1. A computer-implemented method for image processing, the method comprising: receiving a first medical image from a data storage device, said first medical image comprising a plurality of image voxels and representing a plurality of tissue regions of a subject; automatically determining a reference value based on said first medical image, said reference value capable of providing a range of background level of voxel intensity values within at least one non-disease tissue region of said subject; generating a disease threshold based on the reference value; identifying portions of the medical image corresponding to disease-tissue regions according to said disease threshold, each of said portions comprising a plurality of connected image voxels in said medical image; and entering data encoding said disease-tissue regions into a database for subsequent comparisons.