hi Tim - it turns out that I had an error in my bvals file. After
fixing that the FA maps look fine. Sorry about the confusion.
cheers
russ
On Dec 10, 2004, at 11:47 PM, Tim Behrens wrote:
> Hi Russ -
>
> Yes - it sounds like something is wrong!! What do your MD values look
> like? - are they positive? If you look at oyuor data in fslview do the
> diffusion weighted scans have lower signal than the non-weighed ones?
>
> Anyway, if you can tar up the directory, and stick it on the web
> somewhere, I can take a quick look.
>
> Thanks
>
> Tim
>
> On Fri, 10 Dec 2004, Russ Poldrack wrote:
>
>> Hi - I am having some odd results using dtifit on some of our data.
>> When I compute FA maps using an older custom program, I get very
>> reasonable results, with FA ranging from zero to one and with high FA
>> values where they should be (e.g., corpus callosum). When I run
>> dtifit
>> on the same data, I get some odd results. First, the FA values in the
>> corpus callosum are very low. Second, the range of FA values is a bit
>> strange. Within voxels that are not exactly zero-valued, the minimum
>> FA value is about 0.35; this compares to our previous results where
>> the
>> minimum FA value was around .01. In addition, the maximum FA value is
>> greater than zero (1.15 in this dataset).
>>
>> Any ideas as to what might be causing this?
>>
>> cheers
>> russ
>>
>>
>>
>>
>> ---
>> Russell A. Poldrack, Ph.D.
>> Assistant Professor of Psychology, UCLA
>> Franz Hall, Box 951563
>> Los Angeles, CA 90095-1563
>> email: [log in to unmask]
>> phone: 310.794.1224
>> fax: 310.206.5895
>> web: http://www.poldracklab.org/
>>
>
> --
> -----------------------------------------------------------------------
> --------
> Tim Behrens
> Centre for Functional MRI of the Brain
> The John Radcliffe Hospital
> Headley Way Oxford OX3 9DU
> Oxford University
> Work 01865 222782
> Mobile 07980 884537
> -----------------------------------------------------------------------
> --------
>
---
Russell A. Poldrack, Ph.d.
Assistant Professor
UCLA Department of Psychology
Franz Hall, Box 951563
Los Angeles, CA 90095-1563
phone: 310-794-1224
fax: 310-206-5895
email: [log in to unmask]
web: www.poldracklab.org
|