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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.

Method reference ('voi.Help('AddSphericalVOI')')

 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));
voi.addsphericalvoi.txt · Last modified: 2010/06/28 19:07 by jochen