Signal deconvolution concept combined with Cubic Spline interpolation to improve timing with phoswich pet detectors

PET imaging scanners based on all-digital architecture offer greater data processing flexibility and the possibility to recalibrate the system with simple software procedures. The LabPET™ scanner, designed at the Université de Sherbrooke, is one such device. It is built around dual LYSO/LGSO scintillators in a phoswich arrangement coupled to Avalanche Photodiodes (APD)and combined with highly parallel readout and processing electronics. This approach enables the implementation of advanced real time digital signal processing methods to compute energy resolution, crystal identification and the arrival time of events. Timing extraction represents the highest challenge because of the low sampling frequency (45 MHz), the quantization error and the presence of a Zero Order Hold (ZOH) in the system. The aim of this paper is to present a method to increase coincidence time accuracy by adequately addressing each of these limitations. The proposed method uses a Deconvolution concept based on adaptive filter theory preceded by Cubic Spline interpolation to improve digital timing performance. The method achieves 4.5 ns, 8.2 ns and 6.5 ns timing resolution with, LYSO-LYSO, LGSO-LGSO and mixed crystals phoswich coincidences, respectively.