Dear Saad

as you suggested, I tested some of the connections with the strange values using one region as seed and another region as target (--targetmasks flag). If I compute the mean and volume (-M and -V flags) of the resulting seed_to_target files and multiply these two values I get numbers of streamlines that are larger than those reported in the network matrix, i.e. larger than 2^24.

Does this mean that something is odd with the --network flag?

Any idea how to further debug the issue?

Thanks in advance

Cheers

Jürgen

Am 05.08.2022 um 17:06 schrieb Saad Jbabdi <[log in to unmask]>:

Hi

Very strange. No idea what is happening.

One thing you can do is take one of those regions as a seed and set the others as targets (--targetmasks flag). The look at the output seed_to_target files. Using fslstats, you can calculate the total number of streamlines from the seed to reach each target (by multiplying the results of the -M and -V flags). These should map onto the corresponding row of the network matrix and should enable you to start debugging where the problem is occurring.

Cheers

Saad

From: FSL - FMRIB's Software Library <[log in to unmask]> on behalf of Jürgen Hänggi <[log in to unmask]>
Date: Friday, 5 August 2022 at 15:04
To: [log in to unmask] <[log in to unmask]>
Subject: Re: [FSL] Maximum number of streamlines is 2^24

Dear Saad

thanks for your response. I increased the number of streamlines per seed (option -P from 5000 to 6000) and again, the largest value is 2^24. With -P 6000, more connections now show this value compared with -P 5000, i.e. 98 out of 8010 connections in the matrix have a value of 2^24 and no connection showed a larger streamline count.

Thanks in advance for any advice.

Best regards

Jürgen

Am 05.08.2022 um 09:46 schrieb Saad Jbabdi <[log in to unmask]>:

Hi

That seems unlikely. If you increase the number of streamlines per seed, does that maximum also increase?

Cheers

Saad

From: FSL - FMRIB's Software Library <[log in to unmask]> on behalf of Jürgen Hänggi <[log in to unmask]>
Date: Friday, 5 August 2022 at 08:09
To: [log in to unmask] <[log in to unmask]>
Subject: [FSL] Maximum number of streamlines is 2^24

Dear FSL experts

we have run probtrackx2_gpu with the --network option to generate connectivity matrices among the 90 regions of the AAL atlas.
we then recognized that there are a lot of identical numbers of streamlines in the matrices. This number is always the largest number in the matrix (i.e. 1.67772e+07) and it is equal (apart from the fact that there are only 5 decimals in the scientific notation of the number of streamlines in the generated connectivity matrix) to 2^24.

it seems that the maximal number of streamlines is truncated to 2^24!

we are wondering whether this problem is related to probtrackx2_gpu or to parameters of our terminal / Ubuntu OS.
how to solve this problem?

Thanks in advance for any advice.
Best regards
Jürgen

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