Measure PET detector performance with the intrinsic radioactivity of scintillator

One common configuration of PET detector modules is an array of scintillators, usually LYSO or its variant, coupled to multiple photomultiplier tubes (PMTs). The objective of this work was to test the feasibility of measuring the performance of such detector module with the intrinsic radioactivity from the ¹⁷⁶Lu in the scintillator for its convenience and uniformity. The performance indices of a detector module include the individual crystal energy resolution and relative crystal light collection efficiency. They are indispensable in detector and system development. As no prominent photoelectric-peak exists in the ¹⁷⁶Lu energy spectrum, it is not straight forward to obtain the detector performance indices from the acquired data. We developed a method to derive the crystal energy resolution and the relative crystal light collection efficiency by fitting the experiment crystal energy spectrum with simulated crystal energy spectrum. The detector module of this study consisted of a 6 by 6 L YSO scintillator array coupled to 4 PMTs. A 2-minute and a 30-minute two dimensional position map (2Dmap) were acquired for evaluating data with short and long scans. With the short acquisition data, we can generally evaluate the performance of the detector. With the long acquisition data, we segmented the 2Dmap and obtained the crystal energy resolutions to be 25% to 45% and the relative crystal light collection efficiency to be 0.43 to 1. We concluded that the ¹⁷⁶Lu background radiation could be used to evaluate LYSO and its variant based PET detector module.