Human Brain Imaging at 9.4 Tesla Using a Combination of Traveling Wave Excitation with a 15-channel Receive-only Array

Introduction The combination of a circularly polarized (CP) volume coil for spin excitation with a multi-channel receive-only array is a successful setup for routine human brain imaging at 7 Tesla. For reception, the use of multiple surface coils is important for a high SNR and for the utilization of parallel imaging techniques. For transmission, the main strength of the CP coil is the reasonable B1 homogeneity over a large FOV in unison with simple usage, which is in contrast with more sophisticated static or tailored RF shimming techniques using multichannel transmit coils. At 9.4 Tesla, however, the even shorter RF wavelength in tissue causes the B1 field to be unacceptably inhomogeneous, especially in the ventral parts of the brain. In addition, the field-of-view of coils that are based on half-lambda resonators further decreases. Therefore, a substitute for the CP coil with a more uniform B1 field pattern over a large FOV is desirable. Traveling wave imaging [1] using a Tx/Rx patch antenna has the potential to provide a more homogeneous spin excitation over larger regions [2, 3], but in turn suffers from poor sensitivity. Therefore, we tested the combination of traveling wave excitation with a 15-channel receive-only array and show initial results utilizing this setup for human brain imaging at 9.4 Tesla.