1. A method, comprising: receiving a first image of a prostate, wherein the first image is acquired with a first imaging modality and is segmented to show a border of the prostate; acquiring a second image of the prostate, wherein the second image is acquired with a second imaging modality; performing a first registration to match an orientation of the first image to an orientation of the second image and a feature of the prostate in the first and second images; acquiring third images of the prostate, wherein the third images are acquired with the second imaging modality and compounded into a three-dimensional (3D) image; segmenting the prostate in the compounded 3D image to show a border of the prostate, wherein the segmentation uses parameters of the first registration and a binary mask of the prostate in the first image; performing a second registration and then a third registration different from the second registration on distance maps generated from the prostate's borders, wherein the first and second registrations are based on a biomechanical property of the prostate; and mapping a region of interest in the first image to the compounded 3D image or a fourth image of the prostate acquired with the second modality, wherein the mapping is based on a result of the second and third registrations.