Age dependence of brain T1rho and liver intravoxel incoherent motion (IVIM) magnetic resonance imaging

M.Phil. ; T1rho relaxation is the spin-lattice relaxation time constant in the rotating frame in MRI. It represents the decay of transverse magnetization in the presence of a spin-lock radio-frequency field. T1rho is sensitive to low-frequency and static motional processes such as macromolecular composition and proton exchange in tissues, which enable the detection of biochemical changes in tissues. T1rho has been reported to provide early imaging biomarkers for neurodegeneration diseases (e.g., Parkinson’s disease, Alzheimer’s disease, and dementia). However, the relationship between T1rho and physiological brain aging remains unclear. ; Intravoxel incoherent motion (IVIM) is a method to quantitatively assess the microscopic motion of water and the microcirculation of blood that occur in voxels on magnetic resonance (MR) images. It can separate and quantify the perfusion effects from diffusion effects observed from diffusion weighted image (DWI). Recently, there are increasing interests of using IVIM technique to study diffused liver diseases, detect liver tumor and evaluate treatment response. Nevertheless, IVIM is suffering from limited measurement accuracy and reproducibility. In addition, there are still debates about the optimal acquisition and actual value of IVIM parameters. ; The objectives of this thesis are to evaluate the age dependency of human brain t1rho, review reported liver IVIM parameters and explore the application of IVIM in liver fibrosis evaluation with a proposed 3D model. For human brain T1rho, 1.5T MRI scan was performed on 42 healthy volunteers, then the T1rho images of volunteers’ brains were segmented to global tissue structure and specific region of interest (ROI) by using unified segmentation and atlas-based segmentation, respectively. T1rho value was calculated by fitting the mean value of ROI to mono-exponential model. The relationship between age and T1rho value of different ROIs was then evaluated. For liver IVIM, a meta-analysis study was performed to review reported liver ...