Scintigraphy is form of diagnostic imaging which involves the administration of radioactive substances. Whereas in radiology and computed tomography external radiation passes through the object being studied, the radioactive isotopes administered intravenously prior to scintigraphy cause radioactive emition directly from the object. This radiation is detected by a special camera (gamma camera) and represented as an image on a screen. A higher concentration of radioisotopes is found in tissue that is subject to increased function. This may be due to physiological factors (joints always show more activity than bone shafts) or may be the result of pathological changes such as inflammation or fracture repair. These areas will show up as 'hot spots' - areas of increased radioactivity.