On the Physical Interaction of Electromagnetic Waves with Human Tissues: Specific Absorption Rate (SAR) Analysis of Portable Sources – Dielectric Characterization of Breast Tissues as Pre-pathological Aid in Early Tumour Detection

This dissertation aims to investigate the interaction between electromagnetic fields and biological tissues for accurate dosimetric evaluations, as well as the application of an electromagnetic characterization system as a diagnostic tool. Specifically, the thesis focuses on two main topics: the former refers to the analysis of the specific absorption rate (SAR) of high-power (60 W), portable, and broadband EM sources. This type of instrumentation is commonly found in military equipment, such as communication backpack systems. The research aims to evaluate the impact of such radiant systems on human body. Therefore, the ultimate goal is to investigate how such devices affect the SAR in subject with different body shapes and genders and to provide guidelines for reducing the SAR levels. The latter topic focuses on the dielectric characterization of breast tissues as a pre-pathological diagnostic aid for early cancer detection, investigating two applications of a wideband characterization system based on a custom-designed open-ended coaxial probe. The first application involves the electromagnetic characterization of breast-simulating phantoms that are used to evaluate the diagnostic performance of microwave imaging technologies. The second application involves the use of the characterization system for the pre-classification of normal and malignant tissues also as a decision support system for conventional biopsies, enabling real-time tissue characterization. To accomplish this aim, the author conducted experimental research at the Hospital Virgen de la Salud in Toledo, Spain, where biopsy samples from 18 patients were gathered and processed via the microwave characterization system

Progetto, realizzazione e validazione di un sistema di caratterizzazione elettromagnetica dei tessuti biologici basato su una sonda a cavo coassiale aperto.

La misura delle proprietà dielettriche di un materiale è di fondamentale importanza al fine di ottenere le informazioni necessarie per la comprensione dei fenomeni di interazione tra le onde elettromagnetiche ed i tessuti biologici. In questo lavoro di tesi viene dapprima analizzato lo stato dell’arte relativamente ai diversi metodi per la caratterizzazione dei materiali con particolare riferimento ai tessuti biologici. Tra tutti i metodi analizzati la sonda a cavo coassiale aperto è il metodo più idoneo in quanto semplice da utilizzare, non distruttivo e consente di discriminare valori di permittività e conducibilità su un ampio spettro frequenziale. Durante la prima fase del lavoro di tesi è stata realizzata la sonda mediante l’utilizzo di un software di simulazione elettromagnetica. Parallelamente è stato implementato l'algoritmo di inversione basato sul modello della linea di trasmissione virtuale mediante il quale ricavare i parametri dielettrici di interesse. In fase successiva la sonda è stata realizzata fisicamente e testata in laboratorio mediante l’utilizzo di fantocci liquidi appositamente creati

Methodology for the Development of Broadband Multilayer Microwave Absorbers

In this work, a methodology is proposed to optimize the parameters of the multilayer microwave absorber (MMA), such as thickness and selection of materials to obtain the desired reflection coefficient bandwidth (RCBW). The transmission line method is used to compute the absorption bandwidth. The aim is to obtain the broadband MMA operating in the frequency range from 1 to 20 GHz. Consequently, genetic algorithm (GA) is employed to optimize the parameters of MMA. Moreover, the proposed methodology is implemented by using a database of the lossy magnetic and dielectric which are commercially available materials. For an example, two layers of MMA are optimized and computed the desired RCBW, where the level of RC is varied from -5 to -10 dB

Electromagnetically characterized gelatinous-based phantoms for breast microwave imaging

The present work proposes a procedure based on a modified recipe to fabricate electromagnetically characterized phantoms, made of gelatinous-based mixture. As a main advantage we highlight the use of commercially available and very inexpensive gelatin along with the addition of food colorants for the phantom assembly. Furthermore, we have demonstrated that by storing the samples in a refrigerator at a stable temperature of 4°C, the phantoms maintain stable dielectric properties up to 14 days. Their dielectric properties have been measured in the [1-8.5] GHz frequency range using a coaxial probe kit. The promising results demonstrate the potential of the recipe method to realize multistrate breast phantoms representing different tissues

Dielectric Characterization of Breast Biopsied Tissues as Pre-Pathological Aid in Early Cancer Detection: A Blinded Feasibility Study

Dielectric characterization has significant potential in several medical applications, providing valuable insights into the electromagnetic properties of biological tissues for disease diagnosis, treatment planning, and monitoring of therapeutic interventions. This work presents the use of a custom-designed electromagnetic characterization system, based on an open-ended coaxial probe, for discriminating between benign and malignant breast tissues in a clinical setting. The probe’s development involved a well-balanced compromise between physical feasibility and its combined use with a reconstruction algorithm known as the virtual transmission line model (VTLM). Immediately following the biopsy procedure, the dielectric properties of the breast tissues were reconstructed, enabling tissue discrimination based on a rule-of-thumb using the obtained dielectric parameters. A comparative analysis was then performed by analyzing the outcomes of the dielectric investigation with respect to conventional histological results. The experimental procedure took place at Complejo Hospitalario Universitario de Toledo—Hospital Virgen de la Salud, Spain, where excised breast tissues were collected and subsequently analyzed using the dielectric characterization system. A comprehensive statistical evaluation of the probe’s performance was carried out, obtaining a sensitivity, specificity, and accuracy of 81.6%, 61.5%, and 73.4%, respectively, compared to conventional histological assessment, considered as the gold standard in this investigation