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Dianne,
I think you ought to be able to get much better resolution than that. I have scanned a human at 1.3mm isotropic on a Siemens 3T scanner. If you are specifically interested in small nerves, it would probably be best to get as high resolution as possible and scan a limited field of view with many averages. To measure the FA of a small structure accurately, you would need at least one voxel without partial voluming (or devise a method to correct for partial voluming). I have not personally done this, but theoretically you could use higher resolution anatomical imaging to estimate the fraction of the structure that was present in the DTI voxel, and if you knew the mean FA of whatever else was in the voxel, you could estimate the FA in the structure of interest. There may be issues with such an approach that others may point out, and I could see it as difficult to get past reviewers, however, and it would rely on perfect alignment between the anatomical image and DTI (i.e. any EPI susceptibility distortion would have to be corrected). Increasing the number of directions will not compensate for poor spatial resolution. Increasing the number directions will help in reconstructing multiple fiber directions for tractography, but it sounds like you are more interested in quantitative DTI values.
Peace,
Matt.
From: FSL - FMRIB's Software Library [mailto:[log in to unmask]] On Behalf Of Dianne Patterson
Sent: Friday, September 12, 2008 10:00 PM
To: [log in to unmask]
Subject: [FSL] voxel size vs structure size
Dear Group,
We have a 3 tesla GE scanner and we get 2.6 mm isotropic voxels in the brain.
I recently talked to a colleague who would love to image nerves in the neck that are about 3 mm thick.
Can anyone tell me:
1) Whether 2.6 mm voxels would be appropriate for identifying and measuring FA along such a small diameter structure.
2) What the relationship needs to be between voxel size and structure size
3) If increasing angular resolution can compensate for the lack of spatial resolution
I appreciate your kindness and support..thankyou,
Dianne
--
Dianne Patterson, Ph.D.
[log in to unmask]
University of Arizona
SHLS 328
621-5105