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.info:eu-repo/semantics/publishedVersio

The imaging of malignant pancreatic tumors

As neoplasias malignas do pâncreas englobam vários tipos histologicos com características ima giológicas e comportamentos que permitem distingui-los entre si numa boa percentagem de situações. Contudo, nem sempre a sua diferenciação se toma possível sem o recurso às técnicas anátomo-patoló gicas, constituindo um grande desafio à imagiologia o diagnóstico diferencial com lesões benignas, com referencia particular às massas inflamatórias. O adenocarcinoma constitui cerca de 95% das neo plasias pancreáticas e é uma das grandes causas de morte por cancro nos países desenvolvidos. As técnicas de imagem aplicadas no diagnóstico e no estadiamento dos principais tumores do pâncreas são muito diversificadas, englobando meios inócuos, como a ecografia, métodos invasivos utilizando técnicas angiográficas ou recurso aos meios endoscópicos para acesso endocavitário. A utilidade de cada uma destas variedades técnicas depende essencialmente do tipo de tumor a estudar, tomando-se fundamental o correcto e o completo conhecimento das possibilidades e limitações de cada uma, com vista à aplicação racional dos meios na imagiologia do pâncreas.Malignant neoplasias of the pancreas include various histological types with imaging charac teristics and behaviour which allows them to be distinguished from one another in a good percen tage of situations. However, differentiation is not always possible without resorting to anatomo -pathological techniques, differential diagnosis with benign lesions being a great challenge to ima ging, with particular reference to the inflammatory masses. Adenocarcinoma makes up about 95% of pancreatic neoplasias and is one of the great causes of death by cancer in developed countries. The imaging techniques applied in the diagnosis and staging of the principal tumours of the pan creas are very diversified, including innocuous means such as ultrasound, invasive methods using angiographic techniques or the recourse to endoscopic means to endocavity accessment. The use of each of these techniques depends essentially on the type of tumor to be studied, the correct and complete knowledge ofthe possibilities and limitations ofeach one, becomes fundamental in what concerns the rational application ofmeans in the imaging ofthe pancreas