Hi,
You can certainly parameterise the FA value along tracts and then
compare this across subjects, but TBSS probably doesn't help you
achieve that very easily. You would probably want to mask the FA
image with the tract and then calculate FA as a function or (maybe
fractional) distance along the tract , reducing a single subject's
data to a 1D vector which then you could compare across subjects.
Yes, you might want to weight the included FA values according to the
tract strength values, or just threshold the latter to create a mask.
Cheers, Steve.
On 13 Aug 2007, at 02:39, Ravi Shetty wrote:
> Hi, I had a few questions I was hoping some of you could answer. I
> was wondering if it is possible to
> use TBSS on Probtrack results? For example if I wanted to compare
> the FA values of the probabilistic
> pathways from the corpus callsoum to the motor cortex between
> subjects. Should I use a different
> file to start TBSS (like mean_fsamples)? In the FSL TBSS guide they
> use the dti_FA file obtained from
> DTIFit but that data has yet to be bedposted or run through
> probtrack so I am assuming that would
> not be what I want to use. Another question I have is in regards to
> the calculation of the probabilistic
> FA values. Are the FA values weighted according to the probabilty
> of the sample path? By that I mean
> if a sample path has a certain probability then would the FA value
> for that path be multiplied by that
> probability or are all the FA values of all the possible paths in
> the distribution weighted equally and
> then averaged? Sorry for the long and probably somewhat wordy post.
> Thanks for your time.
>
> -Ravi
------------------------------------------------------------------------
---
Stephen M. Smith, Professor of Biomedical Engineering
Associate Director, Oxford University FMRIB Centre
FMRIB, JR Hospital, Headington, Oxford OX3 9DU, UK
+44 (0) 1865 222726 (fax 222717)
[log in to unmask] http://www.fmrib.ox.ac.uk/~steve
------------------------------------------------------------------------
---
|