A new pileup-prevention front-end electronic design for high-resolution PET and gamma cameras

Abstract

A new method for processing signals from Anger position-sensitive detectors used in gamma cameras and positron emission tomography (PET) is proposed for very high count-rate imaging. It has a same concept as high yield pileup-event recover (HYPER) method we introduced before by using 1) dynamically integrating a present event, the integrating will stop immediately before the next event is detected; 2) estimating a weighted-value to indicate the total energy inside the scintillation detector; and 3) remnant correction to remove the residual energy of all the previous events from the weighted-value. This paper introduces two improved practical techniques to get a better weighted-value with low noise sensitivity in order to improve the final pileup-free energy resolution. One applies a low-pass filter combined with multiple sampling to a weight-sum of the instantaneous signal and integrated signal. The other one is weighting the integration value of the income signal; the weighting also includes exponential distortion compensation. This paper also describes the application of the HYPER electronics in a high resolution low cost PET camera with 12 photomultipliers (PMTs)-quadrant-sharing (PQS) detector modules that can decode 38 016 bismuth-germinate (BGO) crystal elements using 924 PMTs. Each detector module has four Anger-HYPER circuits to further increase the count-rate. To use the HYPER circuit in coincidence imaging applications, there is a serious synchronization problem between the arrival time of an event and the end time of integration that is variable from event to event. This synchronization problem is solved by a field programmable gate array (FPGA) circuit with real time remnant correction and a high-resolution trigger delay unit with a small dead-time for recovering the synchronization of data and the event-trigger.