A simple and improved digital timing method for positron emission tomography

A simple and improved digital timing method has been developed for positron emission tomography (PET). The so-called initial rise interpolation method is based on an important characteristic of gamma signal: a properly pre-amplified and sampled gamma signal pulse can be characterized to arrive with an initial rise from baseline and then to go up with a maximum rise. Pulse arrival time is obtained by calculating the intersection of the initial rise line with the baseline for each gamma signal pulse. In this study, a FPGA-based data acquisition (DAQ) card was used for data acquisition and processing. We measured coincidence timing resolution of two types (fast and slow) of recently developed 3 mm × 3 mm Geiger mode avalanche photodiodes (GAPDs) using 3 different digital timing methods: initial rise interpolation (IRI), digital CFD and maximum rise interpolation (MRI). Furthermore, simulation has been performed to evaluate effects of pulse rise time, pulse amplitude and front-end noise level on timing resolution estimated by the three digital timing methods. Measured results show that, IRI method provided the best timing resolution for both types of GAPDs: 0.7 ns FWHM for fast GAPD and 1.5 ns for slow GAPD (digital CFD: 1.5 ns and 2.2 ns; MRI: 1.8 ns and 2.7 ns). In accordance with measured results, simulation results also show that IRI method provided the best timing resolution. Based on these experimental results, we concluded that the developed simple and improved digital timing method is reliable and useful for the development of high performance PET.