I have been trying to use Option 2 in Seeding Options ( Documentation/Nightly/Modules/UKFTractography - Slicer Wiki). I used Tracula generated probability distribution volume, normalized it to have 0 to 1 values as the documentation requires and tried float32 and uint8 +importing it as nii.gz and as .nrrd. Regardless, UKF tractography module outputs “Unsupported data type for seed file!”. Unfortunately, i could not find any requirements for data format in the module’s documentation.