FIELD INHOMOGENEITY COMPENSATION IN HIGH FIELD MAGNETIC RESONANCE IMAGING (MRI) by

FIELD INHOMOGENEITY COMPENSATION IN HIGH FIELD MAGNETIC RESONANCE IMAGING (MRI) Zhenghui Zhang, PhD University of Pittsburgh, 2006 This thesis concentrates on the reduction of field (both main field B0 and RF field B1) inhomogeneity in MRI, especially at high B0 field. B0 and B1 field inhomogeneity are major hindrances in high B0 field MRI applications. B1 inhomogeneity will lead to spatially varying signal intensity in the MR images. B0 inhomogeneity produces blurring, distortion and signal loss at tissue interfaces. B0 artifacts are usually termed off-resonance or susceptibility artifacts. None of the existing methods can perfectly correct these inhomogeneity artifacts. This thesis aims at developing three-dimensional (3D) tailored RF (TRF) pulses to mitigate these artifacts. A current limitation in the use of 3D TRF techniques, however, is that pulses are often too long for practical clinical applications. Multiple transmission techniques are proposed to decrease pulse lengths and provide an inherent correction for B1 inhomogeneity. Shorter pulses are also more robust to profile distortions from susceptibility effects. Specifically, slice-selective 3D TRF pulses for multiple (or “parallel”) transmitters were designed and validated in uniform phantom and human brain experiments at 3 Tesla. A pseudotransmit sensitivity encoding (“transmit SENSE”) method was introduced using a body coil