Performance evaluation of microPET: A high-resolution lutetium oxyorthosilicate PET scanner for animal imaging

A new dedicated PET scanner, microPET, was designed and developed at the Un iversity of California, Los Angeles, for imaging small laboratory animals. The goal was to provide a compact system with superior spatial resolution a t a fraction of the cost of a clinical PFT scanner. Methods: The system use s fiberoptic readout of individually cut lutetium oxyorthosilicate (LSO) cr ystals to achieve high spatial resolution. Each microPET detector consists of an 8 X 8 array of 2 x 2 x 10-mm LSO scintillation crystals that are coup led to a 64-channel photomultiplier tube by optical fibers. The tomograph c onsists of 30 detectors in a continuous ring with a 17.2-cm diameter and fi elds of view (FOVs) of 11.25 cm in the transaxial direction and 1.8 cm in t he axial direction. The system has eight crystal rings and no interplane se pta. It operates exclusively in the three-dimensional mode and has an elect ronically controlled bed that is capable of wobbling with a radius of 300 m u m. We describe the performance of the tomograph in terms of its spatial, energy and timing resolution, as well as its sensitivity and counting-rate performance. We also illustrate its overall imaging performance with phanto m and animal studies that demonstrate the potential applications of this de vice to biomedical research. Results: Images reconstructed with three-dimen sional filtered backprojection show a spatial resolution of 1.8 mm at the c enter of the FOV (CFOV), which remains <2.5 mm for the central 5 cm of the transaxial FOV. The resulting volumetric resolution of the system is <8 mu L. The absolute system sensitivity measured with a 0.74 MBq (20 mu Ci) Ge-6 8 point source at the CFOV is 5.62 Hz/kBq. The maximum noise equivalent cou nting rate obtained with a 6.4-cm diameter cylinder spanning the central 56 % of the FOV is 10 kcps, whereas the scatter fraction is 37% at the CFOV fo r an energy window of 250-650 keV and the same diameter cylinder. Conclusio n: This is the first PET scanner to use the new scintillator LSO and uses a novel detector design to achieve high volumetric spatial resolution. The c ombination of imaging characteristics of this prototype system (resolution, sensitivity, counting rate performance and scatter fraction) opens up new possibilities in the study of animal models with PET.