mALFF-1

Dear All
Hi,
1- Why we should use mALFF-1 images for one sample t-test? why we can't use mALFF or ALFF images?
2- When I run 'Image calculator' in REST and add 20 mALFF images as group images and expression was "g1-1". The below error occured in matlab workspace:
??? Error using ==> horzcat
CAT arguments dimensions are not consistent.

Error in ==> rest_WriteAnalyzeImage at 79