Hi,
with respect to our tractography research project I had a discussion with a
colleague about thresholding the probtrack results normalized by waytotal. We
are not particularly conviced by using arbitrary fixed threshold, i.e. 5%,
10%, or even as low as 2%, as has been discussed in this mailing list as
well. Different fibers may have different "trackability" and using the same
threshold may thus yield over or under estimation of the track volume and
show/hide intrahemispheric asymmetry.
Instead, what we thought could be used in place of the fixed threshold is
following:
1. for each probtrack output, create a histogram of the track probability
(probtrack normalized by waytotal), which could represent a "track
probability distribution function". Even the full set of values could be used
here, without binning.
2. fit the probability distribution function to a known distribution
functions, i.e. exponential, gamma, normal
3. use a descriptive statistical parameter (percentile, STD, ...) of a given
distribution as a threshold.
The problem with this approach is in 2. that the "track probability
distribution looks" very much like double exponential, with steep initial
decay and very long tail and I haven't been able to test it successfully
against either exponential nor normal distributions using K-S test.
I would appreciate the comments and thought on this approach and possibly how
to go further with it.
Thanks,
Martin
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