Single-Photon Emission Computed Tomography

A nuclear medicine imaging technique that builds a three dimensional picture of how a radioactive tracer is distributed inside the body by rotating a gamma camera around the patient and recording the single gamma photons the tracer emits from many angles, then reconstructing the angled recordings into cross-sectional images. A small amount of a radioactive tracer, chosen to concentrate in the organ or tissue under study, is injected into the patient beforehand, and the resulting images show where the tracer has gathered, which can reveal blood flow, organ function, or disease activity that a purely structural scan such as an X-ray or a plain CT scan would not show. The technique grew out of earlier planar nuclear medicine imaging, which produced only a single flat image from one angle, once computer reconstruction methods developed for X-ray computed tomography in the 1970s were adapted to reconstruct the rotating gamma camera's many recordings into full cross-sectional slices. It is widely used to assess blood flow to the heart muscle, to evaluate the brain in epilepsy and some forms of dementia, and to look for bone disease, and is often combined in a single scanner with a conventional CT scan so the functional tracer image can be matched precisely to the patient's own anatomy.