Well in this case it should be quite simple since you already calculated the values - since you're somehow calculating the values for each voxel already - you should know how to put the values back into the array that is essentially a nifti image ?
I think I just don't understand the issue. How did you extract timecourses of all the voxels and calculated the value? What was the tool you used? In what form did you obtain these timecourses? (it was not an array of nifti images as I understand, right?)
As for the GUI for such an operation - I think I do not know any other tool for that than spm image calculator, but I'm afraid the setup would be quite horrific to calculate some complex measure on a long time-series of images..
But if I am mistaken SPM experts should correct me
EP
