Radio-frequency coil design for high-field magnetic resonance imaging

Magnetic resonance imaging (MRI) is a valuable medical diagnostic tool that uses the interaction of strong magnetic fields and atomic nuclei in biological tissues to obtain high-resolution tomographic images of patients. It is also a fast growing research field dominated by functional MRI (fMRI), which allows real-time monitoring of neuronal activity in the brain. The demanding nature of this new research necessitates the move towards higher and higher magnetic field strength to improve image signal-to-noise ratio (SNR).; The MRI radio-frequency (RF) coil is a critical component of an MRI system that excites the nuclei in the sample and receives the signal that is reconstructed into the image. RF coil quality is as important to the image SNR as the primary magnetic field strength. However, designing RF coils for high-field MRI is a difficult challenge, since the older designs do not scale well to higher frequency (which increases linearly with magnetic field strength), and good high-frequency coil modeling tools are not available.; In this project, unconventional RF coil designs and simulation tools are developed with a goal of overcoming the limitations of existing coil technology and modeling methodology. The new modeling tools are based on the multi-conductor transmission (MTL) line theory and the method of lines (MoL). These methods enable high-frequency coil design and optimization without requiring excessive computational resources typical of traditional three-dimensional numerical approaches.; The modeling methods are applied to practical coil design, resulting in the development of the microstrip TEM resonator volume coil concept and the construction of prototype coils. A dual-coil system designed for brain imaging in small rodents at 4.7 T (200 MHz) produced excellent images of the entire brain. A larger volume coil designed for imaging rhesus monkeys at 4.7 T also demonstrated good results.