Thick scintillation detector with continuous positioning & DOI capability for PET

描述（由申请人提供）：这项工作的长期目标是开发一种通用、实用的PET探测器，该探测器可以在手头的成像情况下实现非常好的空间分辨率，而不会在其他重要特性（特别是灵敏度、能量和定时分辨率）方面产生重大影响。该项目的主要目标是设计一个厚（25毫米），连续探测器，具有独立的相互作用深度（DOI）测量。除了减少扫描仪中的视差效应之外，DOI测量还将使得能够对沿着深度（z）传播的3D光进行粗略采样，并在两个横向方向（x，y）上进行精细采样。通过对3D光扩散的这种表征，我们期望在厚探测器中保持良好的空间分辨率。与像素化检测器相比，易于制造和降低的成本、改进的填充分数以及良好或更好的能量和定时分辨率的承诺使得该检测器设计实用且高性能。与之前研究的连续探测器相比，其主要创新之处在于能够在大部分探测器FOV上实现并保持厚探测器的高空间分辨率，从而使探测器因其高灵敏度而成为PET成像的实用解决方案。该检测器的高空间分辨率与DOI测量一起将允许制造更小的环直径扫描器，这提供了增加的灵敏度、由于使用更少的闪烁体而降低的成本以及减少的湮灭光子非共线对空间分辨率的影响。最近的工作与薄晶体表明，它是有可能实现非常高的空间分辨率在连续探测器。然而，由于连续探测器中的光扩散是所有三个晶体尺寸的函数，并且导致定位算法的准确度退化，因此几乎不可能在探测器的整个视场（FOV）上保持这种空间分辨率，所述探测器足够厚以提供PET所需的高灵敏度。在这项工作中，我们将建立一个光导和独立的DOI测量解耦的3D性质的光传播在厚探测器，从而提高横向分辨率的使用。这项工作将导致探测器分裂成几个相互作用的深度水平，在每个级别内具有良好的横向分辨率。此外，我们将通过蒙特卡罗方法研究在这些探测器中匹配测量光扩散的能力。该蒙特卡罗将用于描述探测器中的全3D光扩散，这可以进一步提高空间分辨率，并且还可以简化探测器的校准过程。最后，不同的晶体材料和表面光洁度，以及不同的光采样技术，将通过模拟和测量进行研究，以实现良好的空间分辨率，同时保持这些探测器的能量和定时分辨率。在临床上，对于人体成像，当前一代PET扫描仪的有限空间分辨率导致小病变的测量摄取中的部分体积效应。通过将空间分辨率提高到最佳可能极限，临床诊断的总体疗效将显著提高，并且通常代表癌症初始阶段的小病变将足够早地被表征以指导治疗。因此，厚的连续探测器有可能显著影响临床成像情况和最终的患者治疗。

DESCRIPTION (provided by applicant): The long-term objective of this work is the development of a general, practical, PET detector that can achieve very good spatial resolution for the imaging situation at hand without a significant compromise in other important properties, specifically, sensitivity, and energy and timing resolutions. The primary goal of this project is to design a thick (25-mm), continuous detector with an independent depth-of-interaction (DOI) measurement. The DOI measurement, besides reducing parallax effect in the scanner, will enable a coarse sampling of the 3D light spread along the depth (z) and a fine sampling in the two transverse directions (x,y). With such a characterization of the 3D light spread, we expect to maintain good spatial resolution in the thick detector. The ease of manufacture and reduced cost, improved packing fraction, and promise of good or better energy and timing resolution compared to pixelated detectors, makes this detector design practical and high performance. The main innovation over previously investigated continuous detectors is the ability to achieve and maintain high spatial resolution in thick detectors over most of the detector FOV, making the detector a practical solution for PET imaging due to its high sensitivity. The high spatial resolution of this detector together with DOI measurement will allow the manufacture of smaller ring diameter scanners which provides increased sensitivity, reduced cost due to less scintillator used, and reduced annihilation photon non-collinearity effect on spatial resolution. Recent work with thin crystals suggests that it is possible to achieve very high spatial resolution in continuous detectors. However, since the light spread in a continuous detector is a function of all three crystal dimensions and leads to degeneracies in the accuracy of the positioning algorithm, it is almost impossible to maintain this spatial resolution over the entire field-of-view (FOV) of detectors that are thick enough to provide the high sensitivity needed for PET. In this work we will establish the use of a lightguide and independent DOI measurement to de-couple the 3D nature of the light spread in a thick detector, thus improving transverse resolution. This work will result in a splitting of the detector into several interaction depth levels, with good transverse resolution within each level. Also, we will investigate through Monte Carlo the ability to match the measured light spread in these detectors. This Monte Carlo will be used to describe the full 3D light spread in the detector that can further improve spatial resolution, and also lead to an easier calibration procedure for the detector. Finally, different crystal materials and surface finishes, as well as varying light sampling techniques, will be investigated through simulations and measurements to achieve good spatial resolution while maintaining the energy and timing resolution in these detectors. Clinically for human imaging, limited spatial resolution of current generation of PET scanners leads to partial volume effects in the measured uptake of small lesions. By improving the spatial resolution to the best possible limit, the overall efficacy of clinical diagnosis will be significantly improved and small lesions that often represent the initial stage of cancer will be characterized early enough to guide the therapy. Hence, thick continuous detectors have the potential to significantly impact the clinical imaging situation and the resultant patient treatment.