SwePub - search: WFRF:(Meaney Paul M 1960)

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1.	Golnabi, Amir H., et al. (author) 3-D Microwave Tomography Using the Soft Prior Regularization Technique: Evaluation in Anatomically Realistic MRI-Derived Numerical Breast Phantoms 2019 In: IEEE Transactions on Biomedical Engineering. - 0018-9294 .- 1558-2531. ; 66:9, s. 2566-2575 Journal article (peer-reviewed)abstract Objective: Fusion of magnetic resonance imaging (MRI) breast images with microwave tomography is accomplished through a soft prior technique, which incorporates spatial information (from MRI), i. e., accurate boundary location of different regions of interest, into the regularization process of the microwave image reconstruction algorithm. Methods: Numerical experiments were completed on a set of three-dimensional (3-D) breast geometries derived from MR breast data with different parenchymal densities, as well as a simulated tumor to evaluate the performance over a range of breast shapes, sizes, and property distributions. Results: When the soft prior regularization technique was applied, both permittivity and conductivity relative root mean square error values decreased by more than 87% across all breast densities, except in two cases where the error decrease was only 55% and 78%. In addition, the incorporation of structural priors increased contrast between tumor and fibroglandular tissue by 59% in permittivity and 192% in conductivity. Conclusion: This study confirmed that the soft prior algorithm is robust in 3-D and can function successfully across a range of complex geometries and tissue property distributions. Significance: This study demonstrates that our microwave tomography is capable of recovering accurate tissue property distributions when spatial information from MRI is incorporated through soft prior regularization.
2.	Hosseinzadegan, Samar, 1987, et al. (author) A discrete dipole approximation solver based on the COCG-FFT algorithm and its application to microwave breast imaging 2019 In: International Journal of Antennas and Propagation. - : Hindawi Limited. - 1687-5869 .- 1687-5877. ; 2019 Journal article (peer-reviewed)abstract We introduce the discrete dipole approximation (DDA) for efficiently calculating the two-dimensional electric field distribution for our microwave tomographic breast imaging system. For iterative inverse problems such as microwave tomography, the forward field computation is the time limiting step. In this paper, the two-dimensional algorithm is derived and formulated such that the iterative conjugate orthogonal conjugate gradient (COCG) method can be used for efficiently solving the forward problem. We have also optimized the matrix-vector multiplication step by formulating the problem such that the nondiagonal portion of the matrix used to compute the dipole moments is block-Toeplitz. The computation costs for multiplying the block matrices times a vector can be dramatically accelerated by expanding each Toeplitz matrix to a circulant matrix for which the convolution theorem is applied for fast computation utilizing the fast Fourier transform (FFT). The results demonstrate that this formulation is accurate and efficient. In this work, the computation times for the direct solvers, the iterative solver (COCG), and the iterative solver using the fast Fourier transform (COCG-FFT) are compared with the best performance achieved using the iterative solver (COCG-FFT) in C++. Utilizing this formulation provides a computationally efficient building block for developing a low cost and fast breast imaging system to serve under-resourced populations.
3.	Hosseinzadegan, Samar, 1987, et al. (author) Application of the discrete dipole approximation in microwave breast imaging 2019 In: Proceedings of the 2019 21st International Conference on Electromagnetics in Advanced Applications, ICEAA 2019. ; , s. 0868-0868 Conference paper (peer-reviewed)abstract In this work, we propose the two-dimensional discrete dipole approximation (2D DDA) to calculate the electric field distributions in the microwave imaging system. The motive is to develop a significantly fast reconstruction algorithm. To accomplish this, the 2D DDA on a uniform grid in the forward model zone is used, which enables computational times be significantly reduced compared to common algorithms.
4.	Hosseinzadegan, Samar, 1987, et al. (author) Application of two-dimensional discrete dipole approximation in simulating electric field of a microwave breast imaging system 2019 In: IEEE Journal of Electromagnetics, RF and Microwaves in Medicine and Biology. - 2469-7249. ; 3:2, s. 80-87 Journal article (peer-reviewed)abstract © 2016 IEEE. The 2-D electric field distribution of the microwave imaging system is numerically simulated for a simplified breast tumour model. The proposed two-dimensional discrete dipole approximation (DDA) has the potential to improve computational speed compared to other numerical methods while retaining comparable accuracy. We have modeled the field distributions in COMSOL Multiphysics as baseline results to benchmark the DDA simulations. We have also investigated the adequate sampling size and the effect of inclusion size and property contrast on solution accuracy. In this way, we can utilize the 2-D DDA as an alternative, fast, and reliable forward solver for microwave tomography. From a mathematical perspective, the derivation of the 2-D DDA and its application to microwave imaging is new and not previously implemented. The simulation results and the measurements show that the 2-D DDA is a well-grounded forward solver for the specified microwave breast imaging system.
5.	Hosseinzadegan, Samar, 1987, et al. (author) Comparison of Two Forward Models For Electric Field of Microwave Imaging Systems 2017 In: 2017 IEEE INTERNATIONAL SYMPOSIUM ON ANTENNAS AND PROPAGATION & USNC/URSI NATIONAL RADIO SCIENCE MEETING. - 1522-3965. - 9781538632840 ; , s. 969-970 Conference paper (peer-reviewed)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.
6.	Hosseinzadegan, Samar, 1987, et al. (author) Discrete Dipole Approximation-Based Microwave Tomography for Fast Breast Cancer Imaging 2021 In: IEEE Transactions on Microwave Theory and Techniques. - 0018-9480 .- 1557-9670. ; 69:5, s. 2741-2752 Journal article (peer-reviewed)abstract This article describes a fast microwave tomography reconstruction algorithm based on the 2-D discrete dipole approximation (DDA). Synthetic data from a finite-element-based solver and experimental data from a microwave imaging system are used to reconstruct images and to validate the algorithm. The microwave measurement system consists of 16 monopole antennas immersed in a tank filled with lossy coupling liquid and a vector network analyzer. The low-profile antennas and lossy nature of the system make the DDA an ideal forward solver in image reconstructions. The results show that the algorithm can readily reconstruct a 2-D plane of a cylindrical phantom. The proposed forward solver combined with the nodal adjoint method for computing the Jacobian matrix enables the algorithm to reconstruct an image within 6 s. This implementation provides significant time savings and reduced memory requirements and is a dramatic improvement over previous implementations.
7.	Hosseinzadegan, Samar, 1987, et al. (author) Expansion of the nodal-adjoint method for simple and efficient computation of the 2d tomographic imaging jacobian matrix 2021 In: Sensors. - : MDPI AG. - 1424-8220. ; 21:3, s. 1-16 Journal article (other academic/artistic)abstract This paper focuses on the construction of the Jacobian matrix required in tomographic reconstruction algorithms. In microwave tomography, computing the forward solutions during the iterative reconstruction process impacts the accuracy and computational efficiency. Towards this end, we have applied the discrete dipole approximation for the forward solutions with significant time savings. However, while we have discovered that the imaging problem configuration can dramatically impact the computation time required for the forward solver, it can be equally beneficial in constructing the Jacobian matrix calculated in iterative image reconstruction algorithms. Key to this implementation, we propose to use the same simulation grid for both the forward and imaging domain discretizations for the discrete dipole approximation solutions and report in detail the theoretical aspects for this localization. In this way, the computational cost of the nodal adjoint method decreases by several orders of magnitude. Our investigations show that this expansion is a significant enhancement compared to previous implementations and results in a rapid calculation of the Jacobian matrix with a high level of accuracy. The discrete dipole approximation and the newly efficient Jacobian matrices are effectively implemented to produce quantitative images of the simplified breast phantom from the microwave imaging system.
8.	Hosseinzadegan, Samar, 1987, et al. (author) Fast Jacobian Matrix Formulation for Microwave Tomography Applications 2021 In: 15th European Conference on Antennas and Propagation, EuCAP 2021. Conference paper (peer-reviewed)abstract We have developed a new technique for computing the Jacobian matrix for microwave tomography systems which is orders of magnitude faster than conventional approaches. It exploits concepts from the nodal adjoint method and previous observations that rows of the matrix can be plotted over the imaging domain to produce sensitivity maps associated with specific transmit/receive antenna pairs. It also requires that the forward solutions and parameter reconstruction distributions be represented on the same grid or mesh. In this way, it computes full rows of the matrix simultaneously via a simple vector-vector multiplication of the forward solutions associated with sources broadcasting from both the designated transmit and receive antennas times a scalar constant. The time savings is substantial and is viable for both 2D and 3D applications.
9.	Hosseinzadegan, Samar, 1987, et al. (author) Integrating the discrete dipole approximation forward solver with a microwave tomography algorithm 2018 In: 2018 IEEE ANTENNAS AND PROPAGATION SOCIETY INTERNATIONAL SYMPOSIUM ON ANTENNAS AND PROPAGATION & USNC/URSI NATIONAL RADIO SCIENCE MEETING. - 1522-3965. - 9781538671023 - 9781538671023 ; , s. 2295-2296 Conference paper (peer-reviewed)abstract The discrete dipole approximation (DDA) has been suggested as a viable alternative method for computing the forward solutions during the iterative reconstruction process used in microwave tomography. While efficient algorithms such as finite difference time domain and finite elements have been successfully used by multiple groups, the forward solution time remains the time-limiting step. The DDA has been shown to be accurate and efficient as a forward solver. However, the configuration of the imaging scenario can have a significant impact on its efficiency. We examine two possible forward solution set-ups and describe the benefits with respect to implementing the DDA.
10.	Hosseinzadegan, Samar, 1987, et al. (author) On the electric field of microwave imaging systems using discrete dipole approximation 2018 In: 2018 IEEE Conference on Antenna Measurements and Applications, CAMA 2018. - 9781538657959 Conference paper (peer-reviewed)abstract The two dimensional electric field for our microwave imaging system consisting of 16 low profile monopole antennas is modelled via the discrete dipole approximation (DDA). We have used two dimensional electromagnetic waves in frequency domain in COMSOL Multiphysics to assess the level of reliability of the proposed two dimensional numerical solver, the 2-D DDA. Our observations show that the DDA is mainly dependent on the applied resolution on the imaging domain while physical properties in the media also contribute to the overall error.
11.	Hosseinzadegan, Samar, 1987, et al. (author) Optimization of a microwave tomography algorithm using the DDA as a fast forward solver 2019 In: 2019 IEEE International Symposium on Antennas and Propagation and USNC-URSI Radio Science Meeting, APSURSI 2019 - Proceedings. ; , s. 1683-1684 Conference paper (peer-reviewed)abstract © 2019 IEEE. The forward model directly impacts the computation time of an iterative image reconstruction algorithm for microwave tomography. Therefore, there is a need to decrease the computation time without sacrificing accuracy. To accomplish this, the discrete dipole approximation (DDA) is used to improve time efficiency. Although the DDA is an accurate and efficient forward solver, the optimization of its implementation can have a significant impact on its time efficiency. We propose a possible forward solution set-up to benefit in computation time efficiency. Optimizing the DDA implementation can decrease the computation time for a microwave tomography algorithm significantly, and thus produces images closer to real time.
12.	Meaney, Paul M, 1960, et al. (author) A 4-channel, vector network analyzer microwave imaging prototype based on software defined radio technology 2019 In: Review of Scientific Instruments. - : AIP Publishing. - 1089-7623 .- 0034-6748. ; 90:4 Journal article (peer-reviewed)abstract We have implemented a prototype 4-channel transmission-based, microwave measurement system built on innovative software defined radio (SDR) technology. The system utilizes the B210 USRP SDR developed by Ettus Research that operates over a 70 MHz-6 GHz bandwidth. While B210 units are capable of being synchronized with each other via coherent reference signals, they are somewhat unreliable in this configuration and the manufacturer recommends using N200 or N210 models instead. For our system, N-series SDRs were less suitable because they are not amenable to RF shielding required for the cross-channel isolation necessary for an integrated microwave imaging system. Consequently, we have configured an external reference that overcame these limitations in a compact and robust package. Our design exploits the rapidly evolving technology being developed for the telecommunications environment for test and measurement tasks with the higher performance specifications required in medical microwave imaging applications. In a larger channel configuration, the approach is expected to provide performance comparable to commercial vector network analyzers at a fraction of the cost and in a more compact footprint.
13.	Meaney, Paul M, 1960, et al. (author) A Transmission-Based Dielectric Property Probe for Clinical Applications 2018 In: Sensors. - : MDPI AG. - 1424-8220. ; 18:10 Journal article (peer-reviewed)abstract We have developed a transmission-based, open-ended coaxial dielectric probe that can be used in clinical situations and overcomes many of the limitations related to the typical reflection-based dielectric probes. The approach utilizes the low profile, open-ended coaxial cables enabling clinicians to still probe relatively compact spaces. The sensing depth can be extended to as large as 1.5 to 2 cm compared with the more typical range of 0.3 mm for conventional probes and is dramatically less affected by measurement technique variability including poor sample contact and cable bending. As a precursor to an actual clinical implementation, we study the technique in a range of homogeneous liquids with substantially varying dielectric properties. The initial results demonstrate good agreement between the transmission-based probe and commercial, reflection-based probes and pave the way for more substantial clinical implementation.
14.	Meaney, Paul M, 1960, et al. (author) Comments on "Investigation of Histology Region Dielectric Measurements of Heterogeneous Tissues" 2020 In: IEEE Transactions on Antennas and Propagation. - 0018-926X .- 1558-2221. ; 68:1, s. 615-616 Journal article (peer-reviewed)abstract In the article, "Investigation of histology region in dielectric measurements of heterogeneous tissues," by Porter and O'Halloran, the authors utilize a flexible phantom in a layered material dielectric property analysis to quantify the effective sensing volume of a coaxial dielectric probe. Ostensibly, this test has been used by others to characterize the region for which percent variation in the material composition in front of the probe corresponds to percent variation in the computed effective dielectric properties. By employing a compressible material, the authors fail to isolate features that are attributable solely to the probe, itself, and inadvertently incorporate confounding characteristics associated with the compressible nature of the material. The net effect is to exaggerate the probe's sensing volume, which undermines the conclusions drawn from the subsequent tissue dielectric property studies. © 2019 IEEE.
15.	Meaney, Paul M, 1960, et al. (author) Conformal mesh and two-step tomographic imaging of the Supelec breast phantom 2017 In: 2016 IEEE Conference on Antenna Measurements and Applications, CAMA 2016, Syracuse, United States, 23-27 October 2016. Conference paper (peer-reviewed)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.
16.	Meaney, Paul M, 1960, et al. (author) Electrical Characterization of Glycerin: Water Mixtures: Implications for Use as a Coupling Medium in Microwave Tomography 2017 In: IEEE Transactions on Microwave Theory and Techniques. - 0018-9480 .- 1557-9670. ; 65:5, s. 1471-1478 Journal article (peer-reviewed)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.
17.	Meaney, Paul M, 1960, et al. (author) Examination of the phase and log magnitude measurement projections and the implications for tomographic image reconstruction behavior 2017 In: 2017 1st IEEE MTT-S International Microwave Bio Conference, IMBioC 2017. - 9781538617137 Conference paper (peer-reviewed)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.
18.	Meaney, Paul M, 1960, et al. (author) Examination of the sensitivity matrix during the iterative reconstruction process for microwave tomography 2018 In: 2018 IEEE Conference on Antenna Measurements and Applications, CAMA 2018. Conference paper (peer-reviewed)abstract We have reconstructed microwave tomographic images utilizing a Gauss-Newton scheme with a log transformation. While the recovered images are quite good, we have analyzed the behavior of the associated Jacobian, or sensitivity, matrix with respect to how it evolves during the reconstruction process. We found that in general the highest sensitivities are along the periphery of the imaging zone confirming the fact that most algorithms operate best for features nearest the outside. Interestingly, our log transformed algorithm appears to evolve during the reconstruction process to increase its internal sensitivity once the major exterior ones have been resolved. These results provide useful insight into a key driver of the reconstruction process and provide useful tools for assessing different system design criteria.
19.	Meaney, Paul M, 1960, et al. (author) Quasi- Open-Ended Coaxial Dielectric Probe Array for Skin Burn Characterization 2019 In: 2019 13th European Conference On Antennas And Propagation (EUCAP). - : IEEE. - 9788890701887 Conference paper (peer-reviewed)abstract We have developed a planar probe for measuring dielectric properties. It exploits modern circuit board fabrication technologies that effectively construct a quasi-coaxial structure running perpendicular to the board. The feed line is a printed coplanar waveguide which comes in from the side on the top plane. The opening to the bottom behaves exactly like an open-ended coaxial probe. The initial results are comparable to the existing coaxial probes. The geometry of these probes allows them to be fabricated in an array utilizing standard, multi-layer circuit fabrication technology. These probe arrays may prove extremely useful in applications such as tumor margin detection for resected tissue, skin cancer screening and characterizing burns.
20.	Meaney, Paul M, 1960, et al. (author) Transmission-Based Dielectric Probes for Surgical Applications 2019 In: 13th European Conference on Antennas and Propagation, EuCAP 2019. Conference paper (peer-reviewed)abstract We have developed a new type of transmission-based dielectric probe that is idea for certain surgical applications - most notably spinal fusion surgery. It utilizes small-diameter open-ended coaxial cables, but exploits the fact that for the vertebrae surgery, the surgeon has access to both sides of the bone. While the space separation needs to be small (<2 cm), it is sufficiently large to get a signal across. The mathematics is dramatically simplified since it operates in the far field for which a number of simplifications can be employed. The penetration depth is effectively the full span between the two probes which is dramatically larger than that for open-ended coaxial reflection-based probes. Because it operates in the transmission mode, the effects from cable bending and such are minimal and subsequently lends itself to hand held operation which will be critical for a surgical setting.
21.	Meaney, Paul M, 1960, et al. (author) Two-step reconstruction process for microwave tomography without a priori information 2016 In: 2016 10th European Conference on Antennas and Propagation, EuCAP 2016. - 2164-3342. - 9788890701863 ; , s. Arti no 7481674- Conference paper (peer-reviewed)abstract While our log transform reconstruction algorithm provides significant advantages over competing algorithms because of its ability to converge to a unique, global solution without utilizing a priori information, the process still requires a modest amount of regularization which naturally tends to smooth the image and sometimes blur important features. We have integrated this overall technique with a novel 2-step reconstruction to produce significantly improved images with respect to feature definition without inducing unwanted artifacts. The critical challenge in this scenario is determining the regularization parameter for the Euclidean distance penalty term in the second step. In this case, because the algorithm is quite fast, the regularization term is computed using a simple linear search. Initial phantom experiment results indicate that targets as small as 5mm diameter are detectable and that the algorithm behaves as an efficient estimator according to standard parameter estimation metrics for a wide range of targets. Results also suggest that there are equally significant improvements in reconstructions from actual patient exams. © 2016 European Association of Antennas and Propagation.
22.	Meaney, Paul M, 1960, et al. (author) Visualization of the effects of multipath signals in complementary imaging and dielectric probing scenarios 2018 In: 2018 IEEE Conference on Antenna Measurements and Applications, CAMA 2018. - 9781538657959 Conference paper (peer-reviewed)abstract Distinguishing the effects of multipath signals from desired ones is often a challenging proposition. In this paper, we present two examples where multipath signals have impacted the desired signals. In each case, solutions were found to either further attenuate the unwanted signals to irrelevant levels or to understand their behavior as a means of developing ways to avoid such problems. These examples are reasonably representative of challenges encountered by all systems and are illustrative of the challenges they present.
23.	Meaney, Paul M, 1960, et al. (author) y Two-step inversion with a logarithmic transformation for microwave breast imaging 2017 In: Medical Physics. - : Wiley. - 2473-4209 .- 0094-2405. ; 44:8, s. 4239-4251 Journal article (peer-reviewed)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.
24.	Rubaek, Tonny, 1979, et al. (author) A Contrast Source Inversion Algorithm Formulated Using the Log-Phase Formulation 2011 In: International Journal of Antennas and Propagation. - : Hindawi Limited. - 1687-5869 .- 1687-5877. ; 2011 Journal article (peer-reviewed)abstract The contrast source inversion (CSI) algorithm was introduced for microwave imaging in 1997 and has since proven to be one of the most successful algorithms for nonlinear microwave tomography. In the CSI algorithm, the nonlinear integral equation, which must be solved to extract the constitutive electromagnetic parameters of the object under test from the microwave measurements, is represented by two linear equations, known as the data and the object equations. In this paper, the data equation in the CSI algorithm is reformulated using the so-called log-phase formulation. In this formulation, the measured data is represented by the change in the logarithm of the amplitude and the change in the unwrapped phase. This formulation has previously been applied for nonlinear tomography within the framework of a Gauss-Newton based algorithm for detection of breast cancer. Here, significant improvements have been observed compared to the more commonly used real-imaginary formulation. The modified CSI algorithm is tested on both simulated data and on a measurement of a breast. It is shown that for imaging setups with large differences in the measured signals, the new formulation of the data equation significantly improves the performance of the CSI algorithm.
25.	Rydholm, Tomas, 1991, et al. (author) A First Evaluation of the Realistic Supelec-Breast Phantom 2017 In: IEEE Journal of Electromagnetics, RF and Microwaves in Medicine and Biology. - 2469-7249. ; 1:2, s. 59-65 Journal article (peer-reviewed)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.
26.	Rydholm, Tomas, 1991, et al. (author) Comparing a time-domain and frequency-domain based algorithm in microwave tomography 2018 In: IET Conference Publications. - : Institution of Engineering and Technology. ; 2018:CP741 Conference paper (peer-reviewed)abstract A comparison of two different reconstruction algorithms developed for microwave tomographic imaging has been performed. One of the algorithm is an FDTD algorithm and the other one is an FEM-based one. Simulated S-parameters for a 16-antenna system are generated for a numerical phantom, which are then used to solve the inverse problem. It is shown that both algorithms could use the generated S-parameters to successfully reconstruct the studied phantoms.
27.	Rydholm, Tomas, 1991, et al. (author) Effects of the Plastic of the Realistic GeePS-L2S-Breast Phantom 2018 In: Diagnostics. - : MDPI AG. - 2075-4418. ; 8:3 Journal article (peer-reviewed)abstract A breast phantom developed at the Supelec Institute was interrogated to study its suitability for microwave tomography measurements. A microwave measurement system based on 16 monopole antennas and a vector network analyzer was used to study how the S-parameters are influenced by insertion of the phantom. The phantom is a 3D-printed structure consisting of plastic shells that can be filled with tissue mimicking liquids. The phantom was filled with different liquids and tested with the measurement system to determine whether the plastic has any effects on the recovered images or not. Measurements of the phantom when it is filled with the same liquid as the surrounding coupling medium are of particular interest. In this case, the phantom plastic has a substantial effects on the measurements which ultimately detracts from the desired images.
28.	Rydholm, Tomas, 1991, et al. (author) Microwave tomographic image improvement by fitting to a Cole-Cole relaxation model 2017 In: 2017 11th European Conference on Antennas and Propagation, EUCAP 2017. - 9788890701870 ; , s. 682-684 Conference paper (peer-reviewed)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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