Development of MR-based procedures for the implementation of patient-specific dielectric models for clinical use

The use of medical techniques based on the application of Electro Magnetic Fields (EMF) on the human body is growing significantly, both for therapeutic and diagnostic purposes. In order to provide safe and effective treatments, a clear understanding of the reaction of human tissues to EMF exposure is needed. This information is provided by the tissues’ dielectric properties which must be accurately characterized for the patients undergoing EMF-based techniques. Due to the heterogeneity and the complexity of biological tissues, these properties can relevantly change from subject to subject and depend on many factors. For this reason, there is the need to characterize the dielectric properties of each patient specifically and in the frequency range of application of the main EMF-based medical techniques, i.e., from tens of MHz to tens of GHz.This work, presenting the state of the art of the traditional dielectric spectroscopy techniques, highlights the main limits affecting the current methodologies. Since traditional techniques are mainly invasive and provide single frequency results, they cannot be adopted to determine the dielectric properties of biological tissues in in vivo conditions and in a wideband frequency range. In this work a Magnetic Resonance Imaging (MRI)-based approach for a non-invasive and wideband (10 MHz – 20 GHz) dielectric characterization of biological tissues of the pelvic region is proposed. The approach relies on a model based on two terms related to two MRI derivable quantities, i.e., the water content of biological tissues and their dielectric properties obtained through the Electric properties Tomography (EPT) approach at the frequency of the MR scanner. First, the model is validated theoretically using data from the literature. Secondly, measurements conducted on ex-vivo animal samples, both with traditional techniques and MRI, are used for the experimental validation of the model. The ability of the proposed approach to reconstruct the dielectric properties of biological tissues from MRI in the frequency range of interest is proved,presenting a non-invasive and wideband methodology applicable in vivo, overcoming the limits of the currently adopted approaches.