Deconvolution-Based Distortion Correction Of Epi Using Analytic Single-Voxel Point-Spread Functions

Purpose: To develop a postprocessing algorithm that corrects geometric distortions due to spatial variations of the static magnetic field amplitude, B-0, and effects from relaxation during signal acquisition in EPI.Theory and Methods: An analytic, complex point-spread function is deduced for k-space trajectories of FPI variants and applied to corresponding acquisitions in a resolution phantom and in human volunteers at 3 T. With the analytic point-spread function and experimental maps of B-0 (and, optionally, the effective transverse relaxation time, T-2*) as input, a point-spread function matrix operator is devised for distortion correction by a Thikonov-regularized deconvolution in image space. The point-spread function operator provides additional information for an appropriate correction of the signal intensity distribution. A previous image combination algorithm for acquisitions with opposite phase blip polarities is adapted to the proposed method to recover destructively interfering signal contributions.Results: Applications of the proposed deconvolution-based distortion correction ("DecoDisCo") algorithm demonstrate excellent distortion corrections and superior performance regarding the recovery of an undistorted intensity distribution in comparison to a multifrequency reconstruction. Examples include full and partial Fourier standard EPI scans as well as double-shot center-out trajectories. Compared with other distortion-correction approaches, DecoDisCo permits additional deblurring to obtain sharper images in cases of significant T-2* effects.Conclusion: Robust distortion corrections in EPI acquisitions are feasible with high quality by regularized deconvolution with an analytic point-spread function. The general algorithm, which is publicly released on GitHub, can be straightforwardly adapted for specific EPI variants or other acquisition schemes.