Issue with Mean diffusivity scalar measurement

Dear all,
I’m facing issues when trying to create a Mean Diffusivity output from my DTI data.
I’m using Slicer 4.10.1 and the DMRI Extension and imported my data (acquired at 3T, Siemens Skyra, 41 gradient directions) using DWIConvert. Then I followed the DTI tutorial by Sonia Pujol and was able to create a brain mask and to estimate a tensor that looked ok. However, I have problems to calculate a Mean Diffusivity map from my data. I used Diffusion --> Quantify --> Diffusion Tensor Scalar Maps as described, but the MD map I get has some “blank” spaces/missing values (several pixels are displayed like the background so that it looks as if the map has holes).
When calculating trace or FA, the maps look fine and don’t show any missing values.
How can I fix this?
Thanks a lot for your help!