Automatic Threshold Calibration for MVT-Based All Digital PET

Abstract

The multi-voltage threshold (MVT) method is an all digital scintillation pulse sampling method that has shown many advantages over the traditional analog-digital mixed approach in positron emission tomography (PET). Several preclinical, clinical and application specific digital PET systems have been built based on the all digital PET detectors. We have developed the threshold calibration method for MVT that is implemented in the production of detectors. In this paper, we propose an automatic threshold calibration (ATC) method. Based on the accurate direct current (DC) reference bias voltage applied to the pulse signal, the threshold is automatically calibrated using the difference between the reference and the output of the digital-to-analog converter (DAC) that causes the comparator to flip. The evaluation results show that the ATC method has comparable performance to the previous method. The ATC method is suitable for the threshold calibration in the situation of large-scale integration of the MVT channels, as well as time-driven pulse sampling method. More importantly, no hardware changes are required and only firmware updates of the PET detector are needed for implementation the method, which demonstrate the advantages of the flexibility and scalability of all-digital PET. All-digital PET also has potentials for automatic calibration of energy and time, which are being investigated.