Fmriprep - brain mask error?

Dear fmriprep experts,

I have just finished the preprocessing and everything seems alright since no errors were reported.
However, I have noticed that I cannot open the “sub-XX_desc-brain_mask.nii” file.

In my dataset I have 2 T1w images for each participant since I have two sessions (i.e., encoding and retrieval) that have been collected in 2 different days. I use MRIcron to open these images and when I click on it it says “Invalid floating point operation. Press OK to ignore and risk data corruption. Press Abort to kill the program”.

Basically, I cannot even explore the mask. Any idea why that is the case? I wonder whether having to merge two Tw1 images is the problem?

I am looking forward to hearing from your opinions
best wishes


After looking at the WARNINGS, I have seen that the only files that cannot be opened (that corresponds to the desc-brain_mask.nii" transformations are the ones that have been tranformed from float32 to uint8. Is there any reason why fmriprep does this?

Thank you a lot


This was noticed by other users. Please look into the following discussion and related issues:

Long story short, this is bug that will be fixed in fmriprep v20.2.4 and V21.0.0.