Measurement of intrinsic rise times for various L(Y) SO and LuAG scintillators with a general study of prompt photons to achieve 10 ps in TOF-PET
Measurement of intrinsic rise times for various L(Y) SO and LuAG scintillators with a general study of prompt photons to achieve 10 ps in TOF-PET
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DOI：
10.1088/0031-9155/61/7/2802
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发表时间：
2016-04-07
影响因子：
3.5
通讯作者：
Lecoq, Paul
中科院分区：
文献类型：
--
作者：
Gundacker, Stefan;Auffray, Etiennette;Lecoq, Paul
公知的是，通常用于正电子发射断层摄影术中的基于闪烁体的探测器的符合时间分辨率（CTR）取决于闪烁衰减时间（τ（d））和探测到的光子数（n '），即CTR α根τ d/n'。然而，在闪烁过程开始时，闪烁上升时间（τ（d））和其他快速或瞬发光子（例如切伦科夫光子）在多大程度上影响CTR仍然是一个悬而未决的问题。本文测量了LSO：Ce、LYSO：Ce、LSO：Ce共掺Ca和LGSO：Ce晶体的闪烁发射率。对于测量的各种LSO型样品，我们发现闪烁上升时间的平均值为70 ps，尽管一些晶体如LSO：Ce共掺杂Ca似乎具有更快的上升时间，大约为20 ps。LuAG：Ce和LuAG：Pr的额外测量分别显示535 ps和251 ps的上升时间。对于这些晶体，可以在闪烁事件开始时观察到瞬发光子（切伦科夫）。此外，当与钙共掺杂时，观察到显著更低的上升时间值。为了定量研究上升时间对时间分辨率的影响，我们用相同的L（Y）SO样品测量了CTR，并将其值与Monte Carlo模拟进行了比较。使用测得的相对光产额，上升和衰减时间的反射器，我们能够定量地了解我们的模拟中测得的CTR。尽管上升时间对于充分解释测试的不同样品的CTR变化很重要，但我们确定其对CTR的影响仅为百分之几。这个结果是令人惊讶的，因为如果只考虑闪烁过程的光子统计学，CTR将与上升时间的平方根成比例。对CTR的意外的小的上升时间的影响，可以解释的卷积的闪烁率与单光子时间分辨率（SPTR）的光电探测器和晶体中的光子传播扩展（PTS）。进一步研究了闪烁过程开始时瞬发光子（Cherenkov等）的时序优势，得出了必须同时降低闪烁上升时间、SPTR和PTS才能充分利用这些快光子，从而显著提高CTR的结论。
The coincidence time resolution (CTR) of scintillator based detectors commonly used in positron emission tomography is well known to be dependent on the scintillation decay time (tau(d)) and the number of photons detected (n'), i.e. CTR alpha root tau d/n'. However, it is still an open question to what extent the scintillation rise time (tau(d)) and other fast or prompt photons, e.g. Cherenkov photons, at the beginning of the scintillation process influence the CTR. This paper presents measurements of the scintillation emission rate for different LSO type crystals, i.e. LSO:Ce, LYSO:Ce, LSO:Ce codoped Ca and LGSO:Ce. For the various LSO-type samples measured we find an average value of 70 ps for the scintillation rise time, although some crystals like LSO:Ce codoped Ca seem to have a much faster rise time in the order of 20 ps. Additional measurements for LuAG:Ce and LuAG:Pr show a rise time of 535 ps and 251 ps, respectively. For these crystals, prompt photons (Cherenkov) can be observed at the beginning of the scintillation event. Furthermore a significantly lower rise time value is observed when codoping with calcium. To quantitatively investigate the influence of the rise time to the time resolution we measured the CTR with the same L(Y)SO samples and compared the values to Monte Carlo simulations. Using the measured relative light yields, rise- and decay times of the scintillators we are able to quantitatively understand the measured CTRs in our simulations. Although the rise time is important to fully explain the CTR variation for the different samples tested we determined its influence on the CTR to be in the order of a few percent only. This result is surprising because, if only photonstatistics of the scintillation process is considered, the CTR would be proportional to the square root of the rise time. The unexpected small rise time influence on the CTR can he explained by the convolution of the scintillation rate with the single photon time resolution (SPTR) of the photodetector and the photon travel spread (PTS) in the crystal. The timing benefits of prompt photons at the beginning of the scintillation process (Cherenkov etc) are further studied, which leads to the conclusion that the scintillation rise time, SPTR and PTS have to he lowered simultaneously to fully profit from these fast photons in order to improve the CTR significantly.