A system and method for performing quantitative lesion analysis in molecular breast imaging (MBI) using the opposing images of a slightly compressed breast that are obtained from the dual-head gamma camera. The method uses the shape of the pixel intensity profiles through each tumor to determine tumor diameter. Also, the method uses a thickness of the compressed breast and the attenuation of gamma rays in soft tissue to determine the depth of the tumor from the collimator face of the detector head. Further still, the method uses the measured tumor diameter and measurements of counts in the tumor and background breast region to determine relative radiotracer uptake or tumor-to-background ratio (T/B ratio).