Hi Linda,

Assuming you want to alter an ROI with a value
of 7 to one with values of 71 and 72 say, then
use 3dcalc. Ignoring the precise alteration,
consider:

3dcalc -a input+tlrc -expr "a*(1-equals(a,7)) + 71*equals(a,7)" ...

That would leave the dataset as it was, except
for changing any 7 to 71.

Then you could expand that 71 to be something
like: (71*ispositive(j-53)+72*ispositive(54-j)).
That would assume that A-P is the second axis
(specified using "j") and that slice 53 is your cutoff.

Alternately, use the y-coordinate. If it is RAI
orientation, consider:

(71*ispositive(y-5)+72*ispositive(5.1-y))

Anyway, give those a little try. Note that i,j,k
are pre-defined variables for the slice indices,
while x,y,z are those for coordinates.

- rick