Don't worry, this can happen. FA is, in my experience, often more sensitive. For example, when we studied patients with brain tumors, perifocal edema reduced FA in 70% of the cases (compared to the contralesional pyramidal tract) whereas radial diffusivity increased in only 56 %. Parallel diffusivity and MD are even less sensitive.
So you can put it the other way around: if all these different values would exhibit similar sensitivity to pick up changes and if they would directly translate into each other, there would be no point in using them for specific questions.
-----Ursprüngliche Nachricht-----
Von: FSL - FMRIB's Software Library im Auftrag von Jeff Riley
Gesendet: Mi 11.06.2008 00:50
An: [log in to unmask]
Betreff: [FSL] TBSS - FA with variable non-FA findings
I have a TBSS interpretation question I was hoping to get some feedback on.
I have completed a run of two groups, and have found four clusters of
decreased FA in study group vs control. I also ran non_FA for MD, axial
diffusivity and radial diffusivity. For these, only one of the FA clusters
had associated changes in MD and radial diffusivity - the other three showed
no significant differences in these parameters. I am having some difficulty
interpreting these results - how to comment on these underlying parameters
when findings are inconsistent across this analysis. I have not been able to
find any publications that address this. Have other groups found similar
results, and if so, how have you interpreted these findings? Any guidance
would be greatly appreciated.
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