Application of Parallel Transmission to Ultra-High Field Magnetic Resonance Spectroscopy and Imaging

Abstract

Magnetic resonance imaging is a non-invasive imaging technology that produces detailed images of biological tissue with anatomical and functional information. While the use of ultra-high field helps improve the sensitivity of MRI, one major challenge of imaging at such extreme field strength is the transmit B1 field inhomogeneity. The technique of parallel transmission has been proposed to mitigate such challenge and provides opportunities to explore new acquisition methods. To take advantage of these capabilities, this thesis investigates its application to spectroscopy and imaging at ultra-high field consisting of the following three projects. First, a novel spectroscopy acquisition method is proposed featuring the use of a parallel transmit optimized 3D adiabatic spectral-spatial pulse, where multiple improvements including reduced heating and increased robustness against field imperfections are demonstrated by phantom and in-vivo brain studies at 7T. Second, the use of a variety of radiofrequency management methods with parallel transmission is explored in the human torso for the first time at 10.5T. Preliminary high quality images of multiple anatomies including multi-parametric mappings in the prostate are presented. Last, a novel non-localized efficiency RF shimming is proposed and extended to Acquisition Modes Optimized for Refocused Echoes (AMORE), a novel strategy to design modes in Time Interleaved Acquisition of Modes (TIAMO). Both approaches are optimized for the clinically relevant turbo spin echo imaging while also benefiting other acquisitions. Improvements are demonstrated in vivo and evidenced by a higher transmit efficiency with reduced non-uniformity or signal dropout in multiple targets including brain, knee, and pelvis.