Distortion-Corrected Diffusion MRI Using Rotated-View EPI and Joint Field-Map/Image Estimation with Gaussian Primitives

2026-06-30

AI Summary

This work addresses geometric distortions in diffusion MRI caused by B0 field inhomogeneities, which severely degrade conventional correction methods at high b-values and high acceleration factors. The authors propose a physics-driven joint estimation framework that simultaneously reconstructs distortion-free images and the underlying B0 field directly from k-space data, bypassing intermediate parallel imaging steps. By incorporating multi-shot EPI acquisitions with rotated readout directions, the method enhances correction accuracy. A key innovation lies in the explicit continuous parameterization of both the image and B0 field using Gaussian basis functions, enabling interpolation-free processing of multi-shot data, while modeling image phase as a per-shot phase factor. In vivo brain diffusion experiments demonstrate that the proposed approach substantially outperforms traditional sequential methods under high b-value and high acceleration conditions, yielding images with sharper anatomical detail, reduced noise, and excellent alignment of brain boundaries with reference structures.

Abstract

Echo Planar Imaging (EPI) is the standard acquisition technique for diffusion and functional neuroimaging, enabling rapid imaging but suffering from geometric distortions caused by B0 field inhomogeneities. Existing correction methods first reconstruct distorted images using parallel imaging, then estimate the B0 field and correct the distortion in the image domain. In this sequential process, reconstruction artifacts at high acceleration factors and low SNR at high diffusion b-values degrade B0 estimation and limit the overall correction quality. We propose a physics-informed framework that jointly estimates the B0 field and distortion-free image directly from k-space data, without depending on an intermediate parallel-imaging reconstruction for the correction. The image and the B0 field are each represented as a superposition of Gaussian primitives embedded within an MRI physics forward model. The explicit, continuous parameterization captures both smooth regions and tissue boundaries and supports rotated-view EPI acquisitions without interpolation. The diffusion-weighted image is modeled as real and non-negative, with the image phase absorbed into a per-shot phase factor. Rotated views distribute distortions across multiple phase-encoding orientations, improving point spread function isotropy and providing stronger constraints for B0 estimation. On in vivo brain diffusion EPI, the proposed method attains the closest brain-boundary agreement with a distortion-free structural reference, with the largest improvement over sequential methods at high b-value and high acceleration. Extensive visual comparisons further show improved detail fidelity and noise suppression.

Problem

• distortion correction
• diffusion MRI
• B0 field inhomogeneity
• Echo Planar Imaging
• geometric distortion

Innovation

• Gaussian primitives
• joint B0/image estimation
• rotated-view EPI
• distortion correction
• k-space reconstruction