Dear Freesurfers,

I am trying to perform an operation with .mgh files by using mris_calc. This is my operation:

(image1 - image2)

_______________

      (image2)

First I am using the command:

mris_calc -o $hemi.FILE1.mgh $hemi.image1.mgh sub $hemi.image2.mgh

And then:

mris_calc -o $hemi.FILE2.mgh $hemi.FILE1.mgh div $hemi.image2.mgh

Is this procedure correct? 

Also, I have read this information about the command mris_calc functions: "Note: <file1> and <file2> should typically be generated on the same subject"

But actually, my image1 belongs to a single subject, while image2 is a mean of images from many different subjects (obtained using mri_concat --mean).

Is mris_calc going to work in this case?

Thank you very much for your help,

Valeria