Isotopes for New Modalities of PET/SPECT Imaging: Experimentation and Evaluation

常规的正电子发射计算机断层扫描和SPECT医学成像依赖于反投影技术，存在因伽马射线的散射和吸收而产生伪影的缺点，容易造成假阴性和/或假阳性诊断。分离同位素的双能量成像已被认为是改善图像质量的可能手段。它们总是涉及额外的设备、更高的剂量和更长的曝光时间等。我们尝试了一种新的方法，将PET/SPECT成像与单同位素相结合，在不到几纳秒的时间滞后内发射正电子和伽马射线。实施后，我们可以使用核物理和粒子物理实验的标准3D顶点重建技术。除了增强对比度外，该方法还提供基于不同软件切割的多幅图像和传统的反投影，以对图像伪影进行批判性评估，并将误诊降至最低。在确定候选同位素时，我们重点关注了同位素对人体的生物相容性、衰减校正的双重能量需求、经济可行性和生产的简便性、材料的稳定性等。候选同位素有43-Sc、73-Se、123-Xe、85-Y、77-Kr和75-Br，这些元素已经在医学上使用和摄取。*我是一个国际合作的首席调查员，成员来自加拿大、日本、韩国、印度和越南。我们将在UBC校区的日本大阪大学TRIUMF实验室和萨斯喀彻温大学的回旋加速器实验室进行质子和阿尔法束流实验，以确定最佳的束流能量和辐照时间，以最大限度地产生所选择的同位素，同时将干扰活动保持在最低限度。这项研究的下一阶段是放射化学分离程序，以开发临床上可用的同位素生产和分离方法，并将这一知识传递给卫生组织的最终用户。*一些同位素将在足够低的能量下制造，以便几个MeV高强度质子束的小回旋加速器，这将避免巨大的房地产或长途运输。这种PET/SPECT联合成像方式可以在现有的PET*机器上进行改造，只需对成像的硬件/软件稍作改动。我们将在实验室环境中使用原型探测器组件进行成像测试。*该项目完成后，将巩固加拿大在核医学成像研究和开发方面的领先地位。加拿大社会将受益，因为患者将获得更好的成像，更少的辐射剂量和更少的模糊性。放射科医生将拥有多个人体器官的图像，所有这些图像都是在一个环境中使用单一同位素获得的，能够对它们进行批判性评估，并对患者的病情做出更好的评估。******

The conventional medical imaging by PET and SPECT relies on back projection techniques and it has drawbacks of artifacts due to scattering and absorption of gamma rays, contributing to false negative and/or false positive diagnostics. Dual energy imaging with separate isotopes has been suggested as possible means of improving the image qualities. They invariably involve additional equipment, higher doses and longer exposures etc. We attempt a novel approach of combining PET/SPECT imaging with single isotopes which emit positrons and gamma rays within less than a few nano second time lags. When implemented, we can employ standard 3D- vertex reconstruction technique of nuclear and particle physics experiments. In addition to enhanced contrast, this method provides multiple images based on different software cuts with conventional back projection to evaluate the image artifacts critically and minimize false diagnostics. In identifying candidate isotopes, we focussed on biological compatibility of isotopes to humans, dual energy requirement for attenuation corrections, economic viability and ease of production, stability of materials etc. The candidate isotopes are 43-Sc, 73-Se, 123-Xe, 85-Y, 77-Kr and 75-Br, the elements of which are already in medical use and ingestion. ***I am the principal investigator of an international collaboration with members from Canada, Japan, Korea, India and Vietnam. We will perform experiments at Osaka university-Japan, TRIUMF- laboratory on UBC campus and at the cyclotron laboratory of the University of Saskatchewan with proton and alpha beams to determine the optimum beam energies and irradiation times to maximize the production of isotope of choice, while keeping the interfering activities to a minimum. The next phase of this research is radiochemical separation procedures to develop clinically usable isotope production and separation methods and pass on this knowledge to the end users in health organizations. ***Some of the isotopes are to be made at sufficiently low energies such that small cyclotrons of several MeV proton beams of high intensities, which will avoid huge real estate or long distance transportations. The modality of combined PET/SPECT can be retrofitted to existing PET***machines with minor changes of hardware/software of imaging. We will perform imaging tests with a prototype detector assembly in laboratory setting. ***This project, when completed, will consolidate the position of Canada as a leader of nuclear medial imaging research and development. Canadian society will benefit as the patients will get improved imaging with less radiation doses and less ambiguities. Radiologists will have multiple images of human organs, all obtained in one setting with a single isotope and be able to critically evaluate them and make better assessment of a patient condition. ******