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

Abstract

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

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

“…Skin Debye parameters were obtained from published data in Zastrow et al [ 30 ], healthy and malignant ALNs were modeled according to the dielectric properties found in studies by Cameron et al [ 2 ], the dielectric properties for healthy tissue were based on the adipose tissue measurements described by Lazebnik et al [ 31 ] and the muscle properties were based on those described by Gabriel et al [ 32 ]. Although new insights about ALN average dielectric properties have been provided [ 33 , 34 ], in this paper we considered ALN heterogeneity within the models. A dielectric variation of was randomly incorporated to 4-mm-side squares below the skin to mimic normal tissue heterogeneity.…”

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

“…This approach facilitated the mapping of the T1-w Dixon-W voxel intensities to the tissue's dielectric property curves. It is important to note that T1-w Dixon-W signal intensities are directly proportional to the amount of hydrogen nuclei in the tissues, implying that higher voxel intensities correspond to greater water content in the tissues [56].…”

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

“…A summary of previously developed methodologies to create breast models has been recently published in [35].…”