Hi Stefanie,
It’s difficult to know from the error alone what exactly has driven the nonsensical result, so will require a bit of probing the data to diagnose. The first thing you can do is re-run the command with the -debug flag and post the results here, and we’ll see if it yields anything informative.
Would removing the nan values in the FODs solve this?
Not sure to what extent the nature of this question is actually intentional. If you have FOD images that do actually contain NaN values (which would be the exception to the rule), and the compulsory mask input to mtnormalise includes voxels for which there are NaN values in the FOD coefficients, then that could at least conceivably lead to such an error, depending on the intricacies of the code. But something would have to be putting NaN values into the FOD images… So if that turned out to be the case, while we could modify mtnormalise to ignore non-finite values, you’d also want to backtrace exactly how those NaN values made their way into your images, and how whatever mechanism you used to derive your mask image still included such voxels.
Cheers
Rob