A low dead time full digital Pulse-Shape-Discriminator (PSD) for DOI PET

Pulse-shape-discriminator (PSD) has been used for the last 40 years in radiation detection systems ranging from medical diagnostic imaging cameras to high energy physics. The function of PSD is to differentiate radiation signals based on different signal shape. It can be used to identify the scintillator type in (Depth of interaction) DOI PET application, where the detector is divided into two or more layers, with each layer using a different type of scintillator (with different decay constant). In this work, a new PSD method is introduced. The method is based on our digital high-yield-pileup-event-reeover (HYPER) method, a dynamic integration and remnant correction method which is mainly used for pile-up correction. In this method, the input signal is first digitized with ADC, and then weight-summed inside FPGA. The weight factor is decided by the scintillation decay time. Suppose we use the weight factor of one decay time, the weight-sum result of this crystal will be flat, and then the HYPER result of crystal with other decay time is not flat. By judging if the weight-sum result is flat, we can identify the type of the crystal. This method is tested using a LSO crystal with decay time of 40ns and a GSO with decay time of 100ns. More than 95% of the events can be correctly judged with dead-time of about 60ns.