Maximum likelihood positioning in the scintillation camera using depth of interaction

The depth of interaction (DOI) in the scintillation crystal of a gamma camera is modifying the response of each photomultiplier, therefore introducing imprecision in the evaluation of both event energy and position. To compensate for these errors, an iterative 3-D maximum likelihood positioning algorithm (x, y, and DOI) was developed. An analytical calculation of the exact solid angle function yields the DOI, which is used to reevaluate the event energy, thus compensating for that portion of light which die not attain the photodetectors. The method was tested on a Monte Carlo simulator, with special attention given to noise modeling. Two models were developed, the first considering only the geometric aspects of the camera and used for comparison, and the second describing a more realistic camera environment. Different signal-to-noise ratios were used to test the algorithm. As an indication of the performance, quasi-perfect positioning was achieved with the technique using the geometric model while the 2-D approach still produces close to 1-mm deviation in some points. Energy evaluation is greatly improved, offering a way to stabilize camera performance over the entire energy spectrum.<>