Energy and timing measurement of a PET detector with time-based readout electronics

Abstract

New time-based readout (TBR) electronics has been developed and evaluated for its performance and application for PET detectors. It consists of a leading edge (LE) timing threshold for timing pickoff that provides a signal timing t1; a charge integration followed by a constant discharge between two specific timings t2 and t3 that are used to directly measure the signal energy. The timing-walk error caused by LE from signals of different amplitudes can be measured with t1 as a function of different signal amplitudes that is proportional to the time difference between t2 and t3. With this pre-calibration, timing-walk error can be accurately corrected. Therefore, both signal timing and energy can be accurately measured with digital timing signals without using CFD and ADC. These timing signals were controlled and in principle can be measured by an FPGA that can apply many signal logic and data correction algorithms. A single channel discrete component TBR circuit has been implemented in PC board, and 8-channel ASIC chips have been developed for feasibility evaluations and PET detector applications. Initial functionality and performance evaluations have been conducted. Signal amplitude measurement accuracy and linearity are very good; the measured timing accuracy from a pulse is the same as a standard CFD and reaches to ∼100 ps resolution with the test setup. Both suitable energy and coincidence timing resolutions (∼17% and ∼1.0–2.0 ns) were achieved with PMT or Solid-State PM (SSPM) array based PET detectors. Initial studies to acquire flood source crystal identification map has demonstrated the advantages of applying parallel readout with TBR electronics that read out and process signals from each pixel of SSPM array independently. With its relatively simple circuit and low cost, TBR electronics is expected to provide suitable front-end signal readout electronics for compact photon detectors such as SSPM array that require large number of output channels and demand high performance in energy and timing.