Optimal scintillation time estimation through analog filters
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Date
2023
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Abstract
Scintillator crystals are a widespread solution for detecting high-energy radiation. These crystals spread the energy of the particle over time, which fundamentally limits the time resolution that can be obtained. This is relevant for applications requiring good time resolution, such as ToF-PET, which is currently aiming at resolutions in the order tens of picoseconds, and low energy measurements, where the limit is further degraded. The most common approach to measure scintillation time is leading-edge discrimination (LED), which performs better than other time measurement techniques because of the high variability of the measured waveforms, while more complex approaches using digital signal processing only present small improvements. In this work, an alternative detection technique is presented, by showing that a multi-variate MLE, which considers the shape and amplitude of the distribution, can be performed by feeding the output current of a SiPM to a filter, whose output is proportional to the log-probability of the scintillation time under a given distribution. It is shown that said filter can be implemented as an analog, passive pulse-shaper on a typical SiPM readout front-end, and the optimal estimation is made by evaluating a combined estimator of the time and amplitude of the maximum of the response. It is shown through a custom simulation that the proposed method gives an estimate independent of both energy and waveform variations, but has a slightly reduced resolution with respect to LED, so its convenience should be tested for each particular application.
Description
Tesis (Master of Science in Engineering)--Pontificia Universidad Católica de Chile, 2023
Keywords
Scintillator, ToF-PET, CFD, Time measurement, Time estimation, Maximum likelihood, Bias correction, Adapted filter, Analog filter