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 /spl gamma/-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 /spl sigma/ of the light distribution can be computed, providing a good estimator for the depth of interaction (DOI). We measured the /spl sigma/ resolution at 81 positions of a test-detector's sensitive area and found an average resolution of 6/spl plusmn/4.0 mm. At the central region of 20/spl times/20 mm/sup 2/ the performance of our method was with 3/spl plusmn/0.8 mm /spl sigma/ resolution much better. The lowest observed value was 1.8 mm. The 0th, 1st/sub X/, 1st/sub 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.

I. Introduction

A major problem in positron emission tomographic imaging is the parallax error caused by the necessarily thick scintillator crystals when no depth of interaction (DOI) information is provided. It leads to event mispositioning and degrades spatial resolution for points located at large radial distances from the scanner's central axis [1]. For existing -ray imaging systems, the image quality can be improved potentially, when sufficiently good estimates for the DOI is provided by the detector [2], [3]. While other effects, for instance, mispositioning due to Compton scattering inside the scintillator, a finite positron travelling path and residual non-collinearity of the annihilation radiation, contribute uniformly to the resolution degradation, the lack of DOI leads to radial resolution loss.