Induced current magnetic resonance electrical impedance tomography (ICMREIT) with low frequency switching of gradient fields

---

Tezin Türü: Doktora

Tezin Yürütüldüğü Kurum: Orta Doğu Teknik Üniversitesi, Mühendislik Fakültesi, Elektrik ve Elektronik Mühendisliği Bölümü, Türkiye

Tezin Onay Tarihi: 2017

Öğrenci: HASAN HÜSEYİN EROĞLU

Danışman: BEHÇET MURAT EYÜBOĞLU

Özet:

In this thesis, it is aimed to investigate induced current magnetic resonance electrical impedance tomography (ICMREIT) starting from modeling and analysis to experimental validation. Forward and inverse problems of ICMREIT are formulated. A magnetic resonance imaging (MRI) pulse sequence is proposed for the realization of ICMREIT using the slice selection (z) gradient coil of MRI scanners. Considering the proposed MRI pulse sequence, relationship between the low frequency (LF) MR phase and the secondary magnetic field is expressed. Forward problem is solved using finite element method (FEM) for z and y gradient coils of MRI scanners. For the solution of the inverse problem, J-derivative and E-calculation image reconstruction algorithms are proposed and the performance of the algorithms is evaluated by using simulated measurements. Sensitivity and distinguishability analyses are performed in order to investigate imaging characteristics of ICMREIT. Phantom experiments are performed for physical realization of ICMREIT. Simulated and physical LF phase measurements have similar characteristics. Low sensitivity of LF phase measurements is thought to be the main reason for the quantitative difference between the simulated and experimental measurements and the major limitation of the method towards clinical applications. Using the LF phase measurements, current density and true conductivity images are reconstructed. Reconstructed current density and conductivity images show that ICMREIT is a safe and a potentially applicable medical imaging method. Reconstructed conductivity images are rough estimates of the simple phantoms and they exhibit qualitative reconstructions rather than quantitative images. Sensitivity of LF phase measurements and image reconstruction performance should be increased in order to use the method in clinical practice.