Distortion‐free, high‐isotropic‐resolution diffusion MRI with gSlider BUDA‐EPI and multicoil dynamic B<sub>0</sub> shimming
Congyu Liao, Berkin Bilgiç, Qiyuan Tian, Jason Stockmann, Xiaozhi Cao, Qiuyun Fan, Siddharth Iyer, Fuyixue Wang, Chanon Ngamsombat, Wei‐Ching Lo, Mary Kate Manhard, Susie Y. Huang, Lawrence L. Wald, Kawin Setsompop
Abstract
Purpose We combine SNR‐efficient acquisition and model‐based reconstruction strategies with newly available hardware instrumentation to achieve distortion‐free in vivo diffusion MRI of the brain at submillimeter‐isotropic resolution with high fidelity and sensitivity on a clinical 3T scanner. Methods We propose blip‐up/down acquisition (BUDA) for multishot EPI using interleaved blip‐up/blip‐down phase encoding and incorporate B 0 forward‐modeling into structured low‐rank reconstruction to enable distortion‐free and navigator‐free diffusion MRI. We further combine BUDA‐EPI with an SNR‐efficient simultaneous multislab acquisition (generalized slice‐dithered enhanced resolution [“gSlider”]), to achieve high‐isotropic‐resolution diffusion MRI. To validate gSlider BUDA‐EPI, whole‐brain diffusion data at 860‐μm and 780‐μm data sets were acquired. Finally, to improve the conditioning and minimize noise penalty in BUDA reconstruction at very high resolutions where B 0 inhomogeneity can have a detrimental effect, the level of B 0 inhomogeneity was reduced by incorporating slab‐by‐slab dynamic shimming with a 32‐channel AC/DC coil into the acquisition. Whole‐brain 600‐μm diffusion data were then acquired with this combined approach of gSlider BUDA‐EPI with dynamic shimming. Results The results of 860‐μm and 780‐μm datasets show high geometry fidelity with gSlider BUDA‐EPI. With dynamic shimming, the BUDA reconstruction’s noise penalty was further alleviated. This enables whole‐brain 600‐μm isotropic resolution diffusion imaging with high image quality. Conclusions The gSlider BUDA‐EPI method enables high‐quality, distortion‐free diffusion imaging across the whole brain at submillimeter resolution, where the use of multicoil dynamic B 0 shimming further improves reconstruction performance, which can be particularly useful at very high resolutions.