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，它可以在不显著影响其他重要特性的情况下实现非常好的空间分辨率，特别是灵敏度、能量和定时分辨率。该项目的主要目标是设计一种厚(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，还将实现沿深度(Z)传播的3D光的粗略采样和沿两个横向方向(x，y)的精细采样。有了这样的3D光扩散的表征，我们希望在厚探测器中保持良好的空间分辨率。与像素化探测器相比，这种探测器易于制造、降低成本、提高堆积率、具有良好或更好的能量和定时分辨率的前景，使该探测器设计实用和高性能。与以前研究的连续探测器相比，主要的创新是能够在大部分探测器视野上实现并保持厚探测器的高空间分辨率，使探测器因其高灵敏度而成为PET成像的实用解决方案。这种探测器的高空间分辨率与DOI测量相结合，将允许制造更小的环直径扫描仪，从而提供更高的灵敏度，由于使用更少的闪烁体而降低成本，并减少湮灭光子非共线性对空间分辨率的影响。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，并导致定位算法的精度退化，因此几乎不可能在厚度足以提供PET所需的高灵敏度的探测器的整个视场(FOV)上保持这种空间分辨率。在这项工作中，我们将使用光导和独立的DOI测量来分离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级别，在每个级别内具有良好的横向分辨率。此外，我们还将通过蒙特卡洛研究与这些探测器中测量的光传播相匹配的能力。这种蒙特卡罗方法将被用来描述探测器中的全部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变得更容易。最后，将通过模拟和测量来研究不同的晶体材料和表面光洁度，以及不同的光采样技术，以在保持这些探测器的能量和时间分辨率的同时获得良好的空间分辨率。临床上，对于人体成像来说，当前一代PET扫描仪的空间分辨率有限导致在测量的小病变摄取中存在部分体积效应。通过将空间分辨率提高到可能的最佳限度，临床诊断的整体效果将显著提高，通常代表癌症初期的小病变将足够早地被特征化，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.