An investigation of waveform sampling for improved signal processing in TOF PET

The development of fast photodetectors and of fast, high light output scintillation crystals has placed an increased emphasis on the need for fast readout electronics used for Time-Of-Flight (TOF) PET detectors. These improvements have paralleled developments in analog sampling technology that makes fast waveform digitizing of photodetector signals an attractive alternative to custom PCB and IC designs. Waveform digitization offers a flexible means for evaluating and implementing more complex signal processing algorithms. We used a commercial 1GHz 2Gs/s waveform digitizing system to acquire coincident pulses from LYSO and LaBr3 (5%Ce) scintillator crystals coupled to a fast PMT. By measuring the time pickoff based on a linear fit to the rising edge of the pulse, we show an improvement in coincident timing resolution from ∼200ps to ∼80ps FWHM for LaBr3(5%Ce) coupled to Photonis XP20D0 PMTs, and from ∼160ps to ∼80ps Full Width at Half Maximum (FWHM) for LaBr3(5%Ce) coupled to Hamamatsu H4998 PMTs. Our results show a consistent improvement in timing resolution as well as reduced sensitivity to signal risetime as compared to leading edge (LE) pickoff techniques. Measurements with partial detector modules indicate that system timing resolution of ≪200ps is attainable with LaBr3 (5%Ce) pixelated detectors designed for TOF PET.