
on the scale of the simulation model. The detection using the effective detection area and the developed reconstruction
algorithm will promote the development of diffuse optical tomography which is applied to cervical and other tubular
organs.
This article aims at the development of the fast inverse Monte Carlo (MC) simulation for the reconstruction of
optical properties (absorption coefficient μs and scattering coefficient μs) of cylindrical tissue, such as a cervix,
from the measurement of near infrared diffuse light on frequency domain. Frequency domain information (amplitude
and phase) is extracted from the time domain MC with a modified method. To shorten the computation time in
reconstruction of optical properties, efficient and fast forward MC has to be achieved. To do this, firstly, databases of
the frequency-domain information under a range of μa and μs were pre-built by combining MC simulation with
Lambert-Beer's law. Then, a double polynomial model was adopted to quickly obtain the frequency-domain
information in any optical properties. Based on the fast forward MC, the optical properties can be quickly obtained in a
nonlinear optimization scheme. Reconstruction resulting from simulated data showed that the developed inverse MC
method has the advantages in both the reconstruction accuracy and computation time. The relative errors in
reconstruction of the μs and μs are less than ±6% and ±12% respectively, while another coefficient (μs or μs) is in
a fixed value. When both μs and μs are unknown, the relative errors in reconstruction of the reduced scattering
coefficient and absorption coefficient are mainly less than ±10% in range of 45< μs <80 cm-1 and 0.25< a μ <0.55 cm-1.
With the rapid reconstruction strategy developed in this article the computation time for reconstructing one set of the
optical properties is less than 0.5 second. Endoscopic measurement on two tubular solid phantoms were also carried out
to evaluate the system and the inversion scheme. The results demonstrated that less than 20% relative error can be
achieved.
Optical diagnostics has the potential to provide real-time diagnosis of tissue noninvasively, and many optical
diagnostic techniques are receiving extensive attention and being developed. Frequency domain (FD) near-infrared
diffuse spectroscopy (NIRS) is one of the three common techniques in NIRS field. Generally, a FD system modulates
the light intensity in radio frequency and measures the amplitude attenuation and phase delay of the diffused light using
heterodyne detection.
This article deals with the method for eliminating or calibrating both coupling factor and the intrinsic parameters of
the measurement system, which include the intrinsic amplitude attenuation and intrinsic phase delay. Several calibration
methods are proposed, namely, calibration with standard phantom, calibration based on multiple source-detector
separations (SDS), and calibration with the combination of standard phantom and multiple SDS.
Two solid tubular phantoms with known optical properties are adopted to evaluate the proposed calibration
methods. Endoscopic measurements on the phantoms were carried on to obtain the amplitude attenuation and phase
delay while Monte Carlo simulation was employed to calculate the "real" ones. Results show that the calibration
method with the combination of standard phantom and multiple SDS gets the minimum relative error of amplitude.
This article aims at the optical property (absorption coefficient and scatter coefficient) reconstruction from the
frequency-domain (FD) near-infrared diffuse measurement on small tissues, such as a cervix, for which inverse Monte
Carlo (MC) simulation is the suitable choice. To achieve the fast and accurate reconstruction based on the inverse Monte
Carlo simulation, following techniques were adopted. First, in the forward calculation, a database, which include the
frequency-domain information calculated from MC simulation for a series of optical parameters of tissue, were
established with fast methods. Then, in the reconstruction procedure, Levenberg-Marquardt (L-M) optimization was
adopted and Multiple Polynomial Regression (MPR) method was used to rapidly get the FD information at any optical
properties by best fitting the curved surface formed by the above database. At Last, in the reconstruction, to eliminate the
influence of the initial guess of optical properties on the reconstruction accuracy, cluster analysis method was introduced
into L-M reconstruction algorithm to determine the region of the initial guess. The reconstruction algorithm was
demonstrated with simulation data. The results showed that it takes less than 0.5s to reconstruction one set of optical
properties. The average relative error from the reconstruction algorithm joined with cluster analysis is 10% lower than
that without cluster analysis.
This article aims at the development of the fast inverse Monte Carlo (MC) simulation for the reconstruction of optical properties (absorption coefficient and scattering coefficient ) of cylindrical tissue [1], such as a cervix, from the measurement of near infrared diffuse light on frequency domain. Frequency domain information (amplitude and phase) is extracted from the time domain MC with a modified method. To shorten the computation time in reconstruction of optical properties, efficient and fast forward MC has to be achieved. To do this, firstly, databases of the frequency-domain information under a range of μa and μs were pre-built by combining MC simulation with Lambert-Beer's law. Then, a double polynomial model was adopted to quickly obtain the frequency-domain information in any optical properties. Based on the fast forward MC, the optical properties can be quickly obtained in a nonlinear optimization scheme. Reconstruction resulting from simulated data showed that the developed inverse MC method has the advantages in both the reconstruction accuracy and computation time. The relative errors in reconstruction of the μa and μs are less than ±6% and ±12% respectively, while another coefficient (μa or μs) is in a fixed value. When both μa and μs are unknown, the relative errors in reconstruction of the reduced scattering coefficient and absorption coefficient are mainly less than ±10% in range of 45 < μs <80 cm-1 and 0.25< μa <0.55 cm-1. With the rapid reconstruction strategy developed in this article the computation time for reconstructing one set of the optical properties is less than 0.5 second.
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