National Electrical Manufacturers Association (NEMA) NU 2-2007 performance measurements were conducted on the Inveon ™ preclinical small animal PET system developed by Siemens Medical Solutions. The scanner uses 1.51 × 1.51 × 10 mm LSO crystals grouped in 20 × 20 blocks; a tapered light guide couples the LSO crystals of a block to a position-sensitive photomultiplier tube. There are 80 rings with 320 crystals per ring and the ring diameter is 161 mm. The transaxial and axial fields of view (FOVs) are 100 and 127 mm, respectively. The scanner can be docked to a CT scanner; the performance characteristics of the CT component are not included herein. Performance measurements of spatial resolution, sensitivity, scatter fraction and count rate performance were obtained for different energy windows and coincidence timing window widths. For brevity, the results described here are for an energy window of 350-650 keV and a coincidence timing window of 3.43 ns. The spatial resolution at the center of the transaxial and axial FOVs was 1.56, 1.62 and 2.12 mm in the tangential, radial and axial directions, respectively, and the system sensitivity was 36.2 cps kBq −1 for a line source (7.2% for a point source). For mouse-and rat-sized phantoms, the scatter fraction was 5.7% and 14.6%, respectively. The peak noise equivalent count rate with a noisy randoms estimate was 1475 kcps at 130 MBq for the mouse-sized phantom and 583 kcps at 74 MBq for the rat-sized phantom. The performance measurements indicate that the Inveon ™ PET scanner is a high-resolution tomograph with excellent sensitivity that is capable of imaging at a high count rate.

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A flexible, extensible, high-speed architecture, called QuickSilver TM and specifically geared to the requirements of small animal imaging, has been developed. The architecture is composed of ring-based event processing modules (EPMs) with nearest neighbor, high-speed digital communication transmitting event packets via a "store and forward" concept. Each EPM is capable of transmitting up to 15.6M events/sec to other EPMs. Coincidence determination is performed at the EPM level around the "ring". This distributes the load and eliminates the need for a separate coincidence processor. Each EPM is capable of transmitting up to 1.9M coincidence events/sec to an event routing subsystem (ERS) for acquisition and processing. The ERS has 2 transport interfaces for acquiring events: an IEEE 1394A interface and a PCI interface. The IEEE 1394A interface can support up to 5.3M events/sec and the PCI interface can support up to 16.7M events/sec. Thus this architecture provides a new level of capability for small animal PET imaging, but is also extremely well suited for PET research, single photon emission computed tomography (SPECT) imaging, and use with X-ray CT and magnetic resonance imaging (MRI).

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