Multi-Slice B1+ Shimming for 7T MRI

Andrew T. Curtis¹, Kyle M. Gilbert¹, Martyn L. Klassen¹, Joseph S. Gati¹, Ravi S. Menon¹

Leveraging multi-channel transmit arrays to produce efficient and uniform RF fields becomes a difficult task as field strength increases, thanks to the well known wave effects, and greater coupling between the coils and the sample, especially in tight-fitting arrays. In this situation, the traditional geometric driving phase configuration fails to produce the expected maximum excitation efficiency. It is demonstrated that utilizing the extra degrees of freedom present in multi-slice imaging protocols allows calculation of B1+ shim solutions that can markedly reduce transmitted power (and consequently global SAR) by shimming to recover efficient excitation modes.