1. A medical imaging system comprising: one or more displays; a viewer device for generating an interactive user interface screen on the display, which viewer device enables a user to simultaneously inspect selected image data of multiple patients or multiple images; a registration device which identifies a global reference image in the selected image data, and determines a registration matrix which aligns an image with the global reference image; and a group registration device which registers or aligns images of the selected groups and is programmed to perform steps of: selecting a reference image in a first group; selecting a reference image in a second group; computing registration between the images of the first and second groups as 
 M r1r2 =M r1 −1 M r2 , where M r1r2 is the registration between the images of the first and second groups, M r1 is a registration of the selected first group reference image with respect to the global reference image, and M r2 is the registration of the selected second group reference image with respect to the global reference image.