I have never used Sleuth or Brainmap, so I don't know how chopping up your data will affect performance of the tool.

Two ideas that come to mind:
1) if you know where your region is, you could use 3dcalc commands with i,j,k or x,y,z values to divide the brain into quadrants, and then select those. In the following, the "i", "j" and "k" letters are literally those, but you would have to put in some number values for X0 and Y0, which would represent (integer) slice numbers:

3dcalc -a ROI_SET -expr 'a*step(X0 - i)*step(Y0 -j)' -prefix my_ROI_01.nii.gz
3dcalc -a ROI_SET -expr 'a*(1-step(X0-i))*step(Y0 -j)' -prefix my_ROI_02.nii.gz
3dcalc -a ROI_SET -expr 'a*(1-step(X0-i))*(1-step(Y0 -j))' -prefix my_ROI_03.nii.gz
3dcalc -a ROI_SET -expr 'a*step(X0-i)*(1-step(Y0 -j))' -prefix my_ROI_04.nii.gz

... and be sure to check visually3dcalc-ically that all parts are accounted for, i.e., the sum of these gives your original set. This would involve knowing the center of mass of your ROI, probably, for putting X0 and Y0 values that are useful; you could get that with 3dCM.

2) You could make a random data set of four values, and then assign those overlaps to carry your volumes:

# Makes a data set of size ROI_SET whose integer voxel values are uniformly sampled from the inclusive interval [0..3]. 
3dcalc -a ROI_SET -expr 'iran(3)' -prefix RANDOM.nii.gz -overwrite
# now use those to parcellate the dset/region:
3dcalc -a ROI_SET -b RANDOM.nii.gz -expr 'a*equals(b,0)' -prefix my_ROI_01 -overwrite
3dcalc -a ROI_SET -b RANDOM.nii.gz -expr 'a*equals(b,1)' -prefix my_ROI_02 -overwrite
3dcalc -a ROI_SET -b RANDOM.nii.gz -expr 'a*equals(b,2)' -prefix my_ROI_03 -overwrite
3dcalc -a ROI_SET -b RANDOM.nii.gz -expr 'a*equals(b,3)' -prefix my_ROI_04 -overwrite

The benefit of this method is that your regions should be roughly the same sized by random luck (theoretically), regardless of your data set's placement in space. Also, you don't need to know its center of mass. (And again, you should doublecheck that everything went well by summing up your parcels and subtracting the result from the original, making sure that you get zero everywhere.)

Again, how either method could affect your output results, I have absolutely no idea.

--pt



Edited 2 time(s). Last edit at 01/02/2017 10:14AM by ptaylor.