I would say that anything below 25 directions will *NOT* be able to come up with a sensible probabilistic solution since your bvecs will greatly impact the probabilities of fiber orientation. Thus, I think you will never be able to use 6-dir data for probabilistic tractography. However, Tim may have a stronger and more informed opinion about that, and at least dtifit should be ok to use.
Von: Russ Poldrack [mailto:[log in to unmask]]
Gesendet: Mi 08.12.2004 01:30
An: [log in to unmask]
Betreff: Re: [FSL] dealing with multiple DTI runs
Thanks Andreas. Regarding the using a 6-direction data with bedpost,
is this an absolute statement (i.e, "One will never be able to use
6-direction data to do probabilistic tracking") or a relative statement
("One needs to be careful with the output of bedpost using 6-direction
data")? If the latter, can you suggest some metrics for robustness?
On Dec 7, 2004, at 4:00 PM, Automatic digest processor wrote:
> hi russ-
> 6 directions is generally too few for a robust probabilistic solution.
> w/r to 1, i would tend to average the coregistered /
> eddy-current-corrected runs and perform further computations on the
> average. (simply because it would be less time consuming.)
> w/r to 2, yes - flirt can register to the b0-image (corrratio puts up
> well with the liquor being bright on b0 but dark on the other images),
> i.e you can simply put it first to use it as the default reference
> best regards-
Russell A. Poldrack, Ph.D.
Assistant Professor of Psychology, UCLA
Franz Hall, Box 951563
Los Angeles, CA 90095-1563
email: [log in to unmask]