Fast and accurate multi‐channel mapping based on the TIAMO technique for 7T UHF body MRI

Purpose Current methods for mitigation of transmit field inhomogeneities at ultrahigh field (UHF) MRI by multi‐channel radiofrequency (RF) shimming rely on accurate mapping. This can be time consuming when many RF channels have to be mapped for in vivo body MRI, where the B 1 maps should ideally be acquired within a single breath‐hold. Therefore, a new mapping technique (B1TIAMO) is proposed. Methods The performance of this technique is validated against an established method (DREAM) in phantom measurements for a cylindrical head phantom with an 8‐channel transmit/receive (Tx/Rx) array. Furthermore, measurements for a 32‐channel Tx/Rx remote array are conducted in a large body phantom and the map reliability is validated against simulations of the transmit RF field distribution. Finally, in vivo results of this new mapping technique for human abdomen are presented. Results For the head phantom (8‐channel Tx/Rx coil), the single comparison between B 1 TIAMO, the direct DREAM measurements, and simulation data showed good agreement with 10–19% difference. For the large body phantom (32‐channel Tx/Rx coil), B1TIAMO matched the RF field simulations well. Conclusion The results demonstrate the potential to acquire 32 accurate single‐channel maps for large field‐of‐view body imaging within only a single breath‐hold of 16 s at 7T UHF MRI. Magn Reson Med 79:2652–2664, 2018.