| 1. |
- Hosseinzadegan, Samar, 1987, et al.
(författare)
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Comparison of Two Forward Models For Electric Field of Microwave Imaging Systems
- 2017
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Ingår i: 2017 IEEE INTERNATIONAL SYMPOSIUM ON ANTENNAS AND PROPAGATION & USNC/URSI NATIONAL RADIO SCIENCE MEETING. - 1522-3965. - 9781538632840 ; 2017-January, s. 969-970
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Konferensbidrag (refereegranskat)abstract
- We propose an alternative numerical method, discrete dipole approximation (DDA), to model the two dimensional electric field of forward solution. Our observations show that discrete dipole approximation can be used as a fast and reliable numerical method on the forward solution of the microwave imaging systems. Two dimensional electric field of the microwave imaging systems has been modelled in finite element method with help of COMSOL Multiphysics as well. The numerical experiments obtained from COMSOL Multiphysics agree well with the discrete dipole approximation approach.
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| 2. |
- Meaney, Paul M, 1960, et al.
(författare)
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Conformal mesh and two-step tomographic imaging of the Supelec breast phantom
- 2017
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Ingår i: 2016 IEEE Conference on Antenna Measurements and Applications, CAMA 2016, Syracuse, United States, 23-27 October 2016.
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Konferensbidrag (refereegranskat)abstract
- The realistic breast phantom developed by the French team at Supelec provides an excellent opportunity to explore various measurement systems and associated algorithms. In this case there is a known ground truth for the geometry of the segmented regions for direct comparison of images with actual sizes, shapes and locations of the different features. It also allows for testing utilizing a range of dielectric materials for both the adipose and fibroglandular region which can be useful given the disparity of published property values. For this experiment, we are exploring our tomographic imaging algorithm with a log transformation in the context of restricting the imaging zone strictly to that space occupied by the phantom. In this case, the 2-dimensional perimeter of the breast was approximated by a simple ellipse which was extracted from the original image. All images were recovered without the assistance of a priori information and also included our 2-step imaging scheme. Simple parameter tests were performed to assess the limitations of the technique, especially when the imaging zone was not accurately determined. The final results were also analyzed by examination of histograms of the field residuals to assess whether the algorithm is robust and unbiased.
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| 3. |
- Meaney, Paul M, 1960, et al.
(författare)
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Electrical Characterization of Glycerin: Water Mixtures: Implications for Use as a Coupling Medium in Microwave Tomography
- 2017
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Ingår i: IEEE Transactions on Microwave Theory and Techniques. - 0018-9480 .- 1557-9670. ; 65:5, s. 1471-1478
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Tidskriftsartikel (refereegranskat)abstract
- We examine the broadband behavior of complex electrical properties of glycerin and water mixtures over the frequency range of 0.1-25.0 GHz, especially as they relate to using these liquids as coupling media for microwave tomographic imaging. Their combination is unique in that they are mutually miscible over the full range of concentrations, which allows them to be tailored to dielectric property matching for biological tissues. While the resultant mixture properties are partially driven by differences in the inherent low-frequency permittivity of each constituent, relaxation frequency shifts play a disproportionately larger role in increasing the permittivity dispersion while also dramatically increasing the effective conductivity over the frequency range of 1-3 GHz. For the full range of mixture ratios, the relaxation frequency shifts from 17.5 GHz for 0% glycerin to less than 0.1 GHz for 100% glycerin. Of particular interest is the fact that the conductivity stays above 1.0 S/m over the 1-3-GHz range for glycerin mixture ratios (70%-90% glycerin) we use for microwave breast tomography. The high level of attenuation is critical for suppressing unwanted multipath signals. This paper presents a full characterization of these liquids along with a discussion of their benefits and limitations in the context of microwave tomography.
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| 4. |
- Meaney, Paul M, 1960, et al.
(författare)
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Examination of the phase and log magnitude measurement projections and the implications for tomographic image reconstruction behavior
- 2017
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Ingår i: 2017 1st IEEE MTT-S International Microwave Bio Conference, IMBioC 2017. - 9781538617137
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Konferensbidrag (refereegranskat)abstract
- We examine the log magnitude and phase projections of simple circular objects in a 2D microwave tomography setting. Because of the inherent insight visible with these log transformed quantities, we can explore the forward and associated inverse scattering characteristics. For these situations, it is clear that the reconstructions for the cases where the target properties are higher than that of the background take more iterations and the convergence behavior is more uneven. Interestingly this corresponds to the situation where the composite pattern from the antenna/target combination produces a crudely focused beam with corresponding side nulls and lobes. We speculate that these features are somewhat confounding and ultimately prove more challenging for the reconstruction algorithm than for when the target properties are less than the background.
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| 5. |
- Meaney, Paul M, 1960, et al.
(författare)
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y Two-step inversion with a logarithmic transformation for microwave breast imaging
- 2017
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Ingår i: Medical Physics. - : Wiley. - 2473-4209 .- 0094-2405. ; 44:8, s. 4239-4251
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Tidskriftsartikel (refereegranskat)abstract
- Purpose: The authors have developed a new two-step microwave tomographic image reconstruction process specifically designed to incorporate logarithmic transformed microwave imaging algorithms as a means of significantly improving spatial resolution and target property recovery. Log transform eliminates the need for a priori information, but spatial filtering often integrated as part of the regularization required to stabilize image recovery, generally smooths image features and reduces object definition. The new implementation begins with this smoothed image as the first step, but then utilizes it as the starting estimate for a second step which continues the iterative process with a standard weighted Euclidean distance regularization. The penalty term of the latter restricts the new image to a multi-dimensional location close to the original but allows the algorithm to optimize the image without excessive smoothing. Methods: The overall approach is based on a Gauss-Newton iterative scheme which incorporates a log transformation as a way of making the reconstruction more linear. It has been shown to be robust and not require a priori information as a condition for convergence, but does produce somewhat smoothed images as a result of associated regularization. The new two-step process utilizes the previous technique to generate a smoothed initial estimate and then uses the same reconstruction process with a weighted Euclidean distance penalty term. A simple and repeatable method has been implemented to determine the weighting factor without significant computational burden. The reconstructions are assessed according to conventional parameter estimation metrics. Results: We apply the approach to phantom experiments using large, high contrast canonical shapes followed by a set of images recovered from an actual patient exam. The image improvements are substantial in regards to improved property recovery and feature delineation without inducing unwanted artifacts. Analysis of the residual vector after the reconstruction process further emphasizes that the minimization criterion is efficient with minimal biases. Conclusions: The outcome is a novel synergism of an established stable reconstruction algorithm with a conventional regularization technique. It maintains the ability to recover high quality microwave tomographic images without the bias of a priori information while substantially improving image quality. The results are confirmed on both phantom experiments and patient exams.
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| 6. |
- Rydholm, Tomas, 1991, et al.
(författare)
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A First Evaluation of the Realistic Supelec-Breast Phantom
- 2017
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Ingår i: IEEE Journal of Electromagnetics, RF and Microwaves in Medicine and Biology. - 2469-7249. ; 1:2, s. 59-65
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Tidskriftsartikel (refereegranskat)abstract
- A microwave tomographic system is used to evaluate the realistic breast phantom developed at the Supelec institute. The system utilizes 16 monopole antennas and a modern vector network analyzer (VNA) to measure the phantoms influence on the S-parameters. An iterative algorithm is then used to solve the inverse problem and reconstruct a 2-D plane transecting the phantom. The reconstructed images are compared to the ones recovered from a cylindrical phantom of equivalent phantom media. The results show that both phantoms are possible to reconstruct, although the interior of the Supelec phantom is more challenging.
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| 7. |
- Rydholm, Tomas, 1991, et al.
(författare)
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Microwave tomographic image improvement by fitting to a Cole-Cole relaxation model
- 2017
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Ingår i: 2017 11th European Conference on Antennas and Propagation, EUCAP 2017. - 9788890701870 ; , s. 682-684
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Konferensbidrag (refereegranskat)abstract
- We have reconstructed microwave tomographic images of the Supelec breast phantom using our imaging fixture in combination with a multi-channel vector network analyzer. During this study we were able to recover images without the support of a priori information over a broad frequency range - 1100-1900 MHz. We then fitted the spectral values at each pixel within the field of view to a Cole-Cole curve and extracted the coefficients at each location. While the individual images at each frequency provided reasonably representations of the target permittivity and conductivity distributions, the fibroglandular features were generally quite blurred with the surrounding adipose region. However, several of the Cole-Cole coefficient plots provided a higher level of resolution for the inclusions. While there was a noticeably high level of artifacts outside of the breast phantom perimeter, the internal structures are quite representative of the target. This is one of the first Cole-Cole image fittings using broadband measurement data on an actual phantom and sets the stage for higher specificity imaging.
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