Spectral-Spatial-Sensitivity Distortion Trends and an Accurate Correction Method in Scintillation Gamma Cameras

The discrete nature of PMT's in the Anger camera results in image distortion through the variations of photopeak amplitude and spread, spatial misregistration and resolution, and pixel size variation. Each distortion has been examined by both computer simulation and experimentation. A method aligning the photopeak centroids over the camera face has been developed by applying local gain factors, obtained via statistical stabilization between two equal bins set around the raw camera photopeak. The energy resolution has improved from 13 to 10% for 140 keV gammas with a 128 × 128 pixel matrix. A new spatial linearity correction algorithm measures the X and Y distortions at a matrix of orthogonal points. A 128 × 128 linearity correction matrix is generated through expansion by 2-D Lagrangian polynomial interpolation and transformation into uncorrected coordinates. Typical absolute linearity in the camera CFOV is under 0.3 mm. Even with these corrections, a sensitivity uniformity correction is needed to maintain the 1 to 2% uniformity required for SPECT. An X and Y mechanical registration alignment corrects for angular dependent shift in both camera axes.