In vivo human head MRI at 10.5T: A radiofrequency safety study and preliminary imaging results

Abstract

Purpose: The purpose of this study is to safely acquire the first human head images at 10.5T.

Methods: To ensure safety of subjects, we validated the electromagnetic simulation model of our coil. We obtained quantitative agreement between simulated and experimental $B_1^{+}$ and specific absorption rate (SAR). Using the validated coil model, we calculated radiofrequency power levels to safely image human subjects. We conducted all experiments and imaging sessions in a controlled radiofrequency safety lab and the whole-body 10.5T scanner in the Center for Magnetic Resonance Research.

Results: Quantitative agreement between the simulated and experimental results was obtained including S-parameters, $B_1^{+}$ maps, and SAR. We calculated peak 10 g average SAR using 4 different realistic human body models for a quadrature excitation and demonstrated that the peak 10 g SAR variation between subjects was less than 30%. We calculated safe power limits based on this set and used those limits to acquire T₂ - and $T_2^{\ast }$ -weighted images of human subjects at 10.5T.

Conclusions: In this study, we acquired the first in vivo human head images at 10.5T using an 8-channel transmit/receive coil. We implemented and expanded a previously proposed workflow to validate the electromagnetic simulation model of the 8-channel transmit/receive coil. Using the validated coil model, we calculated radiofrequency power levels to safely image human subjects.

Keywords: 10.5T; MRI; head imaging; radiofrequency safety; ultra-high field.