Helical Pinhole SPECT for Small-Scale Quantification

描述(由申请人提供)： 该项目的总体目标是开发一种SPECT系统，该系统利用跟随螺旋轨道的针孔准直器来量化小动物中的放射性示踪剂分布。SPECT成像是一种廉价的技术，可以在人类疾病的小动物模型中对各种化合物进行体内定量。该系统将结合针孔准直器用于研究微小物体的优良特性，在小旋转半径(ROR)时显著提高放大倍数和灵敏度，以及螺旋轨道的采样特性。圆形针孔轨道不能完全采样感兴趣的对象，导致在后续重建中采样伪影；随着RoR的降低，伪影恶化，导致采样与灵敏度和放大之间的权衡。另一方面，针孔准直器的螺旋轨道允许以较小的ROR进行完全采样，从而可以从在高灵敏度和高放大倍率下获得的投影数据进行无伪影重建。可行性阶段(R21)的主要目标是演示从螺旋针孔投影数据进行无伪影重建。在可行性阶段之后，将进一步开发该系统，以提供定量的放射性示踪剂分布。定量SPECT将需要衰减和散射补偿。透射源将被添加到系统以确定对象的衰减图，这是衰减补偿的必要组件。一些散射补偿算法也使用衰减贴图。衰减图将促进衰减和散射补偿软件和技术的开发，而不会在集成X射线计算机层析成像(XCT)系统的初始阶段增加复杂性。此外，还将研究螺旋轨道参数以及孔径参数，以确定它们与重建质量的关系。实验模型将是评估该系统量化放射性示踪剂分布能力的主要工具。软件模拟和数值计算将补充实验结果。从长远来看，希望将螺旋针孔SPECT系统升级为XCT系统，以取代传输源。当XCT系统与SPECT系统相结合时，将提供内在联合配准的SPECT/XCT图像，将功能信息与解剖信息融合在一起。该系统的另一个长期愿景是将其微型化为桌面研究仪器。

DESCRIPTION (provided by applicant): The overall goal of this project is to develop a SPECT system that utilizes pinhole collimators following helical orbits for quantifying radiotracer distributions in small animals. SPECT imaging is an inexpensive technique for in vivo quantification of various compounds in small-animal models of human disease. The system will combine the excellent properties of pinhole collimators for studying small objects, dramatically increasing magnification and sensitivity at small radius of rotation (ROR), with the sampling properties of helical orbits. Circular pinhole orbits do not completely sample the object of interest leading to sampling artifacts in the subsequent reconstructions; the artifacts worsen as the ROR decreases, causing a trade-off between sampling and both sensitivity and magnification. On the other hand, helical orbits of pinhole collimators allow complete sampling with a small ROR resulting in artifact-free reconstructions from projection data acquired at high sensitivity and magnification. The primary goal of the feasibility (R21) phase is the demonstration of artifact-free reconstructions from helical pinhole projection data. Following the feasibility phase, the system will be further developed to provide quantitative radiotracer distributions. Quantitative SPECT will require both attenuation and scatter compensation. A transmission source will be added to the system to determine the object's attenuation map, a necessary component for attenuation compensation. Some scatter compensation algorithms also utilize attenuation maps. The attenuation map will facilitate the development of software and techniques for attenuation and scatter compensation without the added complexity in the initial phase of integrating an x-ray computed tomography (XCT) system. In addition, the parameters of the helical orbit, in conjunction with the aperture parameters, will be investigated to determine their relationship to the quality of reconstructions. Experimental phantoms will be the primary tool used to evaluate the system's ability to quantify the radiotracer distribution. Software simulations and numerical calculations will complement experimental results. In the longer term, it is desirable to upgrade the spiral pinhole SPECT system with an XCT system to replace the transmission source. The XCT system, when combined with the SPECT system, will provide inherently co-registered SPECT/XCT images that will fuse functional information with anatomical information. Another long-term vision for this system is its miniaturization to a table-top research instrument.