Romer‐ EPTI : Rotating‐view motion‐robust super‐resolution EPTI for SNR ‐efficient distortion‐free in‐vivo mesoscale diffusion MRI and microstructure imaging

• Published in: Magnetic resonance in medicine Vol. 93; no. 4; pp. 1535 - 1555
• Main Authors: Dong, Zijing, Reese, Timothy G., Lee, Hong‐Hsi, Huang, Susie Y., Polimeni, Jonathan R., Wald, Lawrence L., Wang, Fuyixue
• Format: Journal Article
• Language: English
• Published: United States Wiley Subscription Services, Inc 01.04.2025; John Wiley and Sons Inc
• Subjects: Algorithms; Blurring; Brain - diagnostic imaging; Coding; Diffusion Magnetic Resonance Imaging - methods; Distortion; Echo-Planar Imaging - methods; Humans; Image acquisition; Image Processing, Computer-Assisted - methods; Image quality; Image reconstruction; Imaging Methodology; Magnetic resonance imaging; Medical imaging; Mesoscale phenomena; Microstructure; Motion; Neuroimaging; Phantoms, Imaging; Phase variations; Robustness; Rotation; Signal-To-Noise Ratio; Spatial discrimination; Spatial resolution; Time dependence; EPTI; super‐resolution; microstructure; diffusion imaging; mesoscale; high resolution
• ISSN: 0740-3194; 1522-2594; 1522-2594
• DOI: 10.1002/mrm.30365

To overcome the major challenges in diffusion MRI (dMRI) acquisition, including limited SNR, distortion/blurring, and susceptibility to motion artifacts. 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 /T *-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. 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 ) and time-dependent dMRI. 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.