The use of medical imaging for evaluation of drug efficacy and safety has been increasing in recent years.The value of medical imaging lies in the ability to make objective assessments of either definitive endpoints (e.g., inci dent fracture in osteoporosis, structural damage in arthritis) or surrogate endpoints (e.g., tumor response in oncol ogy) in clinical trials.The imaging endpoints can be more sensitive measurements of treatment response which al low clinical trials to be run with fewer subjects or shorter duration reducing the time and potentially the cost of a clinical trial.Not all image-based assessments are accepted by regulatory authorities as appropriate for primary end points in Phase Ⅲ.Nevertheless the benefits of imaging can also be applied to early phase development where ima ging endpoints can be used for internal decision making to continue or terminate a development program or select the proper dose to use in Phase Ⅲ trials.