Hi Phil,

Having a "normalized" peak of around 600 is not strange at all,
even with only small movement. Voxels just outside the brain
can have values bouncing around 20. Even a small movement
can temporarily bounce this into the hundreds, while the average
sits at 20. A temporary bounce to 220 is a 1000% signal change.
And any ghosting can produce very large values that are not even
close to the brain.

In HowTo #5, 3dAutomask was used to mask out the non-brain
voxels. The maximum (remaining) normalized peak was around
200 (100% change) for most of the 10 runs. Without 3dAutomask,
the peak was generally around 13000 (because of averages that
were basically at zero), and just knocking off voxels with averages
less than 50 drops the maximum normalized value to under 500.

At any rate, some sort of Automask procedure seems reasonable.
See the script for HowTo #5 for example:

[afni.nimh.nih.gov]

In text: [afni.nimh.nih.gov]

- rick