Medical imaging is an integral component of clinical trials in oncology. For each image type, quantifiable information (referred to as quantitative imaging biomarkers) can be extracted and analyzed to answer questions about tumor types and stage, and to measure response to treatment. The most common assessment of response to therapy is to measure anatomical changes to the tumor. These changes are determined by measuring tumor size in a set of medical images before patient treatment and then measuring this same lesion in a new set of medical images after treatment, thereby measuring how much the tumor has changed with therapy. However, other quantitative imaging measures derived from functional imaging methods provide equally important physiological information about a tumor, including tumor metabolism, vascularity and cellularity. In this white paper, Median Technologies provides a guide to various measurements used in imaging in oncology trials, describing both size-based and functional metrics and the various criteria that use them.