A digital deconvolution method with pile-up reconstruction has been proposed for scintillator detectors for high rate photon-counting X-ray imaging applications. The detector signal was modeled as an exponential decay waveform convoluted with the single photon response of the SiPM detector. An impulse signal can be obtained by digital deconvolution (unfolding) with much shorter duration, which was then used for energy estimation followed by a trapezoid filter and pile-up discrimination. The whole digital deconvolution algorithm has been synthesized and verified by both SIMULINK simulation and experimental tests. The prototype of the detector and the readout electronics were developed for demonstration, using 3 mm x 3 mm x 10 mm LYSO scintillator coupled with a 3 mm x 3 mm SenSL SiPM. A 14 bit, 100 MSPS ADC was used to sample the analog waveform and the digital filter was implemented in a Xilinx Kintex 7 FPGA. The signal width was shortened from ~250 ns to 10~20 ns and then was shaped into trapezoidal pulse with 100 ns width. The energy was estimated from the trapezoid top for better signal collection and noise rejection. The unfolded pulses were used for pile-up discrimination and to reconstruct two pile-up signals from the overlapped trapezoid outputs. The energy performance of the prototype system was firstly validated by measuring the energy spectrums of ²⁴¹Am, ⁵⁷Co, ²²Na and ¹³⁷Cs radiation sources. The energy resolutions were measured to be 36.9%, 29.9%, 13.9% and 12.9% respectively at 59.5 keV, 122 keV, 511 keV and 662 keV in FWHM. High rate performance was evaluated by an X-ray generator. The maximum output counting rate was measured to 5.36 Mcps without saturation, comparing with the saturated counting rate of 2.34 Mcps using the original LYSO signals. The saturation counting rate using digital deconvolution was estimated to be up to ~7 Mcps fitted with the paralyzable dead time model, corresponding to ~20 Mcps input count rate.

Date Published: 13 September 2018
PDF: 13 pages
Proc. SPIE 10762, Hard X-Ray, Gamma-Ray, and Neutron Detector Physics XX, 107620A (13 September 2018); doi: 10.1117/12.2320425

Published in SPIE Proceedings Vol. 10762:
Hard X-Ray, Gamma-Ray, and Neutron Detector Physics XX
Stephen A. Payne; Ralph B. James; Arnold Burger; Michael Fiederle, Editor(s)