Effects of increasing RF transmit frequency on SAR and SAR efficiency in MRI up to 14 Tesla

Motivation: With human MRI systems reaching 11.7T and a 14T system underway, investigating transmit performance and safety at UHF is essential. Goal(s): To evaluate effects of increasing RF transmit frequency on SAR and SAR efficiency in the UHF regime. Approach: A simplified model of a linearly polarized plane wave in media with varying material parameters was used to interpret the frequency dependence of SAR and SAR efficiency. Findings were evaluated in a more realistic model of an 8-channel dipole head array at UHF. Results: The findings support and elucidate the less-than-linear increase in SAR with rising RF frequency, contrasting with the expected quadratic rise. Impact: This study investigates the effects of increasing RF frequencies on SAR and SAR efficiency, enhancing the understanding of the underlying causalities. Findings indicate the feasibility of safely operating MRI systems up to 14T, supporting ongoing advancements in UHF MRI technology.