Coincidence measurements on detectors for microPET II: a 1 mm3 resolution PET scanner for small animal imaging

Summary form only received as follows: The authors are currently developing a small animal PET scanner with a design goal of 1 mm³ image resolution. They have built 3 pairs of detectors and tested performance in terms of crystal identification, spatial, energy and timing resolution. The detectors consisted of 12×12 arrays of 1×1×10 mm LSO crystals (1.15 mm pitch) coupled to Hamamatsu H7546 64 channel PMTs via 5 cm long coherent glass fiber bundles. Optical fiber connection is necessary to allow high packing fraction in a ring geometry scanner. Fiber bundles with and without extramural absorber (EMA) were tested. The results demonstrated an intrinsic spatial resolution of 1.12 mm (direct coupled LSO array), 1.23 mm (bundle without EMA) and 1.27 mm (bundle with EMA) using a -500 micron diameter Na-22 source. Using a 330 micron line source filled with F-18, intrinsic resolution for the EMA bundle improved to 1.05 mm. The respective timing and energy resolution values were 1.96 ns, 21% (direct coupled), 2.20 ns, 23% (bundle without EMA) and 2.99 ns, 30% (bundle with EMA). Peak-to-valley ratio in the flood histograms was better with EMA (5:1) compared to the bundle without EMA (2.1:1). These detectors substantially improve on the performance characteristics of the detectors in the authors´ current microPET scanner