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

A new method for processing signals from Anger position-sensitive detectors used in gamma cameras and PET (Positron Emission Tomography) is proposed for very high count-rate imaging. It has a same concept as HYPER (High Yield Pileup-Event Recover) method we introduced before [1-2] by using (a) dynamically integrating a present event, the integrating will stop immediately before the next event is detected; (b) estimating a weighted-value to indicate the total energy inside the scintillation detector; and (c) 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 is applying 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 described the application of the improved HYPER electronics to a high resolution low cost PET camera with 12 PQS (PMT-quadrant-sharing) detector modules that can decode 38,016 BGO crystal elements using 924 PMTs. Each detector module has 4 HYPER circuits to further increase the count-rate. To use the HYPER circuit in coincidence imaging application, there is a serious synchronization problem between the arrival time of an event and the end of integration that is variable from event to event. This synchronization problem is solved by a FPGA circuit with real time remnant correction and a high-resolution trigger delay unit with small dead-time for recovering the synchronization of data and event-trigger.