Analysis of B1 field profiles and SAR values for multi-strut transverse electromagnetic RF coils in high field MRI applications.

In this work, the B1 field homogeneity and specific absorption rate (SAR) values were evaluated for three high-frequency (340 MHz) radio frequency coils designed for use in human magnetic resonance imaging at 8 tesla. Eight-, 16-, and 24-strut transverse electromagnetic (TEM) resonators were examined both experimentally and with the finite difference time domain numerical method. It was observed that increasing the number of TEM elements acted to lower the maximal achievable frequency of the coil and to increase the experimental complexities associated with tuning and matching. In addition, it is demonstrated from experiment and numerical analysis that the circularly polarized component of the B1 (B1+) field homogeneity in the head improved most from 8- to 16-strut coils. Numerical analysis revealed little difference in terms of SAR distribution between these coils; however, stronger tissue/coil coupling and consequently higher SAR peak values were obtained for the 8-strut case.