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.
A multi-purpose readout electronics based on the DPLMS digital filter has been developed for CdTe and CZT detectors for X-ray imaging applications. Different filter coefficients can be synthesized optimized either for high energy resolution at relatively low counting rate or for high rate photon-counting with reduced energy resolution. The effects of signal width constraints, sampling rate and length were numerical studied by Mento Carlo simulation with simple CRRC shaper input signals. The signal width constraint had minor effect and the ENC was only increased by 6.5% when the signal width was shortened down to 2 τc. The sampling rate and length depended on the characteristic time constants of both input and output signals. For simple CR-RC input signals, the minimum number of the filter coefficients was 12 with 10% increase in ENC when the output time constant was close to the input shaping time. A prototype readout electronics was developed for demonstration, using a previously designed analog front ASIC and a commercial ADC card. Two different DPLMS filters were successfully synthesized and applied for high resolution and high counting rate applications respectively. The readout electronics was also tested with a linear array CdTe detector. The energy resolutions of Am-241 59.5 keV peak were measured to be 6.41% in FWHM for the high resolution filter and to be 13.58% in FWHM for the high counting rate filter with 160 ns signal width constraint.