Highly‐accelerated Bloch‐Siegert mapping using joint autocalibrated parallel image reconstruction

Purpose To reconstruct accurate single- and multichannel Bloch-Siegert transmit radiofrequency ([Formulaomitted]) field maps from highly accelerated data. Theory and Methods The approach is based on the fact that the [Formulaomitted]-to-phase encoding pulse for each transmit coil and off-resonance frequency applies a unique phase shift to the same underlying image. This enables joint reconstruction of all images in a Bloch-Siegert acquisition from an augmented set of virtual receive coils, using any autocalibrated parallel imaging reconstruction method. Results Simulations with an eight channel transmit/receive array head coil at 7T show that accurate [Formulaomitted] maps can be produced at acceleration factors of 16 and 6 for Cartesian and spiral sampling, respectively. A phantom experiment with a six channel transverse electromagnetic (TEM) transceive array coil allowed accurate reconstruction at 16 acceleration. 7T in vivo experiments performed using 32 channel receive and two-channel transmit coils further demonstrate the proposed method's ability to produce high-quality [Formulaomitted] maps at accelerations of 32 and 8 for Cartesian and spiral trajectories, respectively. Reconstruction accuracy is improved using disjoint k-space sampling patterns between acquisitions. Conclusion The proposed approach allows high acceleration factors in Bloch-Siegert [Formulaomitted] mapping and can significantly reduce the scan time requirements for mapping the [Formulaomitted] fields of transmit arrays. Magn Reson Med 71:1470-1477, 2014. copyright 2013 Wiley Periodicals, Inc.