Thesis title: 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 several 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 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 MRI 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.