2.1. Current staging and limitations. WBS has been the examination of choice for evaluation of potential dissemination to bone. WBS utilizes 99mTc-labeled methylene diphosphonate (99mTc-MDP) that binds to the bone matrix formed by the osteoblasts. Gamma cameras detect the γ-radiation emitted by the decaying tracer thereby creating a 2-dimentional image depicting local osteoblast activity .