Coincidence detection is the simultaneous detection of two signals. The simultaneous detection for example of two photons, annihilation coincidence detection, is used in PET imaging.

See also Annihilation Coincidence Detection.

(ACD) Caused by positron decay and positron annihilation two photons are emitted each with an energy of 511 keV in opposite directions. The simultaneous detection of these two photons, by two detectors indicates that a positron annihilation occurred at the line of response (LOR), the path between the two detectors.
In PET imaging the annihilation coincidence detection is used to localize the tracer, e.g. F18.

See also Positron Decay and Electron Positron Annihilation.

The cerebral blood pool can be imaged with single photon emission computed tomography (SPECT) and positron emission computer tomography (PET) techniques. The used radiopharmaceuticals are technetium-99m labeled red blood cells (RCBs) for SPECT and O-15 labeled water for PET imaging. Measured can be cerebral blood volume, brain perfusion and cerebral metabolism.

See Cerebral Metabolic Imaging, Fluorodeoxyglucose, Regional Cerebral Blood Flow, Coincidence Detection, Annihilation Coincidence Detection and Cyclotron.

(LOR) Line of response is in PET imaging the path between two detectors used to localize the tracer. Based on the size of the detectors - volume of response (VOR) is used instead of LOR.

See also Annihilation Coincidence Detection.