Multichannel and phase based magnetic resonance electrical properties tomography

Abstract

Imaging of electrical properties (EPs, i.e. conductivity and dielectric permittivity) of tissues give valuable information about the physiological and pathological conditions of tissues. Among the EP imaging modalities, magnetic resonance electrical properties tomography (MREPT) has the potential that it can be used both in clinical diagnosis and local specific absorption rate (SAR) calculation. However, there are several issues in the conventional MREPT methods such as boundary artifact, low convective field (LCF) artifact, transceive phase assumption (TPA), usability of only birdcage coil, which precludes the clinical applicability of these methods. This dissertation aims that MREPT can be used in the clinical applications in a fast and reliable way by solving these issues in the conventional MREPT methods. For this purpose two novel methods have been proposed. One is the receive sensitivity (Bequation (PDE) is in the form of convection-reaction equation the coeffcients of which are the derivatives of the measured MR transceive phase. Since only MR phase is used, the method is considerably fast (no B1 mapping is required), and it is applicable for any coil configuration (no TPA is used). The superiority of the proposed method over the conventional phase based EPT method has been shown both in the simple phantom simulations and experiments and in the noisy human brain simulation and healthy volunteer experiments. Furthermore, initial clinical trials with two patients with neurovascular diseases in the subacute phase have been conducted. Each examination took about six minutes. It has been observed that the conductivity increases in the ischemic region when compared to other regions, whereas no conductivity change has been observed in the hematoma region. To standardize the method for the specific clinical applications such as differentiation of the ischemic stroke from the hemorrhagic stroke in the acute phase, further case studies need to be conducted in a systematic way.