Single‐shot echo planar time‐resolved imaging for multi‐echo functional MRI and distortion‐free diffusion imaging

Abstract

PurposeTo develop a single‐shot SNR‐efficient distortion‐free multi‐echo imaging technique for dynamic imaging applications.MethodsEcho planar time‐resolved imaging (EPTI) was first introduced as a multi‐shot technique for distortion‐free multi‐echo imaging. This work aims to develop single‐shot EPTI (ss‐EPTI) to achieve improved robustness to motion/physiological noise, increased temporal resolution, and higher SNR efficiency. A new spatiotemporal encoding that enables reduced phase‐encoding blips and minimized echo spacing under the single‐shot regime was developed, which improves sampling efficiency and enhances spatiotemporal correlation in the k‐TE space for improved reconstruction. A continuous readout with minimized deadtime was employed to optimize SNR efficiency. Moreover, k‐TE partial Fourier and simultaneous multi‐slice acquisition were integrated for further acceleration.Resultsss‐EPTI provided distortion‐free imaging with densely sampled multi‐echo images at standard resolutions (e.g., ˜1.25 to 3 mm) in a single‐shot. Improved SNR efficiency was observed in ss‐EPTI due to improved motion/physiological‐noise robustness and efficient continuous readout. Its ability to eliminate dynamic distortions—geometric changes across dynamics due to field changes induced by physiological variations or eddy currents—further improved the data's temporal stability. For multi‐echo fMRI, ss‐EPTI's multi‐echo images recovered signal dropout in short‐ regions and provided TE‐dependent functional information to distinguish non‐BOLD noise for further tSNR improvement. For diffusion MRI, it achieved shortened TEs for improved SNR and provided images free from both B0‐induced and diffusion‐encoding‐dependent eddy‐current‐induced distortions with multi‐TE diffusion metrics.Conclusionss‐EPTI provides SNR‐efficient distortion‐free multi‐echo imaging with comparable temporal resolutions to ss‐EPI, offering a new acquisition tool for dynamic imaging.