Evaluating the Performance of Algorithms in Axillary Microwave Imaging towards Improved Breast Cancer Staging.

Breast cancer is the most common and the fifth deadliest cancer worldwide. In more advanced stages of cancer, cancer cells metastasize through lymphatic and blood vessels. Currently there is no satisfactory neoadjuvant (i.e., preoperative) diagnosis to assess whether cancer has spread to neighboring Axillary Lymph Nodes (ALN). This paper addresses the use of radar Microwave Imaging (MWI) to detect and determine whether ALNs have been metastasized, presenting an analysis of the performance of different artifact removal and beamformer algorithms in distinct anatomical scenarios. We assess distinct axillary region models and the effect of varying the shape of the skin, muscle and subcutaneous adipose tissue layers on single ALN detection. We also study multiple ALN detection and contrast between healthy and metastasized ALNs. We propose a new beamformer algorithm denominated Channel-Ranked Delay-Multiply-And-Sum (CR-DMAS), which allows the successful detection of ALNs in order to achieve better Signal-to-Clutter Ratio, e.g., with the muscle layer up to 3.07 dB, a Signal-to-Mean Ratio of up to 20.78 dB and a Location Error of 1.58 mm. In multiple target detection, CR-DMAS outperformed other well established beamformers used in the context of breast MWI. Overall, this work provides new insights into the performance of algorithms in axillary MWI.

Biometric Recognition: A Systematic Review on Electrocardiogram Data Acquisition Methods.

In the last decades, researchers have shown the potential of using Electrocardiogram (ECG) as a biometric trait due to its uniqueness and hidden nature. However, despite the great number of approaches found in the literature, no agreement exists on the most appropriate methodology. This paper presents a systematic review of data acquisition methods, aiming to understand the impact of some variables from the data acquisition protocol of an ECG signal in the biometric identification process. We searched for papers on the subject using Scopus, defining several keywords and restrictions, and found a total of 121 papers. Data acquisition hardware and methods vary widely throughout the literature. We reviewed the intrusiveness of acquisitions, the number of leads used, and the duration of acquisitions. Moreover, by analyzing the literature, we can conclude that the preferable solutions include: (1) the use of off-the-person acquisitions as they bring ECG biometrics closer to viable, unconstrained applications; (2) the use of a one-lead setup; and (3) short-term acquisitions as they required fewer numbers of contact points, making the data acquisition of benefit to user acceptance and allow faster acquisitions, resulting in a user-friendly biometric system. Thus, this paper reviews data acquisition methods, summarizes multiple perspectives, and highlights existing challenges and problems. In contrast, most reviews on ECG-based biometrics focus on feature extraction and classification methods.

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

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.

Initial Study Using Electrocardiogram for Authentication and Identification.

Recently, several studies have demonstrated the potential of electrocardiogram (ECG) to be used as a physiological signature for biometric systems (BS). We investigated the potential of ECG as a biometric trait for the identification and authentication of individuals. We used data from a public database, CYBHi, containing two off-the-person records from 63 subjects, separated by 3 months. For the BS, two templates were generated: (1) cardiac cycles (CC) and (2) scalograms. The identification with CC was performed with LDA, kNN, DT, and SVM, whereas a convolutional neural network (CNN) and a distance-based algorithm were used for scalograms. The authentication was performed with a distance-based algorithm, with a leave-one-out cross validation, for impostors evaluation. The identification system yielded accuracies of 79.37% and 69.84% for CC with LDA and scalograms with CNN, respectively. The authentication yielded an accuracy of 90.48% and an impostor score of 13.06% for CC, and it had an accuracy of 98.42% and an impostor score of 14.34% for scalograms. The obtained results support the claim that ECG can be successfully used for personal recognition. To the best of our knowledge, our study is the first to thoroughly compare templates and methodologies to optimize the performance of an ECG-based biometric system.

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

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.

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

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.

Development of a 3D Anthropomorphic Phantom Generator for Microwave Imaging Applications of the Head and Neck Region.

The development of 3D anthropomorphic head and neck phantoms is of crucial and timely importance to explore novel imaging techniques, such as radar-based MicroWave Imaging (MWI), which have the potential to accurately diagnose Cervical Lymph Nodes (CLNs) in a neoadjuvant and non-invasive manner. We are motivated by a significant diagnostic blind-spot regarding mass screening of LNs in the case of head and neck cancer. The timely detection and selective removal of metastatic CLNs will prevent tumor cells from entering the lymphatic and blood systems and metastasizing to other body regions. The present paper describes the developed phantom generator which allows the anthropomorphic modelling of the main biological tissues of the cervical region, including CLNs, as well as their dielectric properties, for a frequency range from 1 to 10 GHz, based on Magnetic Resonance images. The resulting phantoms of varying complexity are well-suited to contribute to all stages of the development of a radar-based MWI device capable of detecting CLNs. Simpler models are essential since complexity could hinder the initial development stages of MWI devices. Besides, the diversity of anthropomorphic phantoms resulting from the developed phantom generator can be explored in other scientific contexts and may be useful to other medical imaging modalities.

Characterisation of Ex Vivo Liver Thermal Properties for Electromagnetic-Based Hyperthermic Therapies.

Electromagnetic-based hyperthermic therapies induce a controlled increase of temperature in a specific tissue target in order to increase the tissue perfusion or metabolism, or even to induce cell necrosis. These therapies require accurate knowledge of dielectric and thermal properties to optimise treatment plans. While dielectric properties have been well investigated, only a few studies have been conducted with the aim of understanding the changes of thermal properties as a function of temperature; i.e., thermal conductivity, volumetric heat capacity and thermal diffusivity. In this study, we experimentally investigate the thermal properties of ex vivo ovine liver in the hyperthermic temperature range, from 25 °C to 97 °C. A significant increase in thermal properties is observed only above 90 °C. An analytical model is developed to model the thermal properties as a function of temperature. Thermal properties are also investigated during the natural cooling of the heated tissue. A reversible phenomenon of the thermal properties is observed; during the cooling, thermal properties followed the same behaviour observed in the heating process. Additionally, tissue density and water content are evaluated at different temperatures. Density does not change with temperature; mass and volume losses change proportionally due to water vaporisation. A 30% water loss was observed above 90 °C.

Development of an Anthropomorphic Phantom of the Axillary Region for Microwave Imaging Assessment.

We produced an anatomically and dielectrically realistic phantom of the axillary region to enable the experimental assessment of Axillary Lymph Node (ALN) imaging using microwave imaging technology. We segmented a thoracic Computed Tomography (CT) scan and created a computer-aided designed file containing the anatomical configuration of the axillary region. The phantom comprises five 3D-printed parts representing the main tissues of interest of the axillary region for the purpose of microwave imaging: fat, muscle, bone, ALNs, and lung. The phantom allows the experimental assessment of multiple anatomical configurations, by including ALNs of different size, shape, and number in several locations. Except for the bone mimicking organ, which is made of solid conductive polymer, we 3D-printed cavities to represent the fat, muscle, ALN, and lung and filled them with appropriate tissue-mimicking liquids. Existing studies about complex permittivity of ALNs have reported limitations. To address these, we measured the complex permittivity of both human and animal lymph nodes using the standard open-ended coaxial-probe technique, over the 0.5 GHz-8.5 GHz frequency band, thus extending current knowledge on dielectric properties of ALNs. Lastly, we numerically evaluated the effect of the polymer which constitutes the cavities of the phantom and compared it to the realistic axillary region. The results showed a maximum difference of 7 dB at 4 GHz in the electric field magnitude coupled to the tissues and a maximum of 10 dB difference in the ALN response. Our results showed that the phantom is a good representation of the axillary region and a viable tool for pre-clinical assessment of microwave imaging technology.

Gamma Distribution Model in the Evaluation of Breast Cancer Through Diffusion-Weighted MRI: A Preliminary Study.

BACKGROUND: The gamma distribution (GD) model is based on the statistical distribution of the apparent diffusion coefficient (ADC) parameter. The GD model is expected to reflect the probability of the distribution of water molecule mobility in different regions of tissue, but also the intra- and extracellular diffusion and perfusion components (f1 , f2 , f3 fractions). PURPOSE: To assess the GD model in the characterization and diagnostic performance of breast lesions. STUDY TYPE: Prospective. POPULATION: In all, 48 females with 24 benign and 33 malignant breast lesions. FIELD STRENGTH/SEQUENCE: A diffusion-weighted sequence (b = 0-3000 s/mm2 ) with a 3 T scanner. ASSESSMENT: For each group of benign, malignant, invasive, and in situ breast lesions, the ADC was obtained. Also, θ and k parameters (scale and shape of the statistic distribution, respectively), f1 , f2 , and f3 fractions were obtained from fitting the GD model to diffusion data. STATISTICAL TESTS: Lesion types were compared regarding diffusion parameters using nonparametric statistics and receiver operating characteristic curve diagnostic performance. RESULTS: The majority of GD parameters (k, f1 , f2 , f3 fractions) showed significant differences between benign and malignant lesions, and between in situ and invasive lesions (f1 , f2 , f3 fractions) (P ≤ 0.001). The best diagnostic performances were obtained with ADC and f1 fraction in benign vs. malignant lesions (area under curve [AUC] = 0.923 and 0.913, sensitivity = 93.9% and 81.8%, specificity = 79.2% and 91.7%, accuracy = 87.7% and 86.0%, respectively). In invasive lesions vs. in situ lesions, the best diagnostic performance was obtained with f1 fraction, which outperformed ADC results (AUC = 0.978 and 0.941, and sensitivity = 91.3% for both parameters, specificity = 100.0% and 90.0%, accuracy = 93.9% and 90.9%, respectively). DATA CONCLUSION: This work shows that the GD model provides information in addition to the ADC parameter, suggesting its potential in the diagnosis of breast lesions. Level of Evidence 2: Technical Efficacy Stage 2 J. Magn. Reson. Imaging 2019;50:230-238.

Physical activity levels and hepatic steatosis: A longitudinal follow-up study in adults.

BACKGROUND AND AIM: This study aimed to evaluate the impact of physical activity (PA) on the course of hepatic steatosis (HS) in adults. METHODS: Hepatic steatosis status (ultrasonography) and PA levels were evaluated in 5860 subjects at baseline and after approximately 2.5 years (range: 19-50 months). At follow up, possible exposures to different PA levels were those who remained inactive, became inactive, became active, and remained active. After follow up, subjects were then classified according to the four possible states (outcomes): "remained without HS," "developed HS" (subjects without HS at baseline), "remained with HS," or "reverted HS." RESULTS: After multivariate adjustments, individuals without HS that became or remained physically active were less likely to develop HS compared with those who remained physically inactive (odds ratio = 0.75, P = 0.04 and 0.75, P = 0.03, respectively). Among those with HS at baseline, becoming and remaining physically active beneficially improved the HS status (odds ratio = 0.64, P = 0.01 and 0.66, P = 0.01, respectively). However, the significance was lost when adjusted for changes in body mass index. CONCLUSION: Higher levels of PA were associated with prevention and treatment of HS, with evidence of effect mediation by changes in body mass index.

Obesity Modifies the Effect of Fitness on Heart Rate Indices during Exercise Stress Testing in Asymptomatic Individuals.

OBJECTIVE: To assess the impact of aerobic fitness on exercise heart rate (HR) indices in an asymptomatic cohort across different body mass index (BMI) categories. METHODS: We performed a cross-sectional analysis of 506 working-class Brazilian subjects, free of known clinical cardiovascular disease(e.g. ischemic heart disease and stroke) who underwent an exercise stress test. RESULTS: There was a significant trend towards decreased HR at peak exercise, HR recovery and chronotropic index (CI) measures as BMI increased, but resting HR increased significantly across BMI categories. In multivariate analysis, the change in CI per unit change in metabolic equivalents of task was greater among the obese subjects than the normal-weight (2.7 vs. ­0.07; p interaction = 0.029)and overweight (2.7 vs. 0.7; p interaction = 0.044) subjects. A similar pattern was seen with peak HR and HR recovery, although the formal tests of interaction did not achieve statistical significance. CONCLUSION: Our findings strongly suggest that fitness is associated with a favorable HR profile and is modified by BMI. Intervention programs should place emphasis on fitness and not only on weight loss.

Prostate-specific antigen testing in men between 40 and 70 years in Brazil: database from a check-up program.

OBJECTIVES: To evaluate the PSA in a large population of Brazilian men undergone to check up, and correlate the PSA cutoffs with prostate size and urinary symptoms. MATERIALS AND METHODS: This is a cross sectional study performed with men between 40 and 70 years undergone to check-up. All men were undergone to urological evaluation, digital rectal examination, prostate-specific antigen, and ultrasonography The exclusion criteria were men who used testosterone in the last six months, or who were using 5 alpha-reductase inhibitors. RESULTS: A total of 5015 men with an average age of 49.0 years completed the study. Most men were white and asymptomatic. The PSA in the three different aging groups were 0.9 ± 0.7 ng/dL for men between 40 and 50; 1.2 ± 0.5 ng/dL for men between 50 and 60; and 1.7 ± 1.5 ng/dL for men greater than 60 years (p=0.001). A total of 192 men had PSA between 2.5 and 4 ng/ml. From these men 130 were undergone to prostate biopsy. The predictive positive value of biopsy was 25% (32/130). In the same way, 100 patients had PSA > 4 ng/mL. From these men, 80 were undergone to prostate biopsy. In this group, the predictive positive value of biopsy was 40% (32/100). The Gleason score was 6 in 19 men (60%), 7 in 10 men (31%) and 8 in 3 men (9%). CONCLUSIONS: The PSA level of Brazilian men undergone to check up was low. There was a positive correlation with aging, IPSS and prostate size.

Repository of MRI-derived models of the breast with single and multiple benign and malignant tumors for microwave imaging research.

The diagnosis of breast cancer through MicroWave Imaging (MWI) technology has been extensively researched over the past few decades. However, continuous improvements to systems are needed to achieve clinical viability. To this end, the numerical models employed in simulation studies need to be diversified, anatomically accurate, and also representative of the cases in clinical settings. Hence, we have created the first open-access repository of 3D anatomically accurate numerical models of the breast, derived from 3.0T Magnetic Resonance Images (MRI) of benign breast disease and breast cancer patients. The models include normal breast tissues (fat, fibroglandular, skin, and muscle tissues), and benign and cancerous breast tumors. The repository contains easily reconfigurable models which can be tumor-free or contain single or multiple tumors, allowing complex and realistic test scenarios needed for feasibility and performance assessment of MWI devices prior to experimental and clinical testing. It also includes an executable file which enables researchers to generate models incorporating the dielectric properties of breast tissues at a chosen frequency ranging from 3 to 10 GHz, thereby ensuring compatibility with a wide spectrum of research requirements and stages of development for any breast MWI prototype system. Currently, our dataset comprises MRI scans of 55 patients, but new exams will be continuously added.

Uroflowmetry in a large population of Brazilian men submitted to a health check up program and its correlation with IPSS and prostate size.

PURPOSE: The aim of this study was to assess the uroflowmetry data in a large population of asymptomatic Brazilian men submitted to a health check up program and their correlation to IPSS and prostate size. MATERIALS AND METHODS: Asymptomatic men underwent a health check-up program between January and December 2012. The inclusion criteria were men between 40 and 70 years, IPSS ≤ 7, without bladder, prostate, urethral surgery, neurological diseases, urinary tract infection, PSA < 4.0 ng/dL and urinary volume higher than 150 mL. Urological assessment consisted of clinical history, IPSS, digital rectal examination (DRE), prostate specific antigen (PSA), urinalysis, ultrasonography and uroflowmetry. RESULTS: A total of 1041 asymptomatic men were included in this study. The average age was 49 years and average maximum flow rate was 17.4 mL/s. In spite of IPSS and prostate size increase with aging, they had a weak correlation with Qmax cutoffs (10 mL/s and 15 mL/s). A total of 85 men (8.3%) had more than 60 years, and even in this group, Qmax was higher than 15 mL/s. Out of 1041 men, 117 had IPSS less than 8 and Qmax less than 10 mL/s. CONCLUSIONS: In asymptomatic men there is a weak correlation between IPSS, prostate size and uroflowmetric data. The establishment of different normal cutoffs seems to be complicated and uroflowmetry data should be interpreted with caution in order to avoid misdiagnosis.

Hepatic steatosis, obesity, and the metabolic syndrome are independently and additively associated with increased systemic inflammation.

OBJECTIVE: The goal of this study was to assess the independent and collective associations of hepatic steatosis, obesity, and the metabolic syndrome with elevated high-sensitivity C-reactive protein (hs-CRP) levels. METHODS AND RESULTS: We evaluated 2388 individuals without clinical cardiovascular disease between December 2004 and December 2006. Hepatic steatosis was diagnosed by ultrasound, and the metabolic syndrome was defined using National Heart, Lung, and Blood Institute criteria. The cut point of ≥3 mg/L was used to define high hs-CRP. Multivariate logistic regression was used to assess the independent and collective associations of hepatic steatosis, obesity, and the metabolic syndrome with high hs-CRP. Steatosis was detected in 32% of participants, 23% met criteria for metabolic syndrome, and 17% were obese. After multivariate regression, hepatic steatosis (odds ratio [OR] 2.07; 95% CI 1.68 to 2.56), obesity (OR 3.00; 95% CI 2.39 to 3.80), and the metabolic syndrome (2.39; 95% CI 1.88 to 3.04) were all independently associated with high hs-CRP. Combinations of these factors were associated with an additive increase in the odds of high hs-CRP, with individuals with 1, 2, and 3 factors having ORs for high hs-CRP of 1.92 (1.49 to 2.48), 3.38 (2.50 to 4.57), and 4.53 (3.23 to 6.35), respectively. CONCLUSIONS: Hepatic steatosis, obesity, and the metabolic syndrome are independently and additively associated with increased odds of high hs-CRP levels.

Modelling level I Axillary Lymph Nodes depth for Microwave Imaging.

PURPOSE: Patient-specific information on the depth of Axillary Lymph Nodes (ALNs) is important for the development of new diagnostic imaging technologies, e.g. Microwave Imaging (MWI), aiming to assess the diagnosis of ALNs during breast cancer staging. Studies about ALNs depth have been presented for treatment planning, but they lack information on sample size and usability of the data to infer the depth of ALNs. The aim of this study was to create a mathematical model that can be used to predict a depth interval where level I ALNs are likely to be located. METHODS: We extracted biometric features of 98 patients who underwent breast Magnetic Resonance Imaging (MRI) to train two types of regression models. We then tested different combination of features to predict ALNs depth and found the best predictor. The final prediction models were then implemented in an algorithm used for MWI and tested with anthropomorphic phantoms of the axillary region. RESULTS: Body Mass Index (BMI) was the feature with best performance to predict ALNs depth with coefficient of determination (R2) ranging from 0.49 to 0.55 and Root Mean Squared Error (RMSE) ranging from 0.68 to 0.91 cm. The proposed model showed satisfactory results in microwave images of patients with different BMIs. CONCLUSIONS: The presented results contribute to the development of reconstruction algorithms for new imaging technologies and to the assessment of ALNs in other medical applications.

Incidence, risk factors and ERCP outcome for biliary complications after cadaveric OLT.

BACKGROUND/AIMS: Biliary complications (BC) occur in up to 39.5% of patients after orthotopic liver transplantation (OLT), being an important source of post-transplant morbidity. The aim is to evaluate the incidence of BC after OLT, associated risk factors and outcome after endoscopic treatment. METHODOLOGY: A retrospective case series between June 2005 and December 2008, including 195 patients that underwent 216 OLT from deceased donors. Thirty-one patients (14.3%) presented at least 1 BC, anastomotic stricture being the most frequent (83.8%). Non-anastomotic stricture was present in 1 (3.2%) and anastomotic fistula in 1. One patient presented anastomotic disconnection at ERCP. RESULTS: BC occurred 94.6 (7-487) days after OLT. Twenty-seven patients underwent endoscopic treatment, on average 2.6 ERCPs were performed per patient. Global endoscopic treatment success rate was 77.3%; being 73.7% for stenosis and 100% (3/3) for anastomotic fistula with stenosis. Recurrence of biliary stricture was observed in 3 patients, all referred to endoscopic re-treatment. ERCP complications: 2 (2.8%) stent migrations, 1 (1.4%) early stent occlusion, 1 (1.4%) respiratory distress and 1(1.4%) severe acute pancreatitis and death. There was no correlation between studied risk factors and BC's occurrence. CONCLUSION: ERCP was effective for the treatment of BC after OLT. Studied risk factors had no correlation with BC.

Development of MRI-based axillary numerical models and estimation of axillary lymph node dielectric properties for microwave imaging.

PURPOSE: Microwave imaging (MWI) has been studied as a complementary imaging modality to improve sensitivity and specificity of diagnosis of axillary lymph nodes (ALNs), which can be metastasized by breast cancer. The feasibility of such a system is based on the dielectric contrast between healthy and metastasized ALNs. However, reliable information such as anatomically realistic numerical models and matching dielectric properties of the axillary region and ALNs, which are crucial to develop MWI systems, are still limited in the literature. The purpose of this work is to develop a methodology to infer dielectric properties of structures from magnetic resonance imaging (MRI), in particular, ALNs. We further use this methodology, which is tailored for structures farther away from MR coils, to create MRI-based numerical models of the axillary region and share them with the scientific community, through an open-access repository. METHODS: We use a dataset of breast MRI scans of 40 patients, 15 of them with metastasized ALNs. We apply image processing techniques to minimize the artifacts in MR images and segment the tissues of interest. The background, lung cavity, and skin are segmented using thresholding techniques and the remaining tissues are segmented using a K-means clustering algorithm. The ALNs are segmented combining the clustering results of two MRI sequences. The performance of this methodology was evaluated using qualitative criteria. We then apply a piecewise linear interpolation between voxel signal intensities and known dielectric properties, which allow us to create dielectric property maps within an MRI and consequently infer ALN properties. Finally, we compare healthy and metastasized ALN dielectric properties within and between patients, and we create an open-access repository of numerical axillary region numerical models which can be used for electromagnetic simulations. RESULTS: The proposed methodology allowed creating anatomically realistic models of the axillary region, segmenting 80 ALNs and analyzing the corresponding dielectric properties. The estimated relative permittivity of those ALNs ranged from 16.6 to 49.3 at 5 GHz. We observe there is a high variability of dielectric properties of ALNs, which can be mainly related to the ALN size and, consequently, its composition. We verified an average dielectric contrast of 29% between healthy and metastasized ALNs. Our repository comprises 10 numerical models of the axillary region, from five patients, with variable number of metastasized ALNs and body mass index. CONCLUSIONS: The observed contrast between healthy and metastasized ALNs is a good indicator for the feasibility of a MWI system aiming to diagnose ALNs. This paper presents new contributions regarding anatomical modeling and dielectric properties' characterization, in particular for axillary region applications.

Study of the Refraction Effects in Microwave Breast Imaging Using a Dry Setup.

Medical Microwave Imaging (MWI) has been studied as a technique to aid breast cancer diagnosis. Several different prototypes have been proposed but most of them require the use of a coupling medium between the antennas and the breast, in order to reduce skin backscattering and avoid refraction effects. The use of dry setups has been addressed and recent publications show promising results. In this paper, we assess the importance of considering refraction effects in the image reconstruction algorithms. To this end, we consider a simplified homogeneous spherical model of the breast and analytically compute the propagating rays through the air-body interface. The comparison of results considering only direct ray propagation or refracted rays shows negligible impact on the accuracy of the images for moderately high permittivity media. Thus, we may avoid the computational burden of calculating the refracted rays in convex shapes.