Comparing parallel transmit 2-spoke against circularly polarized pulses for 7T whole brain diffusion MRI

Diffusion MRI (dMRI) is inherently limited by SNR. 7T scans increase intrinsic SNR but suffer from regions of signal dropout, especially in temporal lobes and cerebellum. We applied dynamic parallel transmit (pTx) to allow whole-brain 7T dMRI and scanned 7 volunteers comparing pTx 2-spoke and circularly polarized pulses. PTx 2-spoke scans increased whole-brain mean temporal SNR increased by 22%, produced cleaner fractional anisotropy maps, and reduced fiber estimation uncertainty by 4% (P=0.016) for first fibers and 2% (P<0.001) for second fibers. However, less restrictive SAR limits will be needed for clinical translation of our approach due to long scan time.