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成像可以提供疾病症状的诊断，如癌症、阿尔茨海默病、头部创伤和中风。然而，为了允许开发PET的全部潜力，迫切需要改善PET系统的性能并降低其成本。这两个因素都受到现有检测器技术的强烈影响。闪烁晶体目前用作PET中的探测器。对PET中使用的闪烁晶体的要求包括快速响应、高灵敏度、高光输出、高能量和定时分辨率以及低成本。目前，大多数PET系统使用Lu 2SiO 5：Ce（LSO）或其衍生物LYSO的晶体，其满足上面列出的大多数要求。然而，在未来生产PET用澄清剂和开发潜在的新澄清剂时必须考虑的镥的成本和可用性问题仍然存在。有几个不同的因素影响用于PET的LSO/LYSO晶体生长的氧化镥材料的成本和可用性，但也许最根本的是地质。镥的主要矿物来源是磷钇矿（LuPO 4）和离子吸附粘土，这两种矿物主要在中国发现。其他国家的镥产量很少。很难对中国的稀土出口战略做出长期预测，但近年来，中国对出口稀土材料的生产控制不断加强，关税普遍提高。另一方面，钆，也是一种有吸引力的稀土元素，可以在世界各地存在的几种不同的矿物中找到，包括独居石，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，钆提供了一些额外的优点。它在地壳中的天然丰度比镥大一个数量级，其较大的离子尺寸使其相对于较小的稀土离子（如镥）更容易分离和纯化。这两个基本因素联合收割机提供了在相同纯度水平下显著降低成本的潜力（约15倍）。较大的离子尺寸也意味着它为铈提供了与相对较大尺寸的铈离子更好匹配的取代位点。最后，除了镥，钆没有天然放射性，这是一个额外的好处。鉴于对Lu的可用性和成本的严重关注，所提出的项目的目标是研究用于PET成像的新型无Lu制冷剂。其理念是降低成本，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Gd 3+作为稀土离子并将其纳入立方石榴石基质的新闪烁体。

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.