How the polychromatic retrigger can increase the count-rate capabilities of photon-counting detectors

High photon fluxes, like the ones required in clinical computed tomography, could generate pulse pileup in photon-counting detectors, and in extreme cases induce paralysis. The instant retrigger by DECTRIS Ltd. is a technology developed to face such scenarios and to counteract detector paralysis. In this work, we present how the instant retrigger can be tuned for each specific energy threshold (polychromatic retrigger) in order to increase the maximum detectable count rate. Using a Monte Carlo method, we simulated count rates from 1 Mcps/mm² to 10’000 Mcps/mm², for four energy thresholds at 20, 50, 70, and 90 keV. The results show that it is possible to optimize the retrigger time for each threshold, reducing it up to 20 ns for the highest threshold without double counting, and thus providing detected count rates up to 500 Mcps/mm². This value is 3 times higher than what is achievable with a single retrigger time for all thresholds. Furthermore, we show how the polychromatic retrigger can be optimized in the case where the pulse pileup has to be minimized. All the proposed methods rely on specific hardware, capable of simultaneously setting different retrigger times for different energy thresholds. Such hardware is currently under development at DECTRIS Ltd.