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Region of Interest Drawing and Usage in AFNI
¥Goal:
Manually select Regions of Interest (ROIs) based on anatomical structures, then analyze functional datasets within
these regions
HE.g., Someone doing a study on emotion may want to draw
an ROI mask that includes the amygdala only in
order to analyze the voxels that fall within that brain region
HThis method relies on Ôa prioriÕ assumptions about
localization of brain function
¥Alternative procedure for selection of ROIs: Analyze functional dataset for entire brain first, then focus on geometrically connected
clusters of ÔactivityÕ (supra-threshold
voxels in some functional statistical map)
Hi.e., analyze the entire brain first and then pinpoint
interesting areas of activity and do further
analyses on those areas (3dclust or 3dmerge can assist you in
finding those larger ÒblobsÓ or clusters of activity)
åEven with this method, you might want to manually adjust
the ROIs (i.e., add or delete some voxels
in the ROI mask)
¥ROIs are stored as regular AFNI datasets (i.e., with a
.HEAD and .BRIK file); it is only the
user (you) that decides whether a particular dataset is a ROI mask
HNonzero voxels are ÒinÓ the mask; zero voxels are
ÒoutsideÓ