1. A computerized method to automatically analyze a selected region of interest in medical image data, comprising: providing a computerized processor with a positron emission tomography (PET) image data set comprised of voxels at respective voxel positions; in said processor, automatically generating a filtered PET image data set by assigning, to each of said voxels, an intensity value for a standardized volume of interest; in said processor, constructing, for both of said PET image data set and said filtered PET image data set, a hierarchical tree structure of voxels representing a relationship between voxel position and local maxima for all voxels having an intensity value above a predetermined threshold; in response to a user-selected position in said PET image data set entered into said processor, using the tree structure of the filtered PET image data set to identify a value and position of the local maxima of said standardized volume of interest and using the tree structure of said PET image data set to segment a region of interest therein comprised of all voxels in said PET image data set connected to the local maxima for the user-selected position that are above said threshold; and making said segmented region of interest available at an output of said processor in an electronic form that allows a visualized display of the segmented region of interest.