Romer-EPTI: rotating-view motion-robust super-resolution EPTI for SNR-efficient distortion-free in-vivo mesoscale dMRI and microstructure imaging

Abstract

PurposeTo overcome the major challenges in diffusion MRI acquisition, including low SNR, distortion/blurring, and motion vulnerability.MethodsA novel Romer-EPTI technique is developed to provide high SNR, sharp spatial resolution, high motion-robustness, images free from distortion and slab-boundary artifacts, and simultaneous multi-TE imaging. It integrates a ROtating-view Motion-robust supEr-Resolution technique (Romer) with a distortion/blurring-free self-navigated EPTI encoding. Romer enhances SNR with high-motion robustness by employing a thick-slice acquisition with rotating-view encoding, and a motion-aware super-resolution reconstruction that incorporates motion, slice-profile and real-value diffusion. The in-plane encoding of the thick-slice volumes is performed using distortion/blurring-free EPTI readout, which further improves Romer’s motion robustness by preventing detrimental blurring resulting from combination of inconsistent geometries caused by motion or eddy-current induced dynamic distortions. The Romer encoding, motion-aware reconstruction, together with T2/T2*-blurring-free EPTI readout enable effective reconstruction of the sharp spatial resolution. Furthermore, Romer-EPTI provides short TE and low SAR for 7T dMRI and high robustness to phase variations for high-b-value imaging.ResultsUsing Romer-EPTI, we demonstrate distortion-free whole-brain mesoscale in-vivo dMRI at both 3T (500μm-iso) and 7T (485μm-iso) for the first time, with high SNR efficiency (e.g., √25×), and high image quality free from distortion and slab-boundary artifacts with minimal blurring. Motion experiments demonstrate the high motion-robustness of Romer-EPTI and its ability to recover sharp images in presence of subject motion. We also demonstrate its significant SNR gain and robustness in high b-value (b=5000s/mm2) and time-dependent dMRI.ConclusionRomer-EPTI significantly improves SNR, motion-robustness, and image quality of dMRI, providing a highly efficient acquisition for high-resolution dMRI and microstructure imaging.