Time-of-flight positron emission tomography using Cerenkov luminescence in bismuth germanate

摘要 正电子发射断层扫描(PET)作为一种诊断分子成像技术得到了广泛的应用 对人类医疗保健产生了重大影响。聚酯技术有了显著的改进 通过使用飞行时间(TOF)功能来测量两个511keV的到达时间的差异 伽马湮没射线。这种飞行时间信息在空间上限制了事件的起源，导致了改进 由于提高了PET扫描的信噪比(SNR)和有效灵敏度，因此可以获得更高的图像质量。 然而，闪烁体锗酸铋(BGO)在PET应用中具有几个比 L(Y)因此，如较高的阻止能力和较高的光电比例。BGO也没有后台活动 并且能够以比L(Y)更低的成本生产。然而，BGO的一个主要缺点是重合度不高 时间分辨率源于闪烁光子产生的中等光产额和较慢的衰减时间。 因此，BGO还没有被考虑用于当前一代的TOF PET扫描仪。 理论上，当511keV伽马射线在闪烁体中相互作用时，少量光学切伦科夫光子 由光电或康普顿相互作用释放的高能电子迅速产生。切伦科夫 光子是在极短的时间范围内产生的，而且比闪烁光子更早产生，因此 切伦科夫光子应该能为PET提供更好的时间信息。有趣的是，BGO拥有领先的属性 产生比其他闪烁体更多的切伦科夫光子。 最近，我们首次展示了瞬发切伦科夫光子对时间性质的影响 BGO使用我们的合作伙伴FBK开发的最新一代硅光电倍增管(SiPM)。因此，我们提出的 BGO的概念是使用切伦科夫光子来获得即时定时信息，而闪烁光子 为PET提供必要的能量信息。这项提议的主要目标是：1)改善重合度 探测更多切伦科夫光子用于TOF PET的BGO的时间分辨率，II)产生信号 切伦科夫光子和闪烁光子两者产生的信号的还原方法和读出电子学， 以及iii)最终开发和评估第一个实用的基于BGO的TOF PET探测器模块，它有5个 ×5cm2的横截面面积和符合时序分辨率为≤300ps半高宽。如果成功，这项提案 为开发灵敏度更高、成本更低的新型BGO基TOF PET扫描仪奠定了基础 目前的PET扫描仪。

SUMMARY Positron emission tomography (PET) is widely used as a diagnostic molecular imaging technique and clearly has had a significant impact on human healthcare. There have been significant improvements in PET technology by employing time-of-flight (TOF) capability that measures the difference in arrival time of the two 511 keV gamma annihilation rays. This TOF information spatially constrains the origin of the event, leading to improved image quality due to the increased signal-to-noise ratio (SNR) and effective sensitivity in the PET scan. The scintillator bismuth germanate (BGO), however, has several better properties for PET applications than L(Y)SO, such as higher stopping power and higher photo-electric fraction. BGO also has no background activity and can be produced at lower cost than L(Y)SO. However, a major drawback of BGO is the poor coincidence timing resolution originating from the moderate light yield and slow decay time of scintillation photon production. Therefore, BGO has not been considered for use in current generation TOF PET scanners. Theoretically, when a 511keV gamma ray interacts in a scintillator, a small number of optical Cerenkov photons are produced promptly by energetic electrons released by photoelectric or Compton interactions. The Cerenkov photons are produced within an extremely short time frame and earlier than scintillation photons, Thus the Cerenkov photons should provide better timing information for PET. Interestingly, BGO has properties that lead to it producing more Cerenkov photons than other scintillators. Recently, we showed, for the first time, the influence of prompt Cerenkov photons on the timing properties of BGO using latest generation silicon photomultipliers (SiPMs) developed by our partner FBK. Thus, our proposed concept for BGO is that Cerenkov photons are used to obtain prompt timing information while scintillation photons provide essential energy information for PET. The major goals of this proposal are i) to improve coincidence timing resolution of BGO by detecting more Cerenkov photons for TOF PET applications, ii) to develop signal reducing methods and read-out electronics for signals generated by both Cerenkov and scintillation photons, and iii) to finally develop and evaluate the first practical BGO-based TOF PET detector modules, which have 5 × 5 cm2 cross-sectional area and a coincidence timing resolution of ≤300 ps FWHM. If successful, this proposal forms the basis for developing novel BGO-based TOF PET scanners with higher sensitivity and lower cost than current PET scanners.