# Getting the centre of mass for an activation

Occasionally it is useful to get a blob's centre of mass, for instance in a binary mask where peaks are not available. This function presents a simplistic solution.

% Returns the centre of mass for blob(s) in a volume. Input either % handle from spm_vol, or path to volume. If you aren't happy with % the way the function divides the volume into blobs, you can mask % off the blobs you like manually and save each blob to its own % volume. % Use: CoM = getCentreOfMass(vol) % 27/10/2009 J Carlin, with thanks to Danny Mitchell and Russell % Thompson function CoM = getCentreOfMass(vol) if isstr(vol) vol = spm_vol(vol); end v = spm_read_vols(vol); v(isnan(v)) = 0; % Identify and number code blobs blobs = bwlabeln(v); for i = 1:max(blobs(:)) % Blob indices [x,y,z] = ind2sub(size(blobs),find(blobs == i)); XYZ = [x, y, z]; CoM(i,:) = mean(XYZ,1); end