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20 pages, 3345 KiB

Open AccessArticle

Dielectric Characterization of Healthy Human Teeth from 0.5 to 18 GHz with an Open-Ended Coaxial Probe

by Mariya Berezhanska, Daniela M. Godinho, Paulo Maló and Raquel C. Conceição

Sensors 2023, 23(3), 1617; https://doi.org/10.3390/s23031617 - 2 Feb 2023

Cited by 3 | Viewed by 1951

Abstract

Dental caries is a major oral health issue which compromises oral health, as it is the main cause of oral pain and tooth loss. Early caries detection is essential for effective clinical intervention. However, methods commonly employed for its diagnosis often fail to [...] Read more.

Dental caries is a major oral health issue which compromises oral health, as it is the main cause of oral pain and tooth loss. Early caries detection is essential for effective clinical intervention. However, methods commonly employed for its diagnosis often fail to detect early caries lesions, which motivates the research for more effective diagnostic solutions. In this work, the relative permittivity of healthy permanent teeth, in caries-prone areas, was studied between 0.5 and 18 GHz. The reliability of such measurements is an important first step to, ultimately, evaluate the feasibility of a microwave device for caries detection. The open-ended coaxial probe technique was employed. Its performance showed to be compromised by the poor probe-tooth contact. We proposed a method based on applying coupling media to reduce this limitation. A decrease in the measured relative permittivity variability was observed when the space between the probe tip and tooth surface was filled by coupling media instead of air. The influence of the experimental conditions in the measurement result was found to be less than 5%. Measurements conducted in ex vivo teeth showed that the relative permittivity of the dental crown and root ranges between 10.0–11.0 and 8.0–9.5, respectively. Full article

(This article belongs to the Special Issue Advances in Medical Microwave Imaging and Signal Processing, and Hyperthermic Technologies for Healthcare)

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18 pages, 1842 KiB

Open AccessArticle

A Novel Discretization Procedure in the CSI-FEM Algorithm for Brain Stroke Microwave Imaging

by Valeria Mariano, Jorge A. Tobon Vasquez and Francesca Vipiana

Sensors 2023, 23(1), 11; https://doi.org/10.3390/s23010011 - 20 Dec 2022

Cited by 6 | Viewed by 1622

Abstract

In this work, the contrast source inversion method is combined with a finite element method to solve microwave imaging problems. The paper’s major contribution is the development of a novel contrast source variable discretization that leads to simplify the algorithm implementation and, at [...] Read more.

In this work, the contrast source inversion method is combined with a finite element method to solve microwave imaging problems. The paper’s major contribution is the development of a novel contrast source variable discretization that leads to simplify the algorithm implementation and, at the same time, to improve the accuracy of the discretized quantities. Moreover, the imaging problem is recreated in a synthetic environment, where the antennas, and their corresponding coaxial port, are modeled. The implemented algorithm is applied to reconstruct the tissues’ dielectric properties inside the head for brain stroke microwave imaging. The proposed implementation is compared with the standard one to evaluate the impact of the variables’ discretization on the algorithm’s accuracy. Furthermore, the paper shows the obtained performances with the proposed and the standard implementations of the contrast source inversion method in the same realistic 3D scenario. The exploited numerical example shows that the proposed discretization can reach a better focus on the stroke region in comparison with the standard one. However, the variation is within a limited range of permittivity values, which is reflected in similar averages. Full article

(This article belongs to the Special Issue Advances in Medical Microwave Imaging and Signal Processing, and Hyperthermic Technologies for Healthcare)

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12 pages, 9043 KiB

Open AccessArticle

The Effect of Freezing and Thawing on Complex Permittivity of Bovine Tissues

by Anđela Matković and Antonio Šarolić

Sensors 2022, 22(24), 9806; https://doi.org/10.3390/s22249806 - 14 Dec 2022

Cited by 1 | Viewed by 1753

Abstract

The aim of this study was to investigate how the freezing and thawing of biological tissues affect their complex permittivity in the microwave frequency range from 0.5 MHz to 18 GHz. We measured the complex permittivity of ex vivo bovine tissues, including brain [...] Read more.

The aim of this study was to investigate how the freezing and thawing of biological tissues affect their complex permittivity in the microwave frequency range from 0.5 MHz to 18 GHz. We measured the complex permittivity of ex vivo bovine tissues, including brain white and grey matter, liver, and muscle, using an open-ended coaxial probe. Bovine tissues were chosen for their availability and similarity to human tissue permittivity. The samples were measured at 25 °C, before they were frozen either in a commercial freezer below −18 °C or in liquid nitrogen, nominally at −196 °C. The measured permittivity before freezing was compared to the permittivity measured after freezing and thawing the tissues back to 25 °C. Statistical analysis of the results showed a statistically significant change in permittivity after freezing and thawing by both methods for all the measured tissues, at least in some parts of the measured frequency range. The largest difference was observed for the white matter, while the liver had the smallest percent change. Full article

(This article belongs to the Special Issue Advances in Medical Microwave Imaging and Signal Processing, and Hyperthermic Technologies for Healthcare)

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12 pages, 3989 KiB

Open AccessArticle

Impact of Skin on Microwave Tomography in the Lossy Coupling Medium

by Paul Meaney, Shireen Geimer, Amir Golnabi and Keith Paulsen

Sensors 2022, 22(19), 7353; https://doi.org/10.3390/s22197353 - 28 Sep 2022

Cited by 3 | Viewed by 1359

Abstract

In microwave imaging, the effects of skin on recovering property distributions of tissue underneath the surface may be significant because it has high dielectric contrast with subcutaneous fat, which inevitably causes significant signal reflections. While the thickness of skin, especially relative to the [...] Read more.

In microwave imaging, the effects of skin on recovering property distributions of tissue underneath the surface may be significant because it has high dielectric contrast with subcutaneous fat, which inevitably causes significant signal reflections. While the thickness of skin, especially relative to the wavelengths in use, would presumably have minor effects, it can introduce practical difficulties, for instance, in reflection-based imaging techniques, where the impact of the skin is large—often as high as two orders of magnitude greater than that of signals from underlying tumors in the breast imaging setting. However, in tomography cases utilizing transmission-based measurement data and lossy coupling materials, the situation is considerably different. Accurately implementing a skin layer for numerical modeling purposes is challenging because of the need to discretize the size and shape of the skin without increasing computational overhead substantially. In this paper, we assess the effects of the skin on field solutions in a realistic 3D model of a human breast. We demonstrate that the small changes in transmission field values introduced by including the skin cause minor differences in reconstructed images. Full article

(This article belongs to the Special Issue Advances in Medical Microwave Imaging and Signal Processing, and Hyperthermic Technologies for Healthcare)

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15 pages, 23769 KiB

Open AccessArticle

Generation of Prior Information in a Dual-Mode Microwave-Ultrasound Breast Imaging System

by Hannah Fogel, Max Hughson, Mohammad Asefi, Ian Jeffrey and Joe LoVetri

Sensors 2022, 22(18), 7087; https://doi.org/10.3390/s22187087 - 19 Sep 2022

Cited by 4 | Viewed by 1939

Abstract

A new breast imaging system capable of obtaining ultrasound and microwave scattered-field measurements with minimal or no movement of the breast between measurements has recently been reported. In this work, we describe the methodology that has been developed to generate prior information about [...] Read more.

A new breast imaging system capable of obtaining ultrasound and microwave scattered-field measurements with minimal or no movement of the breast between measurements has recently been reported. In this work, we describe the methodology that has been developed to generate prior information about the internal structures of the breast based on ultrasound data measured with the dual-mode system. This prior information, estimating both the geometry and complex-valued permittivity of tissues within the breast, is incorporated into the microwave inversion algorithm as a means of enhancing image quality. Several techniques to map reconstructed ultrasound speed to complex-valued relative permittivity are investigated. Quantitative images of two simplified dual-mode breast phantoms obtained using experimental data and the various forms of prior information are presented. Though preliminary, the results presented herein provide an understanding of the impacts of different forms of prior information on dual-mode reconstructions of the breast and can be used to inform future work on the subject. Full article

(This article belongs to the Special Issue Advances in Medical Microwave Imaging and Signal Processing, and Hyperthermic Technologies for Healthcare)

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15 pages, 1654 KiB

Open AccessArticle

Antenna Excitation Optimization with Deep Learning for Microwave Breast Cancer Hyperthermia

by Gulsah Yildiz, Halimcan Yasar, Ibrahim Enes Uslu, Yusuf Demirel, Mehmet Nuri Akinci, Tuba Yilmaz and Ibrahim Akduman

Sensors 2022, 22(17), 6343; https://doi.org/10.3390/s22176343 - 23 Aug 2022

Cited by 13 | Viewed by 3525

Abstract

Microwave hyperthermia (MH) requires the effective calibration of antenna excitations for the selective focusing of the microwave energy on the target region, with a nominal effect on the surrounding tissue. To this end, many different antenna calibration methods, such as optimization techniques and [...] Read more.

Microwave hyperthermia (MH) requires the effective calibration of antenna excitations for the selective focusing of the microwave energy on the target region, with a nominal effect on the surrounding tissue. To this end, many different antenna calibration methods, such as optimization techniques and look-up tables, have been proposed in the literature. These optimization procedures, however, do not consider the whole nature of the electric field, which is a complex vector field; instead, it is simplified to a real and scalar field component. Furthermore, most of the approaches in the literature are system-specific, limiting the applicability of the proposed methods to specific configurations. In this paper, we propose an antenna excitation optimization scheme applicable to a variety of configurations and present the results of a convolutional neural network (CNN)-based approach for two different configurations. The data set for CNN training is collected by superposing the information obtained from individual antenna elements. The results of the CNN models outperform the look-up table results. The proposed approach is promising, as the phase-only optimization and phase–power-combined optimization show a 27% and 4% lower hotspot-to-target energy ratio, respectively, than the look-up table results for the linear MH applicator. The proposed deep-learning-based optimization technique can be utilized as a protocol to be applied on any MH applicator for the optimization of the antenna excitations, as well as for a comparison of MH applicators. Full article

(This article belongs to the Special Issue Advances in Medical Microwave Imaging and Signal Processing, and Hyperthermic Technologies for Healthcare)

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20 pages, 8026 KiB

Open AccessArticle

Microwave Hyperthermia of Brain Tumors: A 2D Assessment Parametric Numerical Study

by Jan Redr, Tomas Pokorny, Tomas Drizdal, Ondrej Fiser, Matous Brunat, Jan Vrba and David Vrba

Sensors 2022, 22(16), 6115; https://doi.org/10.3390/s22166115 - 16 Aug 2022

Cited by 7 | Viewed by 2763

Abstract

Due to the clinically proven benefit of hyperthermia treatments if added to standard cancer therapies for various tumor sites and the recent development of non-invasive temperature measurements using magnetic resonance systems, the hyperthermia community is convinced that it is a time when even [...] Read more.

Due to the clinically proven benefit of hyperthermia treatments if added to standard cancer therapies for various tumor sites and the recent development of non-invasive temperature measurements using magnetic resonance systems, the hyperthermia community is convinced that it is a time when even patients with brain tumors could benefit from regional microwave hyperthermia, even if they are the subject of a treatment to a vital organ. The purpose of this study was to numerically analyze the ability to achieve a therapeutically relevant constructive superposition of electromagnetic (EM) waves in the treatment of hyperthermia targets within the brain. We evaluated the effect of the target size and position, operating frequency, and the number of antenna elements forming the phased array applicator on the treatment quality. In total, 10 anatomically realistic 2D human head models were considered, in which 10 circular hyperthermia targets with diameters of 20, 25, and 30 mm were examined. Additionally, applicators with 8, 12, 16, and 24 antenna elements and operating frequencies of 434, 650, 915, and 1150 MHz, respectively, were analyzed. For all scenarios considered (4800 combinations), the EM field distributions of individual antenna elements were calculated and treatment planning was performed. Their quality was evaluated using parameters applied in clinical practice, i.e., target coverage (TC) and the target to hot-spot quotient (THQ). The 12-antenna phased array system operating at 434 MHz was the best candidate among all tested systems for HT treatments of glioblastoma tumors. The 12 antenna elements met all the requirements to cover the entire target area; an additional increase in the number of antenna elements did not have a significant effect on the treatment quality. Full article

(This article belongs to the Special Issue Advances in Medical Microwave Imaging and Signal Processing, and Hyperthermic Technologies for Healthcare)

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28 pages, 9704 KiB

Open AccessArticle

Dielectric Permittivity Measurement Using Open-Ended Coaxial Probe—Modeling and Simulation Based on the Simple Capacitive-Load Model

by Antonio Šarolić and Anđela Matković

Sensors 2022, 22(16), 6024; https://doi.org/10.3390/s22166024 - 12 Aug 2022

Cited by 14 | Viewed by 4804

Abstract

The study aim was to validate that dielectric permittivity measurement using the open-ended coaxial probe can be reliably modeled using electromagnetic modeling and simulations, followed by the postprocessing calculations based on the simple capacitive-load model. Saline solutions with various NaCl concentrations were used [...] Read more.

The study aim was to validate that dielectric permittivity measurement using the open-ended coaxial probe can be reliably modeled using electromagnetic modeling and simulations, followed by the postprocessing calculations based on the simple capacitive-load model. Saline solutions with various NaCl concentrations were used as materials under test (MUTs) to investigate how ionic conductivity affects the model validity. Two different solvers and simulation methods were used: FEKO for the frequency domain and CST for the time domain. Furthermore, we performed physical experiments with the same probe and MUTs, again implementing the capacitive-load model on the measurement data to observe the model validity. Relative error of the capacitive-load model with respect to the reference permittivity values, both in measurements and simulations, was within 10% for all cases except for the measured

ε_{r}^{'}

of 1M solution at the lowest frequencies. The model yielded average relative errors well below 1% for the physiological saline, which is relevant for biological materials. The error increased for higher concentrations and for the lowest simulated frequencies but was within the declared measurement accuracy of the probe itself. This makes the simple capacitive-load model valid for all analyzed concentrations in the microwave frequency range from 0.5 to 18 GHz. Full article

(This article belongs to the Special Issue Advances in Medical Microwave Imaging and Signal Processing, and Hyperthermic Technologies for Healthcare)

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13 pages, 2983 KiB

Open AccessArticle

MiWEndo: Evaluation of a Microwave Colonoscopy Algorithm for Early Colorectal Cancer Detection in Ex Vivo Human Colon Models

by Marta Guardiola, Walid Dghoughi, Roberto Sont, Alejandra Garrido, Sergi Marcoval, Luz María Neira, Ignasi Belda and Glòria Fernández-Esparrach

Sensors 2022, 22(13), 4902; https://doi.org/10.3390/s22134902 - 29 Jun 2022

Cited by 5 | Viewed by 2112

Abstract

This study assesses the efficacy of detecting colorectal cancer precursors or polyps in an ex vivo human colon model with a microwave colonoscopy algorithm. Nowadays, 22% of polyps go undetected with conventional colonoscopy, and the risk of cancer after a negative colonoscopy can [...] Read more.

This study assesses the efficacy of detecting colorectal cancer precursors or polyps in an ex vivo human colon model with a microwave colonoscopy algorithm. Nowadays, 22% of polyps go undetected with conventional colonoscopy, and the risk of cancer after a negative colonoscopy can be up to 7.9%. We developed a microwave colonoscopy device that consists of a cylindrical ring-shaped switchable microwave antenna array that can be attached to the tip of a conventional colonoscope as an accessory. The accessory is connected to an external unit that allows successive measurements of the colon and processes the measurements with a microwave imaging algorithm. An acoustic signal is generated when a polyp is detected. Fifteen ex vivo freshly excised human colons with cancer (n = 12) or polyps (n = 3) were examined with the microwave-assisted colonoscopy system simulating a real colonoscopy exploration. After the experiment, the dielectric properties of the specimens were measured with a coaxial probe and the samples underwent a pathology analysis. The results show that all the neoplasms were detected with a sensitivity of 100% and specificity of 87.4%. Full article

(This article belongs to the Special Issue Advances in Medical Microwave Imaging and Signal Processing, and Hyperthermic Technologies for Healthcare)

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14 pages, 4447 KiB

Open AccessArticle

Heterogeneous Skin Phantoms for Experimental Validation of Microwave-Based Diagnostic Tools

by Jasmine Boparai and Milica Popović

Sensors 2022, 22(5), 1955; https://doi.org/10.3390/s22051955 - 2 Mar 2022

Cited by 9 | Viewed by 4058

Abstract

Considerable exploration has been done in recent years to exploit the reported inherent dielectric contrast between healthy and malignant tissues for a range of medical applications. In particular, microwave technologies have been investigated towards new diagnostic medical tools. To assess the performance and [...] Read more.

Considerable exploration has been done in recent years to exploit the reported inherent dielectric contrast between healthy and malignant tissues for a range of medical applications. In particular, microwave technologies have been investigated towards new diagnostic medical tools. To assess the performance and detection capabilities of such systems, tissue-mimicking phantoms are designed for controlled laboratory experiments. We here report phantoms developed to dielectrically represent malign skin lesions such as liposarcoma and nonsyndromic multiple basal cell carcinoma. Further, in order to provide a range of anatomically realistic scenarios, and provide meaningful comparison between different phantoms, cancer-mimicking lesions are inserted into two different types of skin phantoms with varying tumor–skin geometries. These configurations were measured with a microwave dielectric probe (0.5–26.5 GHz), yielding insight into factors that could affect the performance of diagnostic and detection tools. Full article

(This article belongs to the Special Issue Advances in Medical Microwave Imaging and Signal Processing, and Hyperthermic Technologies for Healthcare)

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18 pages, 3615 KiB

Open AccessArticle

Simultaneous ThermoBrachytherapy: Electromagnetic Simulation Methods for Fast and Accurate Adaptive Treatment Planning

by Ioannis Androulakis, Rob M. C. Mestrom, Miranda E. M. C. Christianen, Inger-Karine K. Kolkman-Deurloo and Gerard C. van Rhoon

Sensors 2022, 22(4), 1328; https://doi.org/10.3390/s22041328 - 9 Feb 2022

Cited by 5 | Viewed by 1978

Abstract

The combination of interstitial hyperthermia treatment (IHT) with high dose rate brachytherapy (HDR-BT) can improve clinical outcomes since it highly enhances the efficiency of cell kill, especially when applied simultaneously. Therefore, we have developed the ThermoBrachy applicators. To effectively apply optimal targeted IHT, [...] Read more.

The combination of interstitial hyperthermia treatment (IHT) with high dose rate brachytherapy (HDR-BT) can improve clinical outcomes since it highly enhances the efficiency of cell kill, especially when applied simultaneously. Therefore, we have developed the ThermoBrachy applicators. To effectively apply optimal targeted IHT, treatment planning is considered essential. However, treatment planning in IHT is rarely applied as it is regarded as difficult to accurately calculate the deposited energy in the tissue in a short enough time for clinical practice. In this study, we investigated various time-efficient methods for fast computation of the electromagnetic (EM) energy deposition resulting from the ThermoBrachy applicators. Initially, we investigated the use of an electro-quasistatic solver. Next, we extended our investigation to the application of geometric simplifications. Furthermore, we investigated the validity of the superpositioning principle, which can enable adaptive treatment plan optimization without the need for continuous recomputation of the EM field. Finally, we evaluated the accuracy of the methods by comparing them to the golden standard Finite-Difference Time-Domain calculation method using gamma-index analysis. The simplifications considerably reduced the computation time needed, improving from >12 h to a few seconds. All investigated methods showed excellent agreement with the golden standard by showing a >99% passing rate with 1%/0.5 mm Dose Difference and Distance-to-Agreement criteria. These results allow the proposed electromagnetic simulation method to be used for fast and accurate adaptive treatment planning. Full article

(This article belongs to the Special Issue Advances in Medical Microwave Imaging and Signal Processing, and Hyperthermic Technologies for Healthcare)

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13 pages, 870 KiB

Open AccessArticle

Characterization of Open-Ended Coaxial Probe Sensing Depth with Respect to Aperture Size for Dielectric Property Measurement of Heterogeneous Tissues

by Cemanur Aydinalp, Sulayman Joof, Ismail Dilman, Ibrahim Akduman and Tuba Yilmaz

Sensors 2022, 22(3), 760; https://doi.org/10.3390/s22030760 - 19 Jan 2022

Cited by 19 | Viewed by 3701

Abstract

The open-ended coaxial probe (OECP) method is frequently used for the microwave dielectric property (DP) characterization of high permittivity and conductivity materials due to inherent advantages including minimal sample preparation requirements and broadband measurement capabilities. However, the OECP method is known to suffer [...] Read more.

The open-ended coaxial probe (OECP) method is frequently used for the microwave dielectric property (DP) characterization of high permittivity and conductivity materials due to inherent advantages including minimal sample preparation requirements and broadband measurement capabilities. However, the OECP method is known to suffer from high measurement error. One well-known contributor to the high error rates is tissue heterogeneity, which can potentially be managed through the selection of a probe with a proper sensing depth (SD). The SD of the OECP is dependent on many factors including sample DPs and probe aperture diameter. Although the effects of sample DPs on SD have been investigated to some extent in the literature, the probe aperture diameters, particularly small diameters, have not been fully explored. To this end, the SDs of probes with three different apertures (0.5, 0.9 and 2.2 mm-diameters) were analyzed in this study. Probes’ SDs were first investigated with simulations using a double-layered sample configuration (skin tissue and olive oil). Next, experiments were performed using a commercial OECP with a 2.2 mm aperture diameter. The SD was categorized based on 5%, 20% and 80% DP change. Among these threshold values, a 5% DP change was selected as the benchmark for SD categorization. The findings suggest that probes with a smaller aperture size and correspondingly smaller SD should be utilized when measuring the DPs of thin and multilayered samples, such as healthy and diseased skin tissues, to increase the measurement accuracy. Full article

(This article belongs to the Special Issue Advances in Medical Microwave Imaging and Signal Processing, and Hyperthermic Technologies for Healthcare)

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19 pages, 7511 KiB

Open AccessArticle

Open-Ended Transmission Coaxial Probes for Sarcopenia Assessment

by Paul Meaney, Shireen D. Geimer, Roberta M. diFlorio-Alexander, Robin Augustine and Timothy Raynolds

Sensors 2022, 22(3), 748; https://doi.org/10.3390/s22030748 - 19 Jan 2022

Cited by 3 | Viewed by 2113

Abstract

We developed a handheld, side-by-side transmission-based probe for interrogating tissue to diagnose sarcopenia—a condition largely characterized by muscle loss and replacement by fat. While commercial microwave reflection-based probes exist, they can only be used in a lab for a variety of applications. The [...] Read more.

We developed a handheld, side-by-side transmission-based probe for interrogating tissue to diagnose sarcopenia—a condition largely characterized by muscle loss and replacement by fat. While commercial microwave reflection-based probes exist, they can only be used in a lab for a variety of applications. The penetration depth of these probes is only in the order of 0.3 mm, which does not even traverse the skin layer, and minor motion of the coaxial feedlines can completely dismantle the calibration. Our device builds primarily on the transmission-based concept that allows for substantially greater signal penetration depth operating over a very broad bandwidth. Additional features were integrated to further improve the penetration, optimize the geometry for a more focused planar excitation, and juxtapose the coaxial apertures for more controlled interrogation. The larger coaxial apertures further increased the penetration depth while retaining the broadband performance. Three-dimensional printing technology made it possible for the apertures to be compressed into ellipses for interrogation in a near-planar geometry. Finally, fixed side-by-side positioning provided repeatable and reliable performance. The probes were also not susceptible to multipath signal corruption due to the close proximity of the transmitting and receiving apertures. The new concept worked from 100 MHz to over 8 GHz and could sense property changes as deep as 2–3 cm. While the signal changes due to deeper feature aberrations were more subtle than for signals emanating from the skin and subcutaneous fat layers, the large property contrast between muscle and fat is a sarcopenic indication that helps to distinguish even the deepest objects. This device has the potential to provide needed specificity information about the relevant underlying tissue. Full article

(This article belongs to the Special Issue Advances in Medical Microwave Imaging and Signal Processing, and Hyperthermic Technologies for Healthcare)

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27 pages, 8307 KiB

Open AccessArticle

Development of 3D MRI-Based Anatomically Realistic Models of Breast Tissues and Tumours for Microwave Imaging Diagnosis

by Ana Catarina Pelicano, Maria C. T. Gonçalves, Daniela M. Godinho, Tiago Castela, M. Lurdes Orvalho, Nuno A. M. Araújo, Emily Porter and Raquel C. Conceição

Sensors 2021, 21(24), 8265; https://doi.org/10.3390/s21248265 - 10 Dec 2021

Cited by 13 | Viewed by 3719

Abstract

Breast cancer diagnosis using radar-based medical MicroWave Imaging (MWI) has been studied in recent years. Realistic numerical and physical models of the breast are needed for simulation and experimental testing of MWI prototypes. We aim to provide the scientific community with an online [...] Read more.

Breast cancer diagnosis using radar-based medical MicroWave Imaging (MWI) has been studied in recent years. Realistic numerical and physical models of the breast are needed for simulation and experimental testing of MWI prototypes. We aim to provide the scientific community with an online repository of multiple accurate realistic breast tissue models derived from Magnetic Resonance Imaging (MRI), including benign and malignant tumours. Such models are suitable for 3D printing, leveraging experimental MWI testing. We propose a pre-processing pipeline, which includes image registration, bias field correction, data normalisation, background subtraction, and median filtering. We segmented the fat tissue with the region growing algorithm in fat-weighted Dixon images. Skin, fibroglandular tissue, and the chest wall boundary were segmented from water-weighted Dixon images. Then, we applied a 3D region growing and Hoshen-Kopelman algorithms for tumour segmentation. The developed semi-automatic segmentation procedure is suitable to segment tissues with a varying level of heterogeneity regarding voxel intensity. Two accurate breast models with benign and malignant tumours, with dielectric properties at 3, 6, and 9 GHz frequencies have been made available to the research community. These are suitable for microwave diagnosis, i.e., imaging and classification, and can be easily adapted to other imaging modalities. Full article

(This article belongs to the Special Issue Advances in Medical Microwave Imaging and Signal Processing, and Hyperthermic Technologies for Healthcare)

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15 pages, 3360 KiB

Open AccessFeature PaperArticle

An Optimization-Based Approach to Radar Image Reconstruction in Breast Microwave Sensing

by Tyson Reimer and Stephen Pistorius

Sensors 2021, 21(24), 8172; https://doi.org/10.3390/s21248172 - 7 Dec 2021

Cited by 15 | Viewed by 3047

Abstract

Breast microwave sensing (BMS) has been studied as a potential technique for cancer detection due to the observed microwave properties of malignant and healthy breast tissues. This work presents a novel radar-based image reconstruction algorithm for use in BMS that reframes the radar [...] Read more.

Breast microwave sensing (BMS) has been studied as a potential technique for cancer detection due to the observed microwave properties of malignant and healthy breast tissues. This work presents a novel radar-based image reconstruction algorithm for use in BMS that reframes the radar image reconstruction process as an optimization problem. A gradient descent optimizer was used to create an optimization-based radar reconstruction (ORR) algorithm. Two hundred scans of MRI-derived breast phantoms were performed with a preclinical BMS system. These scans were reconstructed using the ORR, delay-and-sum (DAS), and delay-multiply-and-sum (DMAS) beamformers. The ORR was observed to improve both sensitivity and specificity compared to DAS and DMAS. The estimated sensitivity and specificity of the DAS beamformer were 19% and 44%, respectively, while for ORR, they were 27% and 56%, representing a relative increase of 42% and 27%. The DAS reconstructions also exhibited a hot-spot image artifact, where a localized region of high intensity that did not correspond to any physical phantom feature would be present in an image. This artifact appeared like a tumour response within the image and contributed to the lower specificity of the DAS beamformer. This artifact was not observed in the ORR reconstructions. This work demonstrates the potential of an optimization-based conceptualization of the radar image reconstruction problem in BMS. The ORR algorithm implemented in this work showed improved diagnostic performance and fewer image artifacts compared to the widely employed DAS algorithm. Full article

(This article belongs to the Special Issue Advances in Medical Microwave Imaging and Signal Processing, and Hyperthermic Technologies for Healthcare)

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15 pages, 2659 KiB

Open AccessArticle

Assessing Patient-Specific Microwave Breast Imaging in Clinical Case Studies

by Declan O’Loughlin, Muhammad Adnan Elahi, Benjamin R. Lavoie, Elise C. Fear and Martin O’Halloran

Sensors 2021, 21(23), 8048; https://doi.org/10.3390/s21238048 - 1 Dec 2021

Cited by 5 | Viewed by 2378

Abstract

Microwave breast imaging has seen increasing use in clinical investigations in the past decade with over eight systems having being trialled with patients. The majority of systems use radar-based algorithms to reconstruct the image shown to the clinician which requires an estimate of [...] Read more.

Microwave breast imaging has seen increasing use in clinical investigations in the past decade with over eight systems having being trialled with patients. The majority of systems use radar-based algorithms to reconstruct the image shown to the clinician which requires an estimate of the dielectric properties of the breast to synthetically focus signals to reconstruct the image. Both simulated and experimental studies have shown that, even in simplified scenarios, misestimation of the dielectric properties can impair both the image quality and tumour detection. Many methods have been proposed to address the issue of the estimation of dielectric properties, but few have been tested with patient images. In this work, a leading approach for dielectric properties estimation based on the computation of many candidate images for microwave breast imaging is analysed with patient images for the first time. Using five clinical case studies of both healthy breasts and breasts with abnormalities, the advantages and disadvantages of computational patient-specific microwave breast image reconstruction are highlighted. Full article

(This article belongs to the Special Issue Advances in Medical Microwave Imaging and Signal Processing, and Hyperthermic Technologies for Healthcare)

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13 pages, 2967 KiB

Open AccessArticle

Controlled Measurement Setup for Ultra-Wideband Dielectric Modeling of Muscle Tissue in 20–45 °C Temperature Range

by Gertjan Maenhout, Tomislav Markovic and Bart Nauwelaers

Sensors 2021, 21(22), 7644; https://doi.org/10.3390/s21227644 - 17 Nov 2021

Cited by 3 | Viewed by 2408

Abstract

In order to design electromagnetic applicators for diagnostic and therapeutic applications, an adequate dielectric tissue model is required. In addition, tissue temperature will heavily influence the dielectric properties and the dielectric model should, thus, be extended to incorporate this temperature dependence. Thus, this [...] Read more.

In order to design electromagnetic applicators for diagnostic and therapeutic applications, an adequate dielectric tissue model is required. In addition, tissue temperature will heavily influence the dielectric properties and the dielectric model should, thus, be extended to incorporate this temperature dependence. Thus, this work has a dual purpose. Given the influence of temperature, dehydration, and probe-to-tissue contact pressure on dielectric measurements, this work will initially present the first setup to actively control and monitor the temperature of the sample, the dehydration rate of the investigated sample, and the applied probe-to-tissue contact pressure. Secondly, this work measured the dielectric properties of porcine muscle in the 0.5–40 GHz frequency range for temperatures from 20 °C to 45 °C. Following measurements, a single-pole Cole–Cole model is presented, in which the five Cole–Cole parameters (

ϵ_{\infty}

,

σ_{s}

,

Δ ϵ

,

τ

, and

α

) are given by a first order polynomial as function of tissue temperature. The dielectric model closely agrees with the limited dielectric models known in literature for muscle tissue at 37 °C, which makes it suited for the design of in vivo applicators. Furthermore, the dielectric data at 41–45 °C is of great importance for the design of hyperthermia applicators. Full article

(This article belongs to the Special Issue Advances in Medical Microwave Imaging and Signal Processing, and Hyperthermic Technologies for Healthcare)

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17 pages, 4788 KiB

Open AccessArticle

Monitoring Bone Density Using Microwave Tomography of Human Legs: A Numerical Feasibility Study

by Mohanad Alkhodari, Amer Zakaria and Nasser Qaddoumi

Sensors 2021, 21(21), 7078; https://doi.org/10.3390/s21217078 - 26 Oct 2021

Cited by 9 | Viewed by 2720

Abstract

A major cause of bone mass loss worldwide is osteoporosis. X-ray is considered to be the gold-standard technique to diagnose this disease. However, there is currently a need for an alternative modality due to the ionizing radiations used in X-rays. In this vein, [...] Read more.

A major cause of bone mass loss worldwide is osteoporosis. X-ray is considered to be the gold-standard technique to diagnose this disease. However, there is currently a need for an alternative modality due to the ionizing radiations used in X-rays. In this vein, we conducted a numerical study herein to investigate the feasibility of using microwave tomography (MWT) to detect bone density variations that are correlated to variations in the complex relative permittivity within the reconstructed images. This study was performed using an in-house finite-element method contrast source inversion algorithm (FEM-CSI). Three anatomically-realistic human leg models based on magnetic resonance imaging reconstructions were created. Each model represents a leg with a distinct fat layer thickness; thus, the three models are for legs with thin, medium, and thick fat layers. In addition to using conventional matching media in the numerical study, the use of commercially available and cheap ultrasound gel was evaluated prior to bone image analysis. The inversion algorithm successfully localized bones in the thin and medium fat scenarios. In addition, bone volume variations were found to be inversely proportional to their relative permittivity in the reconstructed images with the root mean square error as low as 2.54. The observations found in this study suggest MWT as a promising bone imaging modality owing to its safe and non-ionizing radiations used in imaging objects with high quality. Full article

(This article belongs to the Special Issue Advances in Medical Microwave Imaging and Signal Processing, and Hyperthermic Technologies for Healthcare)

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13 pages, 3470 KiB

Open AccessArticle

Application of Machine Learning to Predict Dielectric Properties of In Vivo Biological Tissue

by Branislav Gerazov, Daphne Anne Caligari Conti, Laura Farina, Lourdes Farrugia, Charles V. Sammut, Pierre Schembri Wismayer and Raquel C. Conceição

Sensors 2021, 21(20), 6935; https://doi.org/10.3390/s21206935 - 19 Oct 2021

Cited by 4 | Viewed by 2267

Abstract

In this paper we revisited a database with measurements of the dielectric properties of rat muscles. Measurements were performed both in vivo and ex vivo; the latter were performed in tissues with varying levels of hydration. Dielectric property measurements were performed with an [...] Read more.

In this paper we revisited a database with measurements of the dielectric properties of rat muscles. Measurements were performed both in vivo and ex vivo; the latter were performed in tissues with varying levels of hydration. Dielectric property measurements were performed with an open-ended coaxial probe between the frequencies of 500 MHz and 50 GHz at a room temperature of 25 °C. In vivo dielectric properties are more valuable for creating realistic electromagnetic models of biological tissue, but these are more difficult to measure and scarcer in the literature. In this paper, we used machine learning models to predict the in vivo dielectric properties of rat muscle from ex vivo dielectric property measurements for varying levels of hydration. We observed promising results that suggest that our model can make a fair estimation of in vivo properties from ex vivo properties. Full article

(This article belongs to the Special Issue Advances in Medical Microwave Imaging and Signal Processing, and Hyperthermic Technologies for Healthcare)

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29 pages, 2273 KiB

Open AccessReview

Review of Thermal and Physiological Properties of Human Breast Tissue

by Jeantide Said Camilleri, Lourdes Farrugia, Sergio Curto, Dario B. Rodrigues, Laura Farina, Gordon Caruana Dingli, Julian Bonello, Iman Farhat and Charles V. Sammut

Sensors 2022, 22(10), 3894; https://doi.org/10.3390/s22103894 - 20 May 2022

Cited by 19 | Viewed by 6381

Abstract

Electromagnetic thermal therapies for cancer treatment, such as microwave hyperthermia, aim to heat up a targeted tumour site to temperatures within 40 and 44 °C. Computational simulations used to investigate such heating systems employ the Pennes’ bioheat equation to model the heat exchange [...] Read more.

Electromagnetic thermal therapies for cancer treatment, such as microwave hyperthermia, aim to heat up a targeted tumour site to temperatures within 40 and 44 °C. Computational simulations used to investigate such heating systems employ the Pennes’ bioheat equation to model the heat exchange within the tissue, which accounts for several tissue properties: density, specific heat capacity, thermal conductivity, metabolic heat generation rate, and blood perfusion rate. We present a review of these thermal and physiological properties relevant for hyperthermia treatments of breast including fibroglandular breast, fatty breast, and breast tumours. The data included in this review were obtained from both experimental measurement studies and estimated properties of human breast tissues. The latter were used in computational studies of breast thermal treatments. The measurement methods, where available, are discussed together with the estimations and approximations considered for values where measurements were unavailable. The review concludes that measurement data for the thermal and physiological properties of breast and tumour tissue are limited. Fibroglandular and fatty breast tissue properties are often approximated from those of generic muscle or fat tissue. Tumour tissue properties are mostly obtained from approximating equations or assumed to be the same as those of glandular tissue. We also present a set of reliable data, which can be used for more accurate modelling and simulation studies to better treat breast cancer using thermal therapies. Full article

(This article belongs to the Special Issue Advances in Medical Microwave Imaging and Signal Processing, and Hyperthermic Technologies for Healthcare)

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