DOI-enhanced gamma-ray position detection for a small animal PET camera

We studied the possibility of correcting edge artifacts caused by the center of gravity positioning algorithm (COG) within thick continuous scintillation crystals for γ-ray imaging detectors. An enhanced charge division readout (CDR) together with multi-channel position sensitive photo-multiplier tubes allows the measurement of the 2nd moment of the scintillation light distribution within continuous and large-sized crystals. Using the 2nd moment together with the centroids provided by the CDR, the standard deviation σ of the light distribution can be computed, providing a good estimator for the depth of interaction (DOI). We measured the σ resolution at 81 positions of a test-detector´s sensitive area and found an average resolution of 6±4.0 mm. At the central region of 20×20 mm² the performance of our method was with 3±0.8 mm σ resolution much better. The lowest observed value was 1.8 mm. The 0th, 1st_X, 1st_Y and 2nd moments of the light distribution were also measured for the 81 positions and compared to predictions obtained by a model for the light distribution. Analytic studies show that the use of the first low order moments probably allows significant reduction of the DOI-caused border artifacts of the COG algorithm.