Research

15 pages, 15355 KiB

Open AccessArticle

Comparing Radar-Based Breast Imaging Algorithm Performance with Realistic Patient-Specific Permittivity Estimation

by Declan O’Loughlin, Bárbara L. Oliveira, Martin Glavin, Edward Jones and Martin O’Halloran

J. Imaging 2019, 5(11), 87; https://doi.org/10.3390/jimaging5110087 - 19 Nov 2019

Cited by 9 | Viewed by 4639

Radar-based breast imaging has shown promise as an imaging modality for early-stage cancer detection, and clinical investigations of two commercial imaging systems are ongoing. Many imaging algorithms have been proposed, which seek to improve the quality of the reconstructed microwave image to enhance [...] Read more.

Radar-based breast imaging has shown promise as an imaging modality for early-stage cancer detection, and clinical investigations of two commercial imaging systems are ongoing. Many imaging algorithms have been proposed, which seek to improve the quality of the reconstructed microwave image to enhance the potential clinical decision. However, in many cases, the radar-based imaging algorithms have only been tested in limited numerical or experimental test cases or with simplifying assumptions such as using one estimate of permittivity for all patient test cases. In this work, the potential impact of patient-specific permittivity estimation on algorithm comparison is highlighted using representative experimental breast phantoms. In particular, the case studies presented help show that the permittivity estimate can impact the conclusions of the algorithm comparison. Overall, this work suggests that it is important that imaging algorithm comparisons use realistic test cases with and without breast abnormalities and with reconstruction permittivity estimation. Full article

(This article belongs to the Special Issue Microwave Imaging and Electromagnetic Inverse Scattering Problems)

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14 pages, 529 KiB

Open AccessArticle

A Finite-Difference Approach for Plasma Microwave Imaging Profilometry

by Loreto Di Donato, David Mascali, Andrea F. Morabito and Gino Sorbello

J. Imaging 2019, 5(8), 70; https://doi.org/10.3390/jimaging5080070 - 12 Aug 2019

Cited by 6 | Viewed by 4243

Abstract

Plasma diagnostics is a topic of great interest in the physics and engineering community because the monitoring of plasma parameters plays a fundamental role in the development and optimization of plasma reactors. Towards this aim, microwave diagnostics, such as reflectometric, interferometric, and polarimetric [...] Read more.

Plasma diagnostics is a topic of great interest in the physics and engineering community because the monitoring of plasma parameters plays a fundamental role in the development and optimization of plasma reactors. Towards this aim, microwave diagnostics, such as reflectometric, interferometric, and polarimetric techniques, can represent effective means. Besides the above, microwave imaging profilometry (MIP) may allow the obtaining of tomographic, i.e., volumetric, information of plasma that could overcome some intrinsic limitations of the standard non-invasive diagnostic approaches. However, pursuing MIP is not an easy task due to plasma’s electromagnetic features, which strongly depend on the working frequency, angle of incidence, polarization, etc., as well as on the need for making diagnostics in both large (meter-sized) and small (centimeter-sized) reactors. Furthermore, these latter represent extremely harsh environments, wherein different systems and equipment need to coexist to guarantee their functionality. Specifically, MIP entails solution of an inverse scattering problem, which is non-linear and ill-posed, and, in addition, in the one-dimensional case, is also severely limited in terms of achievable reconstruction accuracy and resolution. In this contribution, we address microwave inverse profiling of plasma assuming a high-frequency probing regime when magnetically confined plasma can be approximated as both an isotropic and weak penetrable medium. To this aim, we adopt a finite-difference frequency-domain (FDFD) formulation which allows dealing with non-homogeneous backgrounds introduced by unavoidable presence of plasma reactors. Full article

(This article belongs to the Special Issue Microwave Imaging and Electromagnetic Inverse Scattering Problems)

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13 pages, 943 KiB

Open AccessArticle

Image-Based RCS Estimation from Near-Field Data

by Tushar Rajvanshi, Maria Antonia Maisto, Angela Dell’Aversano and Raffaele Solimene

J. Imaging 2019, 5(6), 61; https://doi.org/10.3390/jimaging5060061 - 17 Jun 2019

Cited by 1 | Viewed by 5834

Abstract

This paper deals with the problem of estimating the RCS from near-field data by image-based approaches. In particular, a rigorous focusing procedure based on a weighted adjoint scheme, which is also applicable to an arbitrary measurement curve, is developed. The developed formalism allows [...] Read more.

This paper deals with the problem of estimating the RCS from near-field data by image-based approaches. In particular, a rigorous focusing procedure based on a weighted adjoint scheme, which is also applicable to an arbitrary measurement curve, is developed. The developed formalism allows us to address the important question concerning the need to employ a multi-frequency configuration to estimate the RCS. Accordingly, it is shown that if RCS is required at a given frequency, then the target image obtained solely at such a frequency can be exploited provided that the spatial truncation arising from the size of the investigated area is properly taken into account. Full article

(This article belongs to the Special Issue Microwave Imaging and Electromagnetic Inverse Scattering Problems)

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22 pages, 892 KiB

Open AccessArticle

Novel Stopping Criteria for Optimization-Based Microwave Breast Imaging Algorithms

by Cameron Kaye, Ian Jeffrey and Joe LoVetri

J. Imaging 2019, 5(5), 55; https://doi.org/10.3390/jimaging5050055 - 22 May 2019

Cited by 5 | Viewed by 4697

Abstract

A discontinuous Galerkin formulation of the Contrast Source Inversion algorithm (DGM-CSI) for microwave breast imaging employing a frequency-cycling reconstruction technique has been modified here to include a set of automated stopping criteria that determine a suitable time to shift imaging frequencies and to [...] Read more.

A discontinuous Galerkin formulation of the Contrast Source Inversion algorithm (DGM-CSI) for microwave breast imaging employing a frequency-cycling reconstruction technique has been modified here to include a set of automated stopping criteria that determine a suitable time to shift imaging frequencies and to globally terminate the reconstruction. Recent studies have explored the use of tissue-dependent geometrical mapping of the well-reconstructed real part to its imaginary part as initial guesses during consecutive frequency hops. This practice was shown to improve resulting 2D images of the dielectric properties of synthetic breast models, but a fixed number of iterations was used to halt DGM-CSI inversions arbitrarily. Herein, a new set of stopping conditions is introduced based on an intelligent statistical analysis of a window of past iterations of data error using the two-sample Kolmogorov-Smirnov (K-S) test. This non-parametric goodness-of-fit test establishes a pattern in the data error distribution, indicating an appropriate time to shift frequencies, or terminate the algorithm. The proposed stopping criteria are shown to improve the efficiency of DGM-CSI while yielding images of equivalent quality to assigning an often liberally overestimated number of iterations per reconstruction. Full article

(This article belongs to the Special Issue Microwave Imaging and Electromagnetic Inverse Scattering Problems)

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11 pages, 420 KiB

Open AccessArticle

A Minimum Rank Approach for Reduction of Environmental Noise in Near-Field Array Antenna Diagnosis

by Marco Donald Migliore, Fulvio Schettino, Daniele Pinchera, Mario Lucido and Gaetano Panariello

J. Imaging 2019, 5(5), 51; https://doi.org/10.3390/jimaging5050051 - 02 May 2019

Cited by 1 | Viewed by 4429

Abstract

A method to filter out the contribution of interference sources in array diagnosis is proposed. The interference-affected near field measured on a surface is treated as a (complex-data) image. This allows to use some modern image processing algorithms. In particular, two strategies widely [...] Read more.

A method to filter out the contribution of interference sources in array diagnosis is proposed. The interference-affected near field measured on a surface is treated as a (complex-data) image. This allows to use some modern image processing algorithms. In particular, two strategies widely used in image processing are applied. The first one is the reduction of the amount of information by acquiring only the innovation part of an image, as currently happens in video processing. More specifically, a differential measurement technique is used to formulate the estimation of the array excitations as a sparse recovery problem. The second technique has been recently proposed in video denoising, where the image is split into a low-rank and high-rank part. In particular, in this paper the interference field is filtered out using sparsity as discriminant adopting a mixed minimum

ℓ_{1}

norm and trace norm minimization algorithm. The methodology can be applied to both near and far field measurement ranges. It could be an alternative to the systematic use of anechoic chambers for antenna array testing. Full article

(This article belongs to the Special Issue Microwave Imaging and Electromagnetic Inverse Scattering Problems)

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14 pages, 5269 KiB

Open AccessArticle

Qualitative Methods for the Inverse Obstacle Problem: A Comparison on Experimental Data

by Martina T. Bevacqua and Roberta Palmeri

J. Imaging 2019, 5(4), 47; https://doi.org/10.3390/jimaging5040047 - 10 Apr 2019

Cited by 14 | Viewed by 4675

Abstract

Qualitative methods are widely used for the solution of inverse obstacle problems. They allow one to retrieve the morphological properties of the unknown targets from the scattered field by avoiding dealing with the problem in its full non-linearity and considering a simplified mathematical [...] Read more.

Qualitative methods are widely used for the solution of inverse obstacle problems. They allow one to retrieve the morphological properties of the unknown targets from the scattered field by avoiding dealing with the problem in its full non-linearity and considering a simplified mathematical model with a lower computational burden. Very many qualitative approaches have been proposed in the literature. In this paper, a comparison is performed in terms of performance amongst three different qualitative methods, i.e., the linear sampling method, the orthogonality sampling method, and a recently introduced method based on joint sparsity and equivalence principles. In particular, the analysis is focused on the inversion of experimental data and considers a wide range of (distinct) working frequencies and different kinds of scattering experiments. Full article

(This article belongs to the Special Issue Microwave Imaging and Electromagnetic Inverse Scattering Problems)

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17 pages, 1466 KiB

Open AccessArticle

Contraction Integral Equation for Three-Dimensional Electromagnetic Inverse Scattering Problems

by Yu Zhong and Kuiwen Xu

J. Imaging 2019, 5(2), 27; https://doi.org/10.3390/jimaging5020027 - 08 Feb 2019

Cited by 11 | Viewed by 5638

Abstract

Inverse scattering problems (ISPs) stand at the center of many important imaging applications, such as geophysical explorations, industrial non-destructive testing, bio-medical imaging, etc. Recently, a new type of contraction integral equation for inversion (CIE-I) has been proposed to tackle the two-dimensional electromagnetic ISPs, [...] Read more.

Inverse scattering problems (ISPs) stand at the center of many important imaging applications, such as geophysical explorations, industrial non-destructive testing, bio-medical imaging, etc. Recently, a new type of contraction integral equation for inversion (CIE-I) has been proposed to tackle the two-dimensional electromagnetic ISPs, in which the usually employed Lippmann–Schwinger integral equation (LSIE) is transformed into a new form with a modified medium contrast via a contraction mapping. With the CIE-I, the multiple scattering effects, i.e., the physical reason for the nonlinearity in the ISPs, is substantially suppressed in estimating the modified contrast, without compromising physical modeling. In this paper, we firstly propose to implement this new CIE-I for the three-dimensional ISPs. With the help of the FFT type twofold subspace-based optimization method (TSOM), when handling the highly nonlinear problems with strong scatterers, those with higher contrast and/or larger dimensions (in terms of wavelengths), the performance of the inversions with CIE-I is much better than the ones with the LSIE, wherein inversions usually converge to local minima that may be far away from the solution. In addition, when handling the moderate scatterers (those the LSIE modeling can still handle), the convergence speed of the proposed method with CIE-I is much faster than the one with the LSIE. Secondly, we propose to relax the contraction mapping condition, i.e., different contraction mappings are used in updating contrast sources and contrast, and we find that the convergence can be further accelerated. Several numerical tests illustrate the aforementioned interests. Full article

(This article belongs to the Special Issue Microwave Imaging and Electromagnetic Inverse Scattering Problems)

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19 pages, 2340 KiB

Open AccessArticle

Developments in Electrical-Property Tomography Based on the Contrast-Source Inversion Method

by Reijer Leijsen, Patrick Fuchs, Wyger Brink, Andrew Webb and Rob Remis

J. Imaging 2019, 5(2), 25; https://doi.org/10.3390/jimaging5020025 - 01 Feb 2019

Cited by 8 | Viewed by 5847

Abstract

The main objective of electrical-property tomography (EPT) is to retrieve dielectric tissue parameters from

{\hat{B}}_{1}^{+}

data as measured by a magnetic-resonance (MR) scanner. This is a so-called hybrid inverse problem in which data are defined inside the reconstruction domain of [...] Read more.

The main objective of electrical-property tomography (EPT) is to retrieve dielectric tissue parameters from

{\hat{B}}_{1}^{+}

data as measured by a magnetic-resonance (MR) scanner. This is a so-called hybrid inverse problem in which data are defined inside the reconstruction domain of interest. In this paper, we discuss recent and new developments in EPT based on the contrast-source inversion (CSI) method. After a short review of the basics of this method, two- and three-dimensional implementations of CSI–EPT are presented along with a very efficient variant of 2D CSI–EPT called first-order induced current EPT (foIC-EPT). Practical implementation issues that arise when applying the method to measured data are addressed as well, and the limitations of a two-dimensional approach are extensively discussed. Tissue-parameter reconstructions of an anatomically correct male head model illustrate the performance of two- and three-dimensional CSI–EPT. We show that 2D implementation only produces reliable reconstructions under very special circumstances, while accurate reconstructions can be obtained with 3D CSI–EPT. Full article

(This article belongs to the Special Issue Microwave Imaging and Electromagnetic Inverse Scattering Problems)

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24 pages, 1336 KiB

Open AccessArticle

Full-Vectorial 3D Microwave Imaging of Sparse Scatterers through a Multi-Task Bayesian Compressive Sensing Approach

by Marco Salucci, Lorenzo Poli and Giacomo Oliveri

J. Imaging 2019, 5(1), 19; https://doi.org/10.3390/jimaging5010019 - 15 Jan 2019

Cited by 4 | Viewed by 5618

Abstract

In this paper, the full-vectorial three-dimensional (3D) microwave imaging (MI) of sparse scatterers is dealt with. Towards this end, the inverse scattering (IS) problem is formulated within the contrast source inversion (CSI) framework and it [...] Read more.

In this paper, the full-vectorial three-dimensional (3D) microwave imaging (MI) of sparse scatterers is dealt with. Towards this end, the inverse scattering (IS) problem is formulated within the contrast source inversion (CSI) framework and it is aimed at retrieving the sparsest and most probable distribution of the contrast source within the imaged volume. A customized multi-task Bayesian compressive sensing (MT-BCS) method is used to yield regularized solutions of the 3D-IS problem with a remarkable computational efficiency. Selected numerical results on representative benchmarks are presented and discussed to assess the effectiveness and the reliability of the proposed MT-BCS strategy in comparison with other competitive state-of-the-art approaches, as well. Full article

(This article belongs to the Special Issue Microwave Imaging and Electromagnetic Inverse Scattering Problems)

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9 pages, 2539 KiB

Open AccessArticle

A Tomograph Prototype for Quantitative Microwave Imaging: Preliminary Experimental Results

by Alessandro Fedeli, Manuela Maffongelli, Ricardo Monleone, Claudio Pagnamenta, Matteo Pastorino, Samuel Poretti, Andrea Randazzo and Andrea Salvadè

J. Imaging 2018, 4(12), 139; https://doi.org/10.3390/jimaging4120139 - 26 Nov 2018

Cited by 15 | Viewed by 5758

Abstract

A new prototype of a tomographic system for microwave imaging is presented in this paper. The target being tested is surrounded by an ad-hoc 3D-printed structure, which supports sixteen custom antenna elements. The transmission measurements between each pair of antennas are acquired through [...] Read more.

A new prototype of a tomographic system for microwave imaging is presented in this paper. The target being tested is surrounded by an ad-hoc 3D-printed structure, which supports sixteen custom antenna elements. The transmission measurements between each pair of antennas are acquired through a vector network analyzer connected to a modular switching matrix. The collected data are inverted by a hybrid nonlinear procedure combining qualitative and quantitative reconstruction algorithms. Preliminary experimental results, showing the capabilities of the developed system, are reported. Full article

(This article belongs to the Special Issue Microwave Imaging and Electromagnetic Inverse Scattering Problems)

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