Improving accuracy in small-animal cardiac SPECT/CT imaging

使用单光子发射计算机断层扫描(MicroSPECT)进行小动物成像对于及时开发新的放射性示踪剂以及提高我们对心力衰竭等重要疾病的认识和治疗是至关重要的。它允许在体内三维评估示踪剂在同一动物体内的多个时间点的分布和器官功能。到目前为止，这一领域的工作取得了非常有希望的成果，但要充分发挥其潜力，还需要进一步的工作。显微成像面临着与临床成像不同的挑战和要求，这改变了系统物理各个方面的重点。由于受试者(小鼠和大鼠)的体积很小，所以对分辨率的重视程度很高，这导致了对针孔SPECT成像的转变。针孔准直器的使用导致了整个视场的分辨率、放大率和灵敏度的变化。此外，使用多个针孔来抵消低灵敏度可能导致投影中的信号重叠，从而在用于图像重建的数据中引入歧义。在小动物身上，光子衰减和散射的影响会减少，但不会消除，在这种更复杂的图像采集环境中，仍然需要补偿这些影响。最后，小动物SPECT相对于竞争技术的优势之一是它能够使用不同的同位素同时探测多种信号。然而，这些信号的分离并不完全，需要对剩余的干扰进行校正。虽然存在从临床成像到校正其中许多影响的各种方法，但需要对这些技术进行修改以优化它们以用于微成像，并且这些技术对微成像的准确性和精密度的影响目前尚不清楚。这项工作意义重大，因为显微成像所致力于的任务的基础科学性质要求高水平的定量精度。小动物SPECT的改进将增强我们快速开发和评估新的放射性示踪剂的能力，并研究疾病发生和发展过程中的基本过程，如细胞凋亡和血管生成。

Small animal imaging with single-photon emission computed tomography (microSPECT) is central to the timely development of new radiotracers and to improving our understanding and treatment of important diseases like heart failure. It allows for in vivo 3D assessment of tracer distribution and organ function over multiple time points in the same animal. Work in this field to date has yielded very promising results, but further work is required to realize its full potential. Micro-imaging faces different challenges and demands than clinical imaging and this alters the emphasis of various aspects of the physics of the system. There is a strong emphasis on resolution due to the very small size of the subjects (mice and rats) which has led to a shift to pinhole SPECT imaging. The use of pinhole collimators results in variable resolution, magnification, and sensitivity across the field of view. In addition, the use of multiple pinholes to offset poor sensitivity can lead to overlap of the signals in the projections and thus introduce ambiguity in the data used for image reconstruction. The effects of photon attenuation and scatter are reduced in small-animals but not eliminated, and there remains a need to compensate for these effects in this more complex image-acquisition environment. Finally, one of the strengths of small-animal SPECT over competing technology is its ability to use different isotopes to probe multiple signals simultaneously. Nevertheless, the separation of these signals is not complete and correction for the remaining interference is required. While various methods exist from clinical imaging to correct for many of these effects, modification of these techniques to optimize them for micro-imaging is needed and the impact of these on the accuracy and precision of micro-imaging is presently unknown. This work is significant because the basic science nature of the tasks to which micro-imaging is devoted demand a high level of quantitative accuracy. Improvements in small-animal SPECT will enhance our ability to rapidly develop and evaluate new radiotracers and to study fundamental processes such as apoptosis and angiogenesis during the onset and progression of disease.