Generalized Signal Models and Direct FID-Based Dielectric Parameter Retrieval in MRI

TL;DR

This paper develops comprehensive signal models for MRI that incorporate dielectric properties of objects, enabling the potential retrieval of these properties from measured signals, which enhances the understanding and imaging capabilities in MRI.

Contribution

The paper introduces full-wave signal models for MRI that include dielectric parameters and demonstrates the possibility of retrieving these parameters from FID signals.

Findings

Signal models incorporate dielectric parameters explicitly.

Retrieval of dielectric properties from FID signals is feasible.

Models are validated for small homogeneous objects using quasi-static approximation.

Abstract

In this paper we present full-wave signal models for magnetic and electric field measurements in magnetic resonance imaging (MRI). Our analysis is based on a scattering formalism in which the presence of an object or body is taken into account via an electric scattering source. We show that these signal models can be evaluated, provided the Green's tensors of the background field are known along with the dielectric parameters of the object and the magnetization within the excited part of the object. Furthermore, explicit signal expressions are derived in case of a small homogeneous ball that is embedded in free space and for which the quasi-static Born approximation can be applied. The conductivity and permittivity of the ball appear as explicit parameters in the resulting signal models and allow us to study the sensitivity of the measured signals with respect to these dielectric parameters. Moreover, for free induction decay signals we show that under certain conditions it is possible to retrieve the dielectric parameters of the ball from noise-contaminated induction decay signals that are based on electric or magnetic field measurements.