Hi Dillan - Thank you for your support!
Because the maximum value can sometimes be an outlier, we use the values of the 99th percentile instead. In the absence of an outlier this would be very close to the maximum.
Best, a.y On Tue, 26 Jul 2016, Newbold, Dillan wrote:
Hi everyone, I’m having a little trouble understanding the exact meaning of the 20% default threshold used in the freeview -tv option and dmri_pathstats --pthr. I’ve seen multiple threads where Anastasia said that it is 20% of the maximum value in the probability distribution—which corresponds to the maximum number of sample paths intersecting a single voxel—but the default thresholds I’ve seen set by the -tv option are generally lower than that. For example, I have one subject in whom the right CST has a maximum value in its path.pd.nii.gz file of 300. I would expect based on what I’ve read in the mail archives that the threshold would be set at 60, but when I open the merged file with the -tv option the default threshold for the right CST is 35. My current best guess is that the default threshold is set to produce a volume that has a probability sum equal to 20% of the sum of the pre-threshold volume. (That is, the sum of intensities of all voxels in the path.pd.nii.gz file should be 5 times the sum of the voxels above the default threshold.) Is that accurate? Thanks for all you’ve done to develop this tool. It’s brilliant and I want to understand as much of it as I can. -Dillan _______________________________________________ Freesurfer mailing list Freesurfer@nmr.mgh.harvard.edu https://mail.nmr.mgh.harvard.edu/mailman/listinfo/freesurfer
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