Averaging two TDI maps

I used tckmap to create TDI maps from two different shells of the same subject.
I wanted to average these two maps but I got the error "[ERROR] Dimensions of image 1400_TDI.mif do not match those of first input image 700_TDI.mif" then I used mrinfo and realized that the dimension and transform are slightly different between the two maps.
Any idea why this happens? and in case that this is normal how I can average the TDI maps?


This will most likely be due to your use of the -vox option only in the tckmap call. When that’s all it’s given, tckmap will try to figure a suitable bounding box for the output image based on the track data (by default, the first 10k streamlines, from memory). Since the tractography is typically at least a bit random, the bounding box will generally come out slightly different for different tractograms.

To fix this, the simplest is probably to add the -template tdi1.mif option to the second tckmap call, where tdi1.mif is the output of the first tckmap call.