Advancing RF coil technology for human brain magnetic resonance imaging at ultrahigh field

Abstract

The demand for higher signal-to-noise ratio (SNR) of magnetic resonance (MR) imaging (MRI) led to the development of ultrahigh field (UHF) MRI. UHF technology enables MRI and magnetic resonance spectroscopic imaging (MRSI) with higher spatiotemporal and spectral resolutions and better contrast, opening new opportunities for studying human brain structure and function, cerebral metabolism and neuroenergetics. However, there are technological challenges such as inhomogeneous imaging distribution due to wave behavior at UHF. Various RF engineering approaches have been used to improve MR imaging quality by enhancing the RF coil magnetic fields (B1) and imaging SNR. High permittivity material (HPM) technology provides an effective method to enhance the RF transmission (B1+) and reception (B1-) magnetic field strength, thereby achieving higher imaging SNR at different field strengths. This thesis developed and evaluated RF head array coils integrated with HPM of different forms and relative permittivity values, aiming to significantly improve the strengths and spatial distribution of the RF coil B1 field, as well as the SNR and quality of various human brain imaging applications from proton (1H) MRI at 7 Tesla (T) to low-gamma X-nuclear deuterium (2H) and oxygen-17 (17O) MRSI at UHF of greater than or equal to 7T. Significant B1 and SNR improvements were achieved for 1H MRI (>80% increase in SNR) and 2H or 17O MRSI (>40% increase in B1+, B1- and SNR) at UHF. These technological advances have significantly enhanced the capabilities of MRI/MRSI for brain research and potential clinical translation at 7T and beyond.