In methods and an apparatus for analyzing a selected region of interest in medical image data of a subject, an initial image data set is obtained, and the initial image data set is filtered to generate a filtered data set. The filtering includes computing, for each voxel of the initial image data set, a value of intensity for a standardized volume of interest centered on that voxel. A user selection of a region of interest in the initial image data set is registered, and from the filtered image data set a value of intensity for the selected region of interest is computed.