Z-Shim RF Coil Design Enhances Parallel Transmit Performance in Body Imaging at 3T

Xiaoping Wu¹, Jinfeng Tian¹, Sebastian Schmitter¹, Brian Hanna¹, Joseph Pfeuffer², Michael Hamm², Juergen Nistler², University of Minnesota University of Minnesota Vaughan¹, Kamil Ugurbil¹, Pierre-Francois Van de Moortele¹

There has been an increasing interest in designing RF arrays with coil elements distributed in all three dimensions so as to also allow B1+ manipulation along the Z direction. Such Z-shim coils have been shown to provide improved RF transmit efficiency for brain imaging, as compared to a conventional coil which has only in-plane encoding capability. In this study, we evaluate the performance of a Z-shim RF array designed for body imaging at 3T and compare it to a conventional array, by designing parallel transmit (pTX) RF pulses with power and SAR regularizations based on electromagnetic simulations of the two coils. Our results show that the Z-shim RF array can give rise to large improvement of flip angle homogenization and/or reduction of SAR for pTX when used for body imaging at 3T, as compared to the conventional coil without Z-encoding capability.