From brain to body: advancing human MR(S)I at 7 tesla

Magnetic resonance (MR) at “ultra-high field” (UHF, magnetic field strength ≥ 7 tesla) benefits from an increase in signal-to-noise ratio and spectral resolution. However, many new challenges arise when transitioning to 7 tesla and beyond, which must be addressed before one can reap the rewards of UHF MR. It is therefore no surprise that the revolution of human UHF MR was led mainly by applications in the brain and extremities: superficial, relatively small body parts, largely free of respiratory and cardiac motion. In this thesis, we further advanced human 7-tesla MR from many angles, moving from brain to body: we translated existing techniques to UHF, and developed new ones, while addressing many UHF-specific challenges. In chapter 3, a compressed sensing (CS)-accelerated protocol was developed to investigate cerebrospinal fluid clearance, and its temporal dependence on various physiological forces, throughout the entire brain. In chapter 4, we investigated to what extent CS could offer additional acceleration in a clinical wrist protocol, and showed how through-slice water-fat shift artifacts could be addressed. In chapter 5, we moved towards the liver, and showed that RF-transmission (B1+) inhomogeneity can be reduced when combining parallel transmission with an appropriate B1+ mapping technique. Chapter 6 builds further upon chapter 5, where we showed the increased spatial resolution that can be achieved by moving to a CS-accelerated free-breathing acquisition. Finally, in chapter 7 we showed the technical feasibility of full-liver phosphorus (31P) MR spectroscopic imaging, and the potential thereof for treatment response evaluation in patients with hepatic metastases.