DEPTH OF INTERACTION MEASUREMENT IN ANGER CAMERAS

几家商业公司最近推出了能够同时进行符合光子和单光子成像的双头愤怒相机系统。这些系统有可能成为许多社区医院专用正电子发射断层扫描(PET)系统的替代品。然而，就系统灵敏度和空间分辨率而言，这些系统的符合成像性能目前明显低于专用的最先进的PET系统。为了提高符合成像的整体探测效率，在这些多用途系统中使用了厚的NaI(Tl)晶体。不幸的是，厚晶体会增加视差误差，当双角度相机系统在符合成像模式下操作时，视差误差会降低重建的图像分辨率；厚晶体也会降低固有的空间分辨率性能，特别是在成像低能量单光子示踪器时。如果测量探测到的伽马射线的相互作用深度(DOI)，则可以最大限度地减少视差误差的影响。此外，我们相信同样的DOI信息可以用来提高固有的空间分辨率。我们提出了一种利用波长移位(WLS)闪烁光纤与大面积NaI(Tl)晶体入射面耦合的方法来测量测距相机DOI的可行性。我们假设由闪烁光纤测量的光输出分布随着DOI的变化而变化：分布的宽度随着相互作用部位距离入射面的距离而变宽。在这项研究中，我们将开发使用WLS闪烁光纤进行DOI测量所需的硬件和软件，特别是用于商业多用途双头测角相机系统的厚的大面积NaI(Tl)晶体。我们将评估我们的方法减少符合成像中的视差误差的能力。我们还将研究在三维线性校正技术中利用得到的DOI信息来提高测角相机的平面本征空间分辨率的可能性。

Several commercial companies have recently introduced dual-head Anger camera systems capable of both coincidence-photon and single-photon imaging. These systems may have the potential to be an alternative to dedicated positron emission tomography (PET) systems for many community hospitals. However, the coincidence-imaging performance of these systems, in terms of system sensitivity and spatial resolution, currently falls significantly short of that of dedicated state-of-the-art PET systems. To increase the overall detection efficiency for coincidence imaging, thick NaI(Tl) crystals are being used in these multi-purpose systems. Unfortunately, thick crystals enhance parallax errors that degrade reconstructed image resolution when the dual-Anger camera system is operated in coincidence-imaging mode; thick crystals also degrade intrinsic spatial resolution performance, particularly when imaging low- energy single-photon tracers. The effects of parallax errors can be minimized if the depth of interaction (DOI) of detected gamma rays is measured. In addition we believe the same DOI information could be used to improve intrinsic spatial resolution. We propose to study the feasibility of a method to use wavelength-shifting (WLS) scintillating optical fibers, coupled in a linear array to the entrance face of a large-area NaI(Tl) crystal, to measure DOI in Anger cameras. We hypothesize that the light output distribution measured by the scintillation fibers varies with DOI: the width of the distribution broadens as the site of interaction moves farther from the entrance face. In this research, we will develop the hardware and software necessary for performing DOI measurement with WLS scintillating fibers, particularly for thick large- area NaI(Tl) crystals like those used in commercial multi-purpose dual- head Anger camera systems. We will evaluate the ability of our approach to reduce parallax errors in coincidence imaging. We also will investigate the potential use of the derived DOI information in 3-D linearity correction techniques to the improve planar intrinsic spatial resolution of Anger cameras.