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Dear FSL experts,

I have a question about the third procedure of TBSS analysis: tbss_3_postreg (https://fsl.fmrib.ox.ac.uk/fsl/fslwiki/TBSS/UserGuide#tbss_3_postreg).
Generally, the manual suggests tbss_3_postreg -S  (derive the mean FA and skeleton from the actual subjects we have).
 Alternatively, if I wish to use the FMRIB58_FA mean FA image and its derived skeleton, instead of the mean of my subjects in the study, use the -T option: tbss_3_postreg -T

So, if I use tbss_3_postreg -S, because the value in each FA map ranges from 0 to 1, so the mean FA image and mean FA skeleton is also ranges from 0 to 1. Then, in the subsequent procedure, we can directly input tbss_4_prestats 0.2 to threshold the mean FA skeleton image using the chosen threshold 0.2.

If I use tbss_3_postreg -T, then the FMRIB58_FA template is treated as mean FA image and then the skeleton is derived. However, in this manner, the value in the mean FA image and skeleton image range from hunderd to thousand (because the value in the FMRIB58_FA template ranges hunderd to thousand). Thus, if we also set the threshold as 0.2 (tbss_4_prestats 0.2), this threshold is invalid.

My questions here are that how to set the threshold (tbss_4_prestats ) if I use the tbss_3_postreg -T option? When should we use this option?
In my view, it is very inconvenience to set threshold (tbss_4_prestats) if I use tbss_3_postreg -T. So, I am just curious that why this option exists?

Any help would be greatly appreciated!

Best,
Feng

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