Hi Benxamín - Those can occasionally arise due to noise. You're more likely to see them if you're looking at single voxel values than average values over multiple voxels. That sequence of values in the .9-1 range does look quite high though. Another possibility would be miscalculation due to incorrect b-values.

a.y ________________________________ From: freesurfer-bounces@nmr.mgh.harvard.edu freesurfer-bounces@nmr.mgh.harvard.edu on behalf of Benxamin varela lópez benxatic@gmail.com Sent: Wednesday, December 18, 2019 1:06:38 PM To: freesurfer@nmr.mgh.harvard.edu freesurfer@nmr.mgh.harvard.edu Subject: [Freesurfer] FA index greater than 1

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Dear freesurfer experts

I am a beginner in DWI data processing and my question may be absurd, if so, I apologize in advance.

I am using TRACULA for the analysis of my DWI data. Reviewing the outputs of the statistics for the FA index I realized that some of these are greater than 1. Considering that FA oscillates between the values 0-1, how is this possible?

I send to you in attached the .txt with the average FA values for the Forceps Minor where the "anomalous" values can be observed.

Thanks in advance

Best regards

Benxamín