Maximum likelihood positioning in the scintillation camera using depth of interaction.

Specific effects of the depth of interaction (DOI) on the photomultiplier (PM) response in an Auger gamma camera were quantified. The method was implemented and tested on a Monte Carlo simulator with special care to the noise modeling. Two models were developed, one considering only the geometric aspects of the camera and used for comparison, and one describing a more realistic camera environment. 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 such 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.