Distortion‐free, high‐isotropic‐resolution diffusion MRI with gSlider BUDA‐EPI and multicoil dynamic B₀ shimming

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

SNR-efficient distortion-free diffusion relaxometry imaging using ACcelerated Echo-train shifted EPTI (ACE-EPTI)

“…To provide shorter TRs and higher SNR-efficiency for whole-brain imaging, SMS acquisition has been integrated into the ACE-EPTI, and shown consistent high-quality results. To further improve the efficiency for a high isotropic resolution acquisition, simultaneous multi-slab acquisition such as gSlider (53)(54)(55) can also be combined with ACE-EPTI in the future. Additionally, ACE-EPTI can be also applied to other imaging applications outside of dMRI, such as multi-echo fMRI (56,57) and T2 * mapping that has been previously studied using EPTI (28,58), with effective correction of shot-to-shot variation and a higher temporal resolution.…”

Recent Advances in Radio‐Frequency Coil Technologies: Flexible, Wireless, and Integrated Coil Arrays

“…Additionally, the low inductance of the coil elements allows the DC currents to be quickly updated to dynamically shim individual slices in a multi-slice acquisition (or groups of slices in a multi-band acquisition), resulting in a more effective shimming than global (eg, whole-brain) shimming. 73,87,88 One potential limitation of integrated RF/shim coil arrays is that the coil geometry (i.e., number, size, shape, and location of the coil elements) may not always be optimal to achieve both a high RF and shimming performance. For example, the coil elements of a body coil array, which are typically larger than those of a head coil array, may not be sufficiently small to shim the localized B 0 inhomogeneities in the abdomen.…”

“…84 In the dual-stream iPRES-W coil design, two iPRES-W coil elements (along with additional iPRES coil elements) are used to enable two concurrent wireless applications, such as wireless localized B 0 shimming and wireless respiratory monitoring with a respiratory belt. 71 While still relatively recent, integrated RF/shim coil arrays have already been used to shim localized B 0 inhomogeneities in multiple applications in the human brain, 71,73,78,79,[85][86][87][88]93 abdomen, 82,89,90 spinal cord, 84,94,95 and breast, 83 as well as the monkey brain 96 and rat brain. 97 Specifically, they have been used: to correct for geometric distortions in EPI (Fig.…”

Efficient T2 mapping with blip‐up/down EPI and gSlider‐SMS (T2‐BUDA‐gSlider)

“…However, because the hybrid-space SENSE requires explicit knowledge of phase variations between the blip-up and -down shots, their inaccurate estimation may introduce reconstruction artifacts and noise amplification. 33 In this work, we propose to combine gSlider encoding and blip-up/down acquisition (BUDA) 34 to achieve highresolution and distortion-free T 2 mapping with whole-brain coverage. First, we incorporate Hankel structured lowrank constraint into our BUDA reconstruction to recover distortion-free images from blip-up/down shots without navigation.…”

“…In this work, we propose to combine gSlider encoding and blip‐up/down acquisition (BUDA) 34 to achieve high‐resolution and distortion‐free T 2 mapping with whole‐brain coverage. First, we incorporate Hankel structured low‐rank constraint into our BUDA reconstruction to recover distortion‐free images from blip‐up/down shots without navigation.…”