Low field MRI RF coils and SNR improvement

Abstract

This thesis investigates RF coil–related challenges in Halbach-based low-field point-of-care MRI systems. It focuses on safety, electromagnetic interference suppression, intrinsic SNR optimization, and the feasibility of fluorine-19 imaging. Chapter 2 evaluates SAR for common low-field RF coil geometries using CST simulations and experimental validation, showing that SAR is generally far below safety limits, except for very short high-power RF pulses. Chapter 3 introduces a simple EMI suppression method using the two-channel structure of a birdcage RF coil, where one channel receives MRI signal plus EMI and the other primarily receives EMI. Combining these channels with a 180° phase shift achieved up to 97% EMI reduction without additional sensors or shielding. Chapter 4 investigates the trade-off between magnet bore diameter, shield spacing, RF transmit efficiency, and B₀ field strength. Simulations and measurements identified an optimal configuration around a 310 mm shield diameter and 320 mm magnet bore diameter for maximum SNR. Chapter 5 demonstrates the feasibility of ¹⁹F MRI at 50 mT using PFOB and a double-tuned ¹H/¹⁹F solenoid coil, showing reduced chemical-shift artifacts and improved acquisition efficiency.