Çok kanallı ve faz temelli manyetik rezonans elektriksel özellik tomografisi

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 (B_1^-) based multichannel cr-MREPT method in which the multi-channel receive coil configuration has been employed to solve the LCF artifact issue in the conventional cr-MREPT method. In addition to this contribution, the method removes the limitation of using birdcage coil in the conventional MREPT methods by enabling the use of standard MRI coils. Since the governing equation is based on the receive sensitivities, a new approach based on two consecutive experiments has been proposed to map the complex B_1^- of each channel. It has been shown in both simulations and experiments that the LCF region differs from one channel to another and artifact-free EP reconstruction is possible by combining the appropriate channels in a logical manner. The drawback of this method is that it is using transceive phase assumption. The second method, in which this drawback and also the issues in the conventional MREPT methods aforementioned above have been solved, is the generalized phase based electrical conductivity imaging method. Starting from the Maxwell's equations and also including EP gradient terms in the formulation, a new equation for the phase-based EPT method has been developed. The governing partial differential equation (PDE) is in the form of convection-reaction equation the coefficients of which are the derivatives of the measured MR transceive phase. Since only MR phase is used, the method is considerably fast (no B_1 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.