Depth of interaction in the scintillation camera: stochastic and geometric effects

The stochastic nature of the DOI (depth of interaction) and its influence on various imaging parameters is described. Specific effects of the DOI on the PM (photomultiplier) response of gamma cameras have been quantified. In a typical camera configuration and 140-keV photons, the DOI alone can account for a 6.4-mm discrepancy in position and 12% in energy between two scintillations. Variation of the DOI can still bring additional distortions when photons do not enter the crystal perpendicularly, as in slant hole, cone beam, and other focusing collimators. With a 0.95-cm crystal and a 30 degrees slant angle, the obliquity factor can be responsible for a 5.5-mm variation in the event position. Results indicate that both geometrical and stochastic effects of the DOI are definitely reducing the camera performances and should be included in the image formation process.<>