Imaging performance of the 2nd generation RatCAP PET scanner

Abstract

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Objectives: The first-generation RatCAP has been used to image phantoms and rat brains using multiple tracers: F-18 FDG, C-11 raclopride, C-11 methamphetamine, and F-18 fluoride. The results have been encouraging on a qualitative level, but a 2nd generation of the RatCAP has been developed to improve physical corrections, sensitivity, time resolution, and flexibility of operation. Methods: A large effort has been devoted to correcting for physical effects by implementing novel strategies which take advantage of the unique properties of the RatCAP. Specifically, corrections have been developed for detector efficiency normalization, coincidence timing offsets, randoms, scatter, and attenuation. In addition, to reduce the statistical noise in the images and streamline the data acquisition, all the hardware components are being upgraded into a 2nd generation design. The LSO scintillators are 2 mm longer giving an approximate factor of 2 increase in coincidence sensitivity but only a minimal increase in size and weight. A new front-end electronic microchip (ASIC) has been designed and fabricated with lower noise and new features including variable gain, thereby improving the time resolution. The chip now sends data to an upgraded time stamp and signal processing module (TSPM) in a more robust differential mode, and the TSPM communicates via optical fibers to a compact PCI card in a standard PC. In parallel, a focus on new approaches to animal behavioral training is expected to soon yield conscious rat brain images. Results: Image quantitation is validated with phantom data under varying conditions of activity and attenuating media. Time resolution and coincidence sensitivity improvements suggest improved noise performance, which is verified with noise equivalent count rate (NECR) measurements. Conclusions: Significantly improved quantitative performance has been enabled with the 2nd generation RatCAP design.

Research Support (if any): DOE OBER funding