In many cases, researchers already have a priori selected areas/regions which are candidates for testing specific hypothesis, which gives greater detection power (at least when, on the other hand, researchers apply customary multiple-comparison correction algorithm if they decide to perform whole-brain searches for effects that match their hypothesis!).
Often these regions of a priori interest are given as an estimate of a central coordinate around which a spherical shape is defined with a given radius. This method allows to create ROIs that conform with that notion.
VOI::AddSphericalVOI - add a spherically shaped VOI to the object FORMAT: [voi = ] voi.AddSphericalVOI(c, r); Input fields: c 1x3 coordinate (center) r 1x1 radius (must be > 0 and < 128) Output fields: voi VOI with added VOI (integer coordinates only!)
To add one specific ROI to a new VOI object around, say, coordinate (-24, -4, -22) (the Talairach Atlas resolves to the left Amygdala on that coordinate) with a radius of 6mm, you can use the following code:
% create VOI object voi = xff('new:voi'); % add ROI voi.AddSphericalVOI([-24, -4, -22], 6);
To add multiple VOIs (e.g. from a table of coordinates), you could use this:
% create VOI object voi = xff('new:voi'); % coordinates are in a Cx3 table, ctab, and the radius is fixed at 8mm % alternatively, the radius could be in column 4 in a Cx4 table % iterate over coordinates in table for cc = 1:size(ctab, 1) % add coordinate voi.AddSphericalVOI(ctab(cc, 1:3), 8); % or alternatively: % voi.AddSphericalVOI(ctab(cc, 1:3), ctab(cc, 4)); end