(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.

(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.

(PSF) The point spread function describes the response of an imaging system to a point or impulse input. A hypothetical point object will generally have an extended (blurred) image resulting from the imaging process; this is the point spread function characterizing the imaging process. Considering any object as composed of an assembly of point objects, knowledge of the PSF permits the prediction of how the object will be imaged, assuming linearity of the imaging process.

See also Resolution, Phantom and Daily Quality Assurance.