Hi Fred - As with any probabilistic method, volume here is a measure of
the spread of the probability distribution of the pathway (i.e. of
path.pd.nii.gz), so it can be interpreted as the amount of uncertainty in
the data. A more spread out distribution means more uncertainty, a tighter
distribution means less uncertainty.
Please note that TRACULA performs tractography in each subject's native
DWI space, so volume/length are not calculated in a common/normalized
space for all subjects. So beware when comparing volume/length across
subjects.
If you use the weighted FA/MD/etc measures, these are weighted by the
value of the probability distribution at every voxel, so they are the mean
values in a probabilistic sense.
Hope this helps,
a.y
On Wed, 19 Jun 2013, Fred Sanders wrote:
Dear DTI experts,
I am trying to understand how to interpret tract length volume
measurements that TRACULA provides. For example, let’s say a clinical
population differs from a control group in mean FA of a particular
tract, and tract length volume are comparable across the 2 groups.
I think this would support the notion that the tract’s diffusion
properties are indeed different across the two groups and that the FA
finding are unlikely to be an artifact of probabilistic tractography.
Is this a correct interpretation? Conversely, if group differences in
tract volumes were detected, would you recommend comparing mean FA
across the two group while covarying for tract volume?
Thanks!
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