Flood Histogram Quality Metric for Light Sharing Depth-encoding PET Modules

Spatial performance of single-ended readout depth-encoding PET modules with multicrystal scintillator arrays that are n-to-1 coupled to readout pixels relies on the ability to identify the crystal where each gamma ray is absorbed based on light sharing patterns. Energy weighted average method is the most popular method for performing crystal identification in such detector modules. However, quantitative metrics that characterize flood histogram quality haven't yet been developed for this practical, cost-effective detector module configuration. In this work, we introduce a flood histogram quality metric that determines how well-separated the crystal identification clusters are when coupling multiple crystals to the same readout pixel. We compare the flood histogram quality between 4-to-1 coupled modules with a standard uniform glass light guide and our newly developed prismatoid light guide array, which is used in Prism-PET detector module configurations. Both modules consisted of 16 × 16 arrays of 1.4 × 1.4 × 20 mm³ LYSO crystals coupled 4-to-1 to 3.2 × 3.2 mm² SiPM pixels. The Prism-PET module exhibited 40% better flood histogram quality than the uniform light guide module. Crystal clusters acquired at 5 different depths in both modules demonstrated how Prism-PET increases the depth-dependence of crystal contours, thus enhancing crystal separation. Our flood histogram quality metric is a quantitative measure that helps characterize high resolution single-ended readout modules with n-to-1 crystal-to-readout coupling.