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的、实用的PET探测器，它可以在不影响其他重要特性（特别是灵敏度、能量和时间分辨率）的情况下，为手头的成像情况实现非常好的空间分辨率。该项目的主要目标是设计一个厚（25毫米）的连续探测器，具有独立的相互作用深度（DOI）测量。DOI测量除了减少扫描仪中的视差效应外，还可以对沿深度(z)传播的3D光进行粗采样，并在两个横向（x,y）进行细采样。有了这样的三维光传播特性，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，易于制造和降低成本，提高封装比例，并承诺具有良好或更好的能量和时间分辨率，使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，主要的创新是能够在大多数探测器视场范围内实现并保持高空间分辨率，使探测器成为PET成像的实用解决方案，因为它的高灵敏度。该探测器的高空间分辨率以及DOI测量将允许制造更小的环形直径扫描仪，从而提供更高的灵敏度，由于使用较少的闪烁体而降低成本，并减少湮灭光子对空间分辨率的非共线性影响。最近对薄晶体的研究表明，在连续探测器中实现非常高的空间分辨率是可能的。然而，由于连续探测器中的光传播是所有三个晶体尺寸的函数，并导致定位算法精度的退化，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，因为探测器的厚度足以提供PET所需的高灵敏度。在这项工作中，我们将建立使用光波导和独立的DOI测量来解耦厚探测器中光传播的3D性质，从而提高横向分辨率。这项工作将导致探测器分裂成几个相互作用深度水平，在每个水平内具有良好的横向分辨率。此外，我们将通过蒙特卡罗研究在这些探测器中匹配测量光传播的能力。该蒙特卡罗将用于描述探测器中的全3D光传播，这可以进一步提高空间分辨率，并使探测器的校准过程更容易。最后，不同的晶体材料和表面处理，以及不同的光采样技术，将通过模拟和测量来研究，以获得良好的空间分辨率，同时保持这些探测器的能量和时间分辨率。临床上用于人体成像，当前一代PET扫描仪有限的空间分辨率导致小病变的测量摄取部分体积效应。通过将空间分辨率提高到最大限度，将显著提高临床诊断的整体效果，并尽早发现通常代表癌症初始阶段的小病变，从而指导治疗。因此，厚连续检测器有可能显著影响临床成像情况和由此产生的患者治疗。

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.