Scalable fast online-customized (FOCUS) pTx pulses for 3D TSE sequences at 7T

Motivation: 3D TSE sequences at 7T suffer from poor homogeneity, signal dropouts and local SAR limits. Goal(s): Clinically acceptable image quality using scalable dynamic parallel transmit (pTx) pulses under SAR-constraintsApproach: Prior to the scan, a dictionary of preoptimized, symmetric pTx pulses is built. At the scanner, the best pulse for that subject is identified and serves as initialization for a then fast individual optimization constrained to maximum SAR, maximum voltage and temporal symmetry. Results: Clinically acceptable image homogeneity is achieved with two different pulses at the expense of 0.4ms/0.9ms longer pulse duration and 220%/14% higher SAR than the commonly used 1Tx pulse. Impact: A workflow to design customized and arbitrarily scalable pTx pulses is demonstrated, enabling homogeneous 3D TSE imaging of the head with variable flip angles at 7T. Various flip angle trains can be applied as flexibly as on 1Tx systems.