1. A method of identifying a region of interest in a medical image of a subject, comprising: determining at least one local maximum region of the image for which a value of a given variable is a local maximum value; registering a user-selection of an initial voxel in the image; and selecting, as said region of interest, a connected set of voxels for which values of the given variable are greater than a threshold, the selected set of voxels comprising a first local maximum region at a distance from the user-selected voxel, and the threshold being a given fraction of the local maximum value of the first local maximum region in the set.