Optimizing timing performance of silicon photomultiplier-based scintillation detectors

Abstract

Precise timing resolution is crucial for applications requiring photon time-of-flight (ToF) information such as ToF positron emission tomography (PET). Silicon photomultipliers (SiPM) for PET, with their high output capacitance, are known to require custom preamplifiers to optimize timing performance. In this paper, we describe simple alternative front-end electronics based on a commercial low-noise RF preamplifier and methods that have been implemented to achieve excellent timing resolution. Two radiation detectors with L(Y)SO scintillators coupled to Hamamatsu SiPMs (MPPC S10362–33-050C) and front-end electronics based on an RF amplifier (MAR-3SM+), typically used for wireless applications that require minimal additional circuitry, have been fabricated. These detectors were used to detect annihilation photons from a Ge-68 source and the output signals were subsequently digitized by a high speed oscilloscope for offline processing. A coincident resolving time (CRT) of 147 ± 3 ps FWHM and 186 ± 3 ps FWHM with 3 × 3 × 5 mm3 and with 3 × 3 × 20 mm3 LYSO crystal elements were measured, respectively. With smaller 2 × 2 × 3 mm3 LSO crystals, a CRT of 125 ± 2 ps FWHM was achieved with slight improvement to 121 ± 3 ps at a lower temperature (15°C). Finally, with the 20 mm length crystals, a degradation of timing resolution was observed for annihilation photon interactions that occur close to the photosensor compared to shallow depth-of-interaction (DOI). We conclude that commercial RF amplifiers optimized for noise, besides their ease of use, can produce excellent timing resolution comparable to best reported values acquired with custom readout electronics. On the other hand, as timing performance degrades with increasing photon DOI, a head-on detector configuration will produce better CRT than a side-irradiated setup for longer crystals.

A Time-Walk Correction Method for PET Detectors Based on Leading Edge Discriminators

“…Better results have been obtained with similar SiPMs and crystals, however we did not optimize the bias voltage for timing performance and our measurement were carried out at a temperature of 20 ° C. For SiPMs, the timing resolution varies with bias voltage and better timing resolution can be obtained at lower temperature, as the noise of SiPMs is decreased [28]–[29]. …”

The lower timing resolution bound for scintillators with non-negligible optical photon transport time in time-of-flight PET

“…The crystal is read out with a Hamamatsu S10362-33-50C SiPM. See [Yeom et al, 2013] for more details on the crystal geometry.…”

“…For these simulations, an index of refraction of n = 1:82 was chosen for the LYSO:Ce crystal. All crystal faces were chosen to be polished (as for the crystal in [Yeom et al, 2013]). The reflective surface on the 4 crystal side faces was chosen to exhibit specular (mirror-like) reflectance, as is the case for the 3M ESR reflector.…”

“…with a constant distance to the SiPM and thus constant excitation depth. This allowed the evaluation of the timing resolution bound as a function of the excitation depth, to facilitate a comparison with that experimentally measured in [Yeom et al, 2013]. …”

“…Recently, it has been shown that excellent coincident resolving times (CRTs) below 200 ps FWHM can be achieved with LYSO:Ce and LaBr 3 :Ce scintillation crystals coupled to silicon photomultipliers (SiPMs) (e.g. [Yeom et al, 2013, Schaart et al, 2010, Gundacker et al, 2014]). These CRTs were typically achieved with specialized acquisition setups (e.g.…”