Lu-Free Scintillators for PET

描述（由申请人提供）：正电子发射断层扫描（PET）是一种功能成像技术，具有量化体内生物过程速率的潜力。PET成像可以为癌症、阿尔茨海默病、头部创伤和中风等疾病的症状提供诊断。然而，为了充分利用PET的潜力，迫切需要提高PET系统的性能并降低其成本。这两个因素都受到现有探测器技术的强烈影响。闪烁晶体目前被用作PET的探测器。对用于PET的闪烁晶体的要求包括快速响应、高灵敏度、高光输出、高能量和时间分辨率以及低成本。目前，大多数PET系统使用Lu2SiO5:Ce （LSO）或其衍生物LYSO晶体，满足上述大部分要求。然而，在未来生产用于PET的闪烁体和开发潜在的新型闪烁体时，必须考虑到镥的成本和可用性问题。有几个不同的因素影响成本和可用性的氧化镥材料用于LSO/LYSO晶体生长PET，但也许最根本的是地质。镥的主要矿物来源是xenotime （LuPO4）和离子吸附粘土，这两种矿物主要分布在中国。其他国家很少生产镥。很难对中国在稀土出口方面的战略做出长期预测，但近年来，中国对稀土材料的生产控制和出口关税总体上有所提高。另一方面，钆也是一种对闪烁体有吸引力的稀土元素，可以在几种不同的矿物中找到，包括独居石，它存在于世界各地，从而使它的可用性较少依赖于一个国家的经济和政治。与镥相比，钆有一些额外的优点。它在地壳中的天然丰度比镥大一个数量级，而且它的离子尺寸更大，相对于较小的稀土离子（如镥），它更容易分离和纯化。这两个基本因素结合在一起，为相同纯度水平提供了显著降低成本的潜力（约为15倍）。较大的离子尺寸也意味着它为铈提供了一个取代位点，与相对较大的铈离子尺寸更好地匹配。最后，与镥不同的是，钆没有天然的放射性，这是一个额外的好处。考虑到人们对Lu的可用性和成本的严重担忧，该项目的目标是研究用于PET成像的新型无Lu闪烁体。其理念是实现降低成本，保持可预测的原材料供应，并超越LSO的性能。鉴于上述优点，我们计划设计基于Gd3+作为稀土离子的新型闪烁体，并将其纳入立方石榴石基体中。

DESCRIPTION (provided by applicant): Positron Emission Tomography (PET) is a functional imaging technique with the potential to quantify the rates of biological processes in vivo. PET imaging can provide diagnosis for symptoms of diseases such as cancer, Alzheimer's disease, head trauma, and stroke. However, to allow exploitation of the full potential of PET, there is urgent need for both improvement in the performance of PET systems and reduction in their cost. Both of these factors are strongly influenced by the available detector technology. Scintillation crystals are currently used as detectors in PET. Requirements for the scintillation crystals used in PET include fast response, high sensitivity, high light output, high energy and timing resolution, and low cost. At present, most PET systems use crystals of Lu2SiO5:Ce (LSO) or its derivative LYSO, which satisfy most of the requirements listed above. Nevertheless, issues remain with the cost and availability of lutetium that must be considered with respect to the future production of scintillators for PET and when developing potential new scintillators. There are several diverse factors that influence the cost and availability of the lutetium oxide material used in LSO/LYSO crystal growth for PET, but perhaps the most fundamental is geological. The main mineral sources for lutetium are xenotime (LuPO4) and ion adsorption clays, both of which are predominately found in China. There is very little production of lutetium from any other country. It is difficult to make long term predictions of China's strategy with respect to rare earth exports, but recent years have seen ever increasing production controls and higher tariffs on exported rare earth materials in general. On the other hand, gadolinium, also an attractive rare earth element for scintillators, can be found in several different minerals including monazite, which exist in various parts of the world, thus making it's availability less dependent on the economy and politics of a single nation. Gadolinium offers some additional advantages compared to lutetium. Its natural abundance in the earth's crust is an order of magnitude greater than lutetium, and its larger ionic size makes it considerably easier to separate and purify relative to the smaller rare earth ions such as lutetium. These two fundamental factors combine to offer the potential of significantly lower cost for the same level of purity (by a factor of ~15). The larger ionic size also means that it provides a substitutional site for cerium that is better matched to the relatively large size of the cerium ion. Finally, unlke lutetium, gadolinium has no natural radioactivity, an additional benefit. In view of the serious concerns about availability and cost of Lu, the goal of the proposed project is to investigate novel Lu-free scintillators for PET imaging. The idea is to achieve reduction in cost, maintain a predictable supply of raw materials, and exceed the performance of LSO. In view of the advantages cited above, we plan to design the new scintillator based on Gd3+ as the rare earth ion and incorporating it into a cubic garnet matrix.