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

Abstract

Purpose: To develop an efficient acquisition technique for distortion-free diffusion MRI and diffusion-relaxometry. Methods: A new ACcelerated Echo-train shifted Echo-Planar Time-resolved Imaging (ACE-EPTI) technique is developed to achieve high-SNR, distortion- and blurring-free diffusion and diffusion-relaxometry imaging. ACE-EPTI employs a newly designed variable density spatiotemporal encoding with self-navigation capability, that allows submillimeter in-plane resolution using only 3-shot. Moreover, an echo-train-shifted acquisition is developed to achieve minimal TE, together with an SNR-optimal readout length, leading to ~30% improvement in SNR efficiency over single-shot EPI. To recover the highly accelerated data with high image quality, a tailored subspace image reconstruction framework is developed, that corrects for odd/even-echo phase difference, shot-to-shot phase variation, and the B0 field changes due to field drift and eddy currents across different dynamics. After the phase-corrected subspace reconstruction, artifacts-free high-SNR diffusion images at multiple TEs are obtained with varying T2* weighting. Results: Simulation, phantom and in-vivo experiments were performed, which validated the 3-shot spatiotemporal encoding provides accurate reconstruction at submillimeter resolution. The use of echo-train shifting and optimized readout length improves the SNR-efficiency by 27-36% over single-shot EPI. The reconstructed multi-TE diffusion images were demonstrated to be free from distortion (susceptibility and eddy currents) and phase/field variation induced artifacts. These improvements of ACE-EPTI enable improved diffusion tensor imaging and rich multi-TE information for diffusion-relaxometry analysis. Conclusion: ACE-EPTI was demonstrated to be an efficient and powerful technique for high-resolution diffusion imaging and diffusion-relaxometry, which provides high SNR, distortion- and blurring-free, and time-resolved multi-echo images by a fast 3-shot acquisition.

Imaging the structural connectome with hybrid diffusion MRI-microscopy tractography

“…This may again be related to the fact that the hybrid fibre orientations are more directly related to myelinated axons, where myelinsensitive microscopy is typically used to characterise fibre fanning patterns ex vivo, and where dendrites complicate dMRI modelling at the grey-white matter boundary. Whether the results can be extrapolated to in vivo data needs further investigation, for example using recently proposed high-resolution dMRI protocols such as Romer-EPTI which is able to acquire submm resolution in an achievable scan time 58 . Considering the global volume difference between humans and macaques (macaque brain volume is ~1/12 of the human brain volume), the spatial resolutions we used (1mm, 0.6mm and 0.4mm) are approximately equivalent to the 2.5, 1.5, and 1 mm in humans, roughly corresponding to resolutions achievable in the clinic, in typical research data and among the highest achievable resolution so far.…”

Single-shot Echo Planar Time-resolved Imaging for multi-echo functional MRI and distortion-free diffusion imaging

“…The original multi-shot EPTI (ms-EPTI) mostly targets anatomical imaging and high spatial resolution applications. For example, it has been demonstrated to provide high efficiency for fast multi-contrast imaging (47,48), multi-parametric quantitative MRI (49,50), high-resolution functional MRI (51), highresolution distortion-free diffusion imaging (52)(53)(54), and myelin water imaging (55).…”

Accelerating joint relaxation‐diffusion MRI by integrating time division multiplexing and simultaneous multi‐slice (TDM‐SMS) strategies

“…Ning et al 21 proposed a similar framework and introduced a simplified method, named REDIM, to estimate the joint moments of relaxation and diffusion coefficients. We note that the coupling between T 1 , relaxation time and diffusivity have also been investigated to characterize tissue microstructure 22–26 . For example, Melbourne et al 24 and Slator et al 25 demonstrated the feasibility of combined diffusion and T 2 or relaxation MRI on placenta for separating signals from fetal and maternal circulations, and identifying dysfunction, respectively.…”

“…We note that the coupling between T 1 , T * 2 relaxation time and diffusivity have also been investigated to characterize tissue microstructure. [22][23][24][25][26] For example, Melbourne et al 24 and Slator et al 25 demonstrated the feasibility of combined diffusion and T 2 or T * 2 relaxation MRI on placenta for separating signals from fetal and maternal circulations, and identifying dysfunction, respectively. Benjamini et al 23 investigated combined T 1 -T 2 -diffusion changes linked to diffuse axonal injury caused by trauma in the human brain.…”