Development of a Multichannel Transmit Array for Knee Arterial Spin Labeling Imaging at 7 Tesla

Motivation: To overcome the limitations of a commercially-available single-transmit channel knee coil in terms of B1+ inhomogeneity in the imaging region, and limited coverage in the proximal femoral meta-diaphysis for knee bone marrow arterial spin labeling (ASL) at 7T. Goal(s): Our goal was to evaluate the B1+ performance of possible transmit array designs, as the first step towards an optimized design for an ASL imaging knee coil. Approach: 6- and 8-channel multichannel transmit array designs were explored experimentally and in simulation. Results: Both evaluated transmit arrays provided more uniform B1+ and better coverage in the labelling region compared to a single-transmit channel knee coil. Impact: Development of pTx-capable knee coils will greatly improve the quality, reliability, and efficiency of knee ASL imaging at 7T and can provide the clinically critical but currently not available platform for the assessment of knee bone marrow perfusion.