Hi,
We would like to correct EPI distortion in diffusion MRI *and* minimize blurring from resampling. There are several ways to correct EPI distortion, depending on what other images are available (e.g. flipped phase encoding or undistorted T2w -> topup, T1w -> BrainSuite), but the results fall into two distinct camps of being in either the T1w space (high resolution) or undistorted dMRI space, which mainly means dMRI-sized voxels. Our analyses often combine the dMRI and T1w images in some way, but we usually have a choice of registering and resampling the dMRI images to the T1w images, or the T1w images (or segmentations, or atlas regions) to the dMRI images. Both ways work, but presumably one of the spaces is better to work in. Does anyone have experience with using both low and/or distorted images (dMRI) and high resolution undistorted images (e.g. T1w) together, and have any insights?
Theoretically each additional resampling step introduces some degradation, so "native" space is the right one for dMRI.
However,
* The T1w voxels are so much smaller than the diffusion voxels that the resampling of dMRI into T1w space is typically excellent.
* The undistorted diffusion images *are* resampled, so they are not really in native space. If resampling is necessary it is better to resample finely (i.e. use T1w space). On the other hand, many parts of the brain, like the parietal lobe and motor-sensory strip, are relatively unaffected by EPI distortion and may be left in nearly native space after undistortion with topup, if head motion and eddy current distortion are not a large problem.
We look forward to reading your opinions,
Rob
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Robert I. Reid, Ph.D. | Sr. Analyst/Programmer, Information Technology
Aging and Dementia Imaging Research | Opus Center for Advanced Imaging Research
Mayo Clinic | 200 First Street SW | Rochester, MN 55905 | mayoclinic.org
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