TOF-PET with high-efficiency TlCl crystals

摘要 飞行时间正电子发射断层扫描是一种非常有效的核成像方式，用于诊断和诊断 一系列病理疾病的分期，如癌症、心血管疾病或肌肉骨骼疾病。 商用TOF-PET扫描仪目前使用的是正硅酸锶(L(Y)SO)晶体探测器 耦合到硅光电倍增管(SiPM)以实现200-500 ps之间的符合时间分辨率(CTR 半高全宽(FWHM)。 L(Y)SO晶体高昂的生产成本及其本征辐射背景目前阻碍了 非常有前景的TOF-PET模式的发展和推广，如长轴向视野(LA-FOV)扫描仪 或涉及极低剂量的研究，如细胞跟踪或使用电疗剂进行成像。新型闪烁体 需要生产成本较低、无辐射本底、具有TOF级定时精度的材料。 我们建议使用氯化铊(TlCl)作为TOF-PET的闪烁材料。TlCl是一种具有简单的 立方体结构，允许相对简单和灵活的掺杂过程。用TlCl获得的初步数据 掺铍(Be)和铟(I)的晶体显示出~10 ns的非常快的闪烁分量，具有 对于非常精确的定时测量具有很高的潜力。TlCl的检测效率比Lyso甚至更高 用于511keV伽马的锗酸铋(BGO)是无本底辐射的，其生产成本估算 是L(Y)SO的三分之一，因为它的低熔点为430C(而L(Y)SO的熔点为2050C)和简单晶格 结构。此外，与BGO不同，TlCl独一无二地结合了非常快的闪烁过程和高切伦科夫 发电收益率，以进一步提高计时潜力。 我们的目标是通过结合晶体生长方面的专业知识来证明使用TlCl探测器进行TOF-PET的可行性。 模拟光的产生和检测，以及台式机的特性。首先，将研究Be和Be的影响 I作为TlCl中的掺杂剂，目的是进一步改善在初步数据中观察到的闪烁性能。 我们还将优化TlCl的表面处理，以最大限度地提高对光电探测器的光提取。 其次，我们将开发一个模拟框架，使我们能够指导晶体开发过程并 了解TlCl的基本时间限制。第三，我们将用不同的方法来表征单个TlCl晶体 光电探测器的选择，以评估其计时和能量分辨率精度。使用这些工具获得的结果 晶体也将被用来调整和验证模拟模型。最后，我们将对性能进行评估 4x4晶体元素的TlCl探测器块。我们将评估它们的时间分辨率、交互深度 洪水直方图的估计精度和质量。

Summary Time-of-flight positron emission tomography is a very effective nuclear imaging modality for the diagnosis and staging of a range of pathologies such as cancer, cardiovascular diseases, or musculoskeletal disorders. Commercial TOF-PET scanners currently employ lutetium-(yttrium)-oxyorthosilicate (L(Y)SO) crystal detectors coupled to silicon photomultipliers (SiPMs) to achieve coincidence time resolutions (CTR) between 200-500 ps full width at half maximum (FWHM). High production costs of L(Y)SO crystals and their intrinsic radiation background are currently hindering the evolution and spread of very promising TOF-PET modalities such as long axial field-of-view (LA-FOV) scanners or studies involving very low doses such as cell tracking or imaging with theranostic agents. New scintillator materials with lower production cost, radiation background-free, and with TOF-level timing accuracy are needed. We propose to use thallium chloride (TlCl) as a scintillator material for TOF-PET. TlCl is a material with a simple cubic structure that allows for a relatively easy and flexible doping process. Preliminary data obtained with TlCl crystals doped with beryllium (Be) and indium (I) show a very fast scintillation component of ~10 ns that has a high potential for very accurate timing measurements. TlCl has a greater detection efficiency than LYSO or even bismuth germanate (BGO) for 511 keV gammas, is background radiation-free, and its estimated production cost is 1/3 of L(Y)SO based on its low melting point of 430C (compared to 2050C for L(Y)SO) and simple lattice structure. Moreover, unlike BGO, TlCl uniquely combines a very fast scintillation process with a high Cherenkov generation yield to further boost timing potential. We aim to prove the feasibility of using TlCl detectors for TOF-PET by combining expertise in crystal growth, simulation of light generation and detection, and benchtop characterization. First, will study the effects of Be and I as dopants in TlCl with the aim of further improve the scintillation properties observed in the preliminary data. We will also optimize the surface treatment of TlCl to maximize the light extraction toward the photodetector. Second, we will develop a simulation framework that allows us to guide the crystal development process and to understand the fundamental timing limits of TlCl. Third, we will characterize individual TlCl crystals with different choices of photodetectors to evaluate their timing and energy resolution accuracy. Results obtained with these crystals will be used to tune and validate the simulation model as well. Finally, we will evaluate the performance of TlCl detector blocks of 4x4 crystal elements. We will evaluate their timing resolution, depth-of-interaction estimation accuracy, and quality of flood histograms.