On the Reduction of the Transmit B1 Non-Uniformity and SAR Using a Single-Element Rotating RF Coil

Feng Liu¹, Ewald Weber¹, Adnan Trakic¹, Hua Wang¹, Stuart Crozier¹

In this work, we presented a complete technological solution for tailoring uniform RF fields and minimizing tissue heating for high field MRI. The success of the new B1 shimming technique is largely facilitated by a mechanically rotating RF coil (RRFC) configuration. The proposed method is explained with a biologically loaded, one-element rotating coil operating at 400 MHz. The coil is modelled using the method of moment (MoM) and tissue-equivalent sphere phantom is loaded and modelled using the Greens function method. A sensitivity matrix is constructed based on the pre-characterized B1 and electric field profiles of a large number of angular positions around the imaged phantom, an optimization procedure is then employed for the determination of optimal driving configuration by solving the ill-posed linear system equation. Test simulations show that, compared with conventional bird-cage mode driving scheme, the proposed excitation scheme is capable of significant improvement of the B1 -field homogeneity and reduction of the local and global SAR values. This primary study indicates that the proposed RF excitation technology can effectively perform field-tailoring and might hold the potential of solving the high frequency RF problem.