Massachusetts General HospitalIshtiaq M.Thanks,Hi experts,I am trying to figure out the units on the tag-control relative perfusion image, created through --diff by asl_file. How is this computation done? What we have done before is calculate a "percent signal change" by taking the average of all control images, average of all tag images (for each voxel) then compute (avg. control minus avg. tag) divided by avg. control multiply by 100 to get the relative perfusion in % signal change units. Just wondering how asl_file did the computation and how/if I can get % signal change through asl_file.