Application of finite-difference time-domain method in RF problems associated with magnetic resonance imaging

摘要

Magnetic resonance imaging (MRI) has been widely applied in medical diagnostics and other fields. It operates at field strengths ranging from a small fraction of a Tesla to as much as four Tesla, with some investigators discussing even higher fields. Unfortunately, RF field penetration effects are magnified at higher fields, potentially affecting image contrast and RF power deposition. Thus, it is important to know the RF field distribution inside the imaging samples with a high degree of accuracy to ensure patient safety and diagnostic quality. Currently, there are various analytical and numerical methods for calculating the RF fields. However, these methods typically do not account for arbitrary, inhomogeneous samples, and most use narrow-band frequency analysis. The finite difference time domain (FDTD) method has been proposed in this dissertation as an approach to overcoming these limitations. The advantage of the FDTD method in RF problem analysis is that the RF coils and inhomogeneous samples can be generally modeled in the computer code and one computation will lead to wide-band frequency response.;Based on the study of nuclear magnetic resonance (NMR) phenomenon and various numerical methods used in MRI, this dissertation has developed and verified the FDTD method applied to the NMR environment. Direct laboratory measurement of RF characteristics and MR imaging experiments are performed to evaluate the capability of the FDTD method in MRI applications. Finally, this method is utilized to perform RF coil analysis, design and MR imaging simulations. Several RF problems are investigated in detail, which include RF field homogeneity, RF shielding effects, and signal-to-noise ratio (SNR).