Lu-Free Scintillators for PET

描述(申请人提供)：正电子发射断层扫描(PET)是一种功能成像技术，有可能量化体内生物过程的速率。宠物成像可以为癌症、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，为了充分发挥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正电子发射体层析的探测器。用于PET的闪烁晶体要求响应速度快、灵敏度高、光输出高、能量分辨率高、时间分辨率高、成本低。目前，大多数聚酯系统使用的是Lu2SiO5：Ce(LSO)晶体或其衍生物lyso，满足了上面列出的大部分要求。然而，在今后生产PET用闪烁体和开发潜在的新闪烁体时，必须考虑到钚的成本和可获得性问题。影响用于LSO/LYSO晶体生长的材料的成本和可获得性的因素有多种，但最根本的可能是地质因素。钚的主要矿物来源是磷灰石(LuPO4)和离子吸附粘土，这两种矿物主要分布在中国矿床中。其他任何国家的钚产量都很少。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，中国不断加强生产控制，对出口稀土材料征收更高的关税。另一方面，Gd也是一种有吸引力的闪烁体稀土元素，可以在几种不同的矿物中找到，包括独居石，这些矿物存在于世界各地，因此它的可获得性不那么依赖于单一国家的经济和政治。相比于钚，Gd有一些额外的优点。它在地壳中的天然丰度比钚大一个数量级，而且它更大的离子尺寸使其相对于较小的稀土离子(如钚)更容易分离和提纯。这两个基本因素结合在一起，为相同水平的纯度提供了显著降低成本的潜力(降低了约15倍)。更大的离子尺寸也意味着它为Ce提供了一个替代位置，与相对较大的Ce离子更好地匹配。最后，除了钚，Gd没有天然的放射性，这是一个额外的好处。鉴于人们对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。这个想法是为了实现成本的降低，保持可预测的原材料供应，并超过LSO的表现。鉴于上述优点，我们计划设计一种新型的以Gd3为稀土离子的闪烁体，并将其融入到立方石榴石基质中。

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.