Dear
FSL experts
I
have a few questions about the interpretation of the waytotal number and would really
appreciate if someone would help me on this.
My
question is: are there any studies that have correlated the waytotal number
with anatomical pathway strength or any functional significance based on the underlying
pathway from which the waytotal is derived?
In
other words, is it safe to use waytotal number as an index of the anatomical pathway
strength?
My
previous experience tracking on corticospinal tract kind of says no, because it
was quite often to see that waytotal number in the left CST was 3 (or even
higher) times larger than that in the right CST in one subject and vice versa
in another subject and we could not correlate handedness measures with the
waytotal numbers .
On
the other hand, it seems that it does reflect a certain degrees of connectivity
strength. One example is as follows:
Consider
the following two situations:
Case1:
we have two cortical target masks, one at the thalamus and another at precentral
gyrus, among which a strong pathway is supposed to exist between (CST pathway).
We run probtrackx using the whole brain white matter as the seed mask and two
cortical masks as the target masks ( 1000 samples per voxel).
Case2:
we have two cortical target masks, one at the superior frontal cortex and
another at the occipital cortex (among which a relatively weak connection exists) and again the whole brain white matter
mask is used as the seed mask and two cortical masks are used as the target
masks.(1000 samples per voxel are sent).
A
very possible result after running probtrackx on the above two cases is that
we get higher waytotal number in the case 1 than that in the case 2on a
population level, even when
the areas of the cortical target masks are considered in the analysis. This should also probably reflect some real white matter anatomical
differences in the brain as we do see that axons at the CST are much more
coherent and their diameters are much larger.
Anyway,
I would really appreciate if anyone would give any thoughts or comments on this
question
Thank
you all in advance!
Longchuan
