Extraction of electrical properties of strokes from magnetic resonance scans — Testing on simplified head phantoms

Abstract

Several studies have reported considerable differences in dielectric properties between healthy and pathological tissues. In addition, in the area of electromagnetic field applications in medicine, discussions about the correctness of dielectric properties of biological tissues measured ex vivo (the most common method of measurement), for example due to lower blood content, are taking place. By using the inherent electromagnetic working principle of magnetic resonance (MR) systems, changes in wave propagation can be used to extract values of dielectric properties of target tissues from MR images. This method thus represents a method for noninvasive measurement of dielectric properties of biological tissues in Vivo. The results might be used for detection and classification of illness. It has been show in literature that both magnitude and phase of the MR RF waves can be determined using standard MR imaging sequences. By using the resulting magnitude and phase of RF waves dielectric properties can be determined by simply using the Helmholtz equation. In this study we confirm such reports through numerical simulations using high-resolution anatomical head model and a model of bird-cage coil. Furthermore, a simplified head phantom mimicking dielectric properties of strokes and brain tissues was designed and manufactured and information from real MR scans was processed. As it will be shown in this work, this process works well for data obtained via numerical simulations but it is not as straightforward, for the images coming from the MR system. There, additional processing in order to compensate for the presence of noise and de-phasing is crucial.