HARMONI is a visible and near-IR integral field spectrograph, providing the E-ELT's spectroscopic capability at first
light. It obtains simultaneous spectra of 32000 spaxels, at a range of resolving powers from R~4000 to R~20000,
covering the wavelength range from 0.47 to 2.45 μm. The 256 × 128 spaxel field of view has four different plate scales,
with the coarsest scale (40 mas) providing a 5″ × 10″ FoV, while the finest scale is a factor of 10 finer (4mas).
We describe the opto-mechanical design of HARMONI, prior to the start of preliminary design, including the main subsystems
- namely the image de-rotator, the scale-changing optics, the splitting and slicing optics, and the spectrographs.
We also present the secondary guiding system, the pupil imaging optics, the field and pupil stops, the natural guide star
wavefront sensor, and the calibration unit.
Dario Sosa-Cabrera, Antonio Tristan-Vega, Gonzalo Vegas-Sanchez-Ferrero, Javier Gonzalez-Fernandez, Luis Gomez-Deniz, Carlos Alberla-Lopez, Juan Ruiz-Alzola
Changes in tissue stiffness correlate with pathological phenomena that can aid the diagnosis of several diseases
such as breast and prostate cancer. Ultrasound elastography measures the elastic properties of soft tissues using
ultrasound signals.
The standard way to estimate the displacement field from which researchers obtain the strain in elastography
is the time-domain cross-correlation estimator (TDE). Optical flow (OF) methods have been also characterized
and their use keeps increasing.
We introduce in this paper the use of a Modified Demons Algorithm (MDA) to estimate the displacement
field and we compare it with OF. A least-squares strain estimator (LSE) is applied to estimate the strain from the
displacement. The input for the algorithm comes from the ultrasound scanner standard video output; therefore,
its clinical implementation is immediate.
To test the algorithm, a tissuemimicking phantom was modeled as a 10x10x5 cm region containing a centered
10mm cylindrical inclusion three times stiffer than the surrounding material, and its elastic behavior was simulated
using COMSOL Multiphysics 3.2 software. Synthetic pre- and post-compression (1.25%) B-mode images
were computer generated using FIELD II ultrasound simulator. Afterward, the algorithm was tested with a
commercial CIRS breast elastography phantom, applying a 2% freehand compression.
Axial displacement fields and strain figures are presented and in the case of the synthetic one compared
to the ground truth given by the FE software. Although other researchers have used registration methods for
elastography, as far as we know, they have not been used as stand alone but together with elastic modulus
reconstruction or FE which iteratively varies material properties to improve registration.
Elastography, an ultrasound modality based on the relation between tissue strain and its mechanical properties, has a strong potential in the diagnosis and prognosis of tumors. For instance, tissue affected by breast and prostate cancer undergoes a change in its elastic properties. These changes can be measured using ultrasound signals. The standard way to visualize the elastic properties of tissues in elastography is the representation of the axial strain. Other approaches investigate the information contained in shear strain elastograms, vorticity or the representation of the full strain tensor. In this paper, we propose to represent the elastic behaviour of tissues through the visualization of the Strain Index, related with the trace of the strain tensor. Based on the mathematical interpretation of the strain tensor, this novel parameter is equivalent to the sum of the eigenvalues of the strain tensor, and constitutes a measure of the total amount of strain of the soft tissue. In order to show the potential of this visualization approach, a tissue-mimicking phantom was modeled as a 10x10x5 cm region containing a centered 10mm cylindrical inclusion three times stiffer than the surrounding material, and its elastic behavior was simulated using finite elements software. Synthetic pre- and post-compression (1.25%) B-mode images were computer-generated with ultrasound simulator. Results show that the visualization of the tensor trace significantly improves the representation and detection of inclusions, and can help add insight in the detection of different types of tumors.
Ultrasound elastography measures the elastic properties of soft tissues using ultrasound signals. The elastic
problem can be analyzed with tensor signal processing. In this work, we propose a new interpretation of elastography
through the deformation tensor and its decomposition into both the strain and vorticity tensors. Vorticity
gives information about the rotation of the inclusions that might help in the discrimination between malign
and benign tumors without using biopsy. Although clinical validation is needed, synthetic experiments present
reliable results.
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