Romer‐ EPTI : Rotating‐view motion‐robust super‐resolution EPTI for SNR ‐efficient distortion‐free in‐vivo mesoscale

Abstract Purpose To overcome the major challenges in diffusion MRI (dMRI) acquisition, including limited SNR, distortion/blurring, and susceptibility to motion artifacts. Theory and Methods A novel Romer‐EPTI technique is developed to achieve SNR‐efficient acquisition while providing distortion‐free imaging, minimal spatial blurring, high motion robustness, and simultaneous multi‐TE imaging. It introduces a ROtating‐view Motion‐robust supEr‐Resolution technique (Romer) combined with a distortion/blurring‐free Echo Planar Time‐resolved Imaging (EPTI) readout. Romer enhances SNR through simultaneous multi‐thick‐slice acquisition with rotating‐view encoding, while providing high motion‐robustness via a high‐fidelity, motion‐aware super‐resolution reconstruction. Instead of EPI, the in‐plane encoding is performed using EPTI readout to prevent geometric distortion, T 2 / T 2 *‐blurring, and importantly, dynamic distortions that could introduce additional blurring/artifacts after super‐resolution reconstruction due to combining volumes with inconsistent geometries. This further improves effective spatial resolution and motion robustness. Additional developments include strategies to address slab‐boundary artifacts, achieve minimized TE and optimized readout for additional SNR gain, and increase robustness to strong phase variations at high b ‐values. Results Using Romer‐EPTI, we demonstrated distortion‐free whole‐brain mesoscale in‐vivo dMRI at both 3T (500‐μm isotropic [iso] resolution) and 7T (485‐μm iso resolution) for the first time. Motion experiments demonstrated the technique's motion robustness and its ability to obtain high‐resolution diffusion images in the presence of subject motion. Romer‐EPTI also demonstrated high SNR gain and robustness in high b ‐value ( b  = 5000 s/mm 2 ) and time‐dependent dMRI. Conclusion The high SNR efficiency, improved image quality, and motion robustness of Romer‐EPTI make it a highly efficient acquisition for high‐resolution dMRI and microstructure imaging.