Time Determination of BGO-APD Detectors by Digital Signal Processing for Positron Emission Tomography (original) (raw)

2009, IEEE Transactions on Nuclear Science

Coincidence timing resolution in Positron Emission Tomography (PET) can be improved by replacing fast analog pulse shaping and Constant Fraction Discriminator (CFD) with fully digital signal processing. This can be achieved by digitizing the signal from individual detectors using 100-MHz, 8-bit Analog-to-Digital converters (ADC) and by processing the data on-the-fly in Field Programmable Gate Arrays (FPGA). Various digital filters and baseline restorers were implemented and combined with numerical least mean square fit to the data to extract the time of interaction and the energy deposited in BGO-APD detectors. An intrinsic time resolution of 7.2 ns was obtained with digital techniques. However, it is shown that bias in the timestamp estimation can be introduced by digital time discrimination techniques, which could affect the ability of digital methods to accurately estimate random event rates by the delayed time window method. Accordingly, the coincidence FWHM metric should not be the only figure of merit when comparing digital and analog time discrimination strategies. Index Terms-Avalanche photodiodes, digital circuits, digital signal processing, field-programmable gate arrays (FPGAs), numerical methods, PET, time resolution. I. INTRODUCTION T HE EVER increasing use of small animal models in PET imaging requires improvement of spatial resolution, reduction of parallax error by depth-of-interaction measurement in detectors, and more accurate selection of useful events to improve image quality [1], [2]. A related goal would be the ability to reconfigure system parameters according to the imaging protocol. In another respect, it could be advantageous to be able to adapt the system to the novel scintillation detectors that are becoming available, rather than redesign the front-end processing Manuscript

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