Monte Carlo Calculations of the Detection Efficiency of Arrays of Nai(Tl), Bgo, Csf, Ge, and Plastic Detectors for 511 Kev Photons

In positron emission tomographs employing arrays of detectors, the useful detection efficiency and spatial resolution depend on the size and type of detectors, the septa between the detectors, the angle of incidence, and the extent to which the pulse height selection rejects multiple detector interactions. To determine the relative effect of these factors a Monte-Carlo computer code was developed that tracks the Compton and photoelectric interactions of photons incident on a linear array of detectors. The photon is tracked until it either escapes the array or is photoelectrically absorbed in a detector or septum. A photon is successfully detected whenever the energy-loss threshold is exceeded in only one detector. Results are tabulated for bismuth germanate (BGO), NaI(Tl), CsF, germanium, plastic and lead loaded plastic detectors from 0.1 cm X 1 cm X 1 cm to 5 cm X 10 cm X 10 cm; for lead septa between detectors; for energy loss thresholds from 0 to 511 keV; and for angles of incidence from 0 to 30 degrees. We show that for a given detector size, BGO has the best efficiency and that this advantage is most pronounced for narrow detectors.