#!/bin/tcsh
Here is a short script to compute the MAD given a dataset and a mask.

# MAD.csh
# usage;
# MAD.csh dset+orig mask+orig
# compute MAD = Median absolute deviation over a mask at each time point
# MAD = median(abs(a-median))
set dset = $1
set mask = $2
set nv = `3dnvals $dset`
@ nv --
rm -f MAD_???+orig.*
foreach sb (`count -digits 3 0 $nv`)
set median = `3dBrickStat -median -mask $mask $dset"[${sb}]" \
| awk '{print $2}' `
3dcalc -a ${dset}."[${sb}]" -b $mask -expr "step(b) * abs(a - $median)" -prefix MAD_$sb \
>& /dev/null
set MAD = `3dBrickStat -median -mask $mask MAD_${sb}+orig | awk '{print $2}'`
echo "MAD for sub-brick $sb = $MAD"
end