Some things to keep in mind about DTI acquisitions:  It’s better to have more directions and less averages (30 directions would be good, 60 would be great).  You want each individual average to be saved separately so you can remove subject motion.  You don’t want your scanner to interpolate the images.  You want your voxels to be isotropic if possible (many people use 2mmX2mmX2mm).  It is better to correct the EPI distortion with a field map or other method.  The scans do not have to be in the same plane or have the same resolution, but ideally you would correct for any distortion in both and then register them to your anatomical scan with a 6 degrees of freedom (or rigid body) approach.  




From: FSL - FMRIB's Software Library [mailto:[log in to unmask]] On Behalf Of Dianne Patterson
Sent: Thursday, March 05, 2009 7:26 PM
To: [log in to unmask]
Subject: [FSL] dti and fmri: newbie setup issues


Dear Group,

I've been doing dti analyses for a little over a year now.
Some colleagues and I are intrigued by the possibility of doing connectivity sorts of analyses.
They have an fmri protocol they are about to collect pilot data for, and we thought we'd tack on a dti sequence to this.

Are there any pitfalls/considerations that we should be aware of?
For example, is there any reason to be concerned with making sure the dti and fmri scans are in the same plane or have the same resolution?

Our fmri sequences are spirals, but our dti sequences are normal epis with the associated distortions.

Any suggestions would be greatly appreciated...we don't want to re-invent the wheel here.



Dianne Patterson, Ph.D.
[log in to unmask]
University of Arizona
SLHS 328