UniMIB, Piazza dell'Ateneo Nuovo, 1-20126, Milano, Italy. CERN, 1211 Geneve 23, Switzerland.
Phys Med Biol. 2019 Feb 27;64(5):055012. doi: 10.1088/1361-6560/aafd52.
Scintillator based radiation detectors readout by SiPMs successively break records in their reached time resolution. Nevertheless, new challenges in time of flight positron emission tomography (TOF-PET) and high energy physics are setting unmatched goals in the 10 ps range. Recently it was shown that high frequency (HF) readout of SiPMs significantly improves the measured single photon time resolution (SPTR), allowing to evaluate the intrinsic performance of large area devices; e.g. FBK NUV-HD SiPMs of [Formula: see text] mm area and 40 [Formula: see text]m single photon avalanche diode (SPAD) size achieve 90 ps FWHM. In TOF-PET such readout allows to lower the leading edge detection threshold, so that the fastest photons produced in the crystal can be utilized. This is of utmost importance if a high SPTR and prompt Cherenkov light generated by the hot-recoil electron upon 511 keV photo-absorption should improve timing. This paper shows that high-frequency bipolar transistor readout of state-of-the-art SiPMs coupled to high-performance scintillators can substantially improve the best achievable coincidence time resolution (CTR) in TOF-PET. In this context a CTR of 158 [Formula: see text] 3 ps FWHM with [Formula: see text] mm BGO crystals coupled to FBK SiPMs is achieved. This faint Cherenkov signal is as well present in standard LSO scintillators, which together with low SPTR values (<90 ps FWHM) improves the CTR of [Formula: see text] mm LSO:Ce:Ca coupled to FBK NUV-HD [Formula: see text] mm with 25 [Formula: see text]m SPAD size to 61 [Formula: see text] 2 ps FWHM using HF-electronics, as compared to 73 [Formula: see text] 2 ps when readout by the NINO front-end ASIC. When coupling the LSO:Ce:Ca crystals to FBK NUV-HD SiPMs of [Formula: see text] mm and 40 [Formula: see text]m SPAD size, using HF-electronics, a CTR of even 58 [Formula: see text] 3 ps for [Formula: see text] mm and 98 [Formula: see text] 3 ps for [Formula: see text] mm is achieved. This new experimental data will allow to further discuss the timing limits in scintillator-based detectors.
基于闪烁体的辐射探测器通过 SiPM 相继在时间分辨率方面创下纪录。然而，在飞行时间正电子发射断层扫描（TOF-PET）和高能物理领域的新挑战正在设定无与伦比的 10 ps 范围内的目标。最近表明，SiPM 的高频（HF）读出显著提高了测量的单光子时间分辨率（SPTR），从而可以评估大面积器件的固有性能；例如，FBK NUV-HD SiPM 的面积为[Formula: see text]mm，单个光子雪崩二极管（SPAD）尺寸为 40 [Formula: see text]m，可实现 90 ps FWHM。在 TOF-PET 中，这种读出允许降低前沿检测阈值，从而可以利用在晶体中产生的最快光子。如果要提高时间分辨率并利用由 511 keV 光吸收产生的热反冲电子产生的快速切伦科夫光，则这一点至关重要。本文表明，与高性能闪烁体耦合的最先进的 SiPM 的高频双极晶体管读出可以大大提高 TOF-PET 中可实现的最佳符合时间分辨率（CTR）。在此背景下，使用[Formula: see text]mm BGO 晶体与 FBK SiPM 耦合，实现了 158 [Formula: see text] 3 ps FWHM 的 CTR。这种微弱的切伦科夫信号也存在于标准的 LSO 闪烁体中，与低 SPTR 值（<90 ps FWHM）一起，将与 FBK NUV-HD [Formula: see text] mm 耦合的[Formula: see text]mm LSO：Ce：Ca 的 CTR 提高到 61 [Formula: see text] 2 ps FWHM，使用 HF 电子，而当使用 NINO 前端 ASIC 进行读出时，其 CTR 为 73 [Formula: see text] 2 ps。当将 LSO：Ce：Ca 晶体与 FBK NUV-HD SiPM 耦合时，SiPM 的面积为[Formula: see text]mm，SPAD 尺寸为 40 [Formula: see text]m，使用 HF 电子，甚至可以实现[Formula: see text]mm 的 CTR 为 58 [Formula: see text] 3 ps，[Formula: see text]mm 的 CTR 为 98 [Formula: see text] 3 ps。此新的实验数据将允许进一步讨论基于闪烁体的探测器中的定时限制。
