CIEMAT (Centro de Investigaciones Energéticas, Medioambientales y Tecnológicas), Madrid, Spain.
Phys Med Biol. 2011 Jan 7;56(1):273-88. doi: 10.1088/0031-9155/56/1/016. Epub 2010 Dec 9.
Monte Carlo-based modelling is a powerful tool to help in the design and optimization of positron emission tomography (PET) systems. The performance of these systems depends on several parameters, such as detector physical characteristics, shielding or electronics, whose effects can be studied on the basis of realistic simulated data. The aim of this paper is to validate a comprehensive study of the Raytest ClearPET small-animal PET scanner using a new Monte Carlo simulation platform which has been developed at CIEMAT (Madrid, Spain), called GAMOS (GEANT4-based Architecture for Medicine-Oriented Simulations). This toolkit, based on the GEANT4 code, was originally designed to cover multiple applications in the field of medical physics from radiotherapy to nuclear medicine, but has since been applied by some of its users in other fields of physics, such as neutron shielding, space physics, high energy physics, etc. Our simulation model includes the relevant characteristics of the ClearPET system, namely, the double layer of scintillator crystals in phoswich configuration, the rotating gantry, the presence of intrinsic radioactivity in the crystals or the storage of single events for an off-line coincidence sorting. Simulated results are contrasted with experimental acquisitions including studies of spatial resolution, sensitivity, scatter fraction and count rates in accordance with the National Electrical Manufacturers Association (NEMA) NU 4-2008 protocol. Spatial resolution results showed a discrepancy between simulated and measured values equal to 8.4% (with a maximum FWHM difference over all measurement directions of 0.5 mm). Sensitivity results differ less than 1% for a 250-750 keV energy window. Simulated and measured count rates agree well within a wide range of activities, including under electronic saturation of the system (the measured peak of total coincidences, for the mouse-sized phantom, was 250.8 kcps reached at 0.95 MBq mL(-1) and the simulated peak was 247.1 kcps at 0.87 MBq mL(-1)). Agreement better than 3% was obtained in the scatter fraction comparison study. We also measured and simulated a mini-Derenzo phantom obtaining images with similar quality using iterative reconstruction methods. We concluded that the overall performance of the simulation showed good agreement with the measured results and validates the GAMOS package for PET applications. Furthermore, its ease of use and flexibility recommends it as an excellent tool to optimize design features or image reconstruction techniques.
基于蒙特卡罗的建模是一种强大的工具，可以帮助设计和优化正电子发射断层扫描（PET）系统。这些系统的性能取决于几个参数，例如探测器物理特性、屏蔽或电子学，这些参数的影响可以基于真实的模拟数据进行研究。本文的目的是验证在西班牙马德里的 CIEMAT 开发的新的蒙特卡罗模拟平台（称为 GAMOS（基于 GEANT4 的医学模拟架构））对 Raytest ClearPET 小动物 PET 扫描仪的全面研究。该工具包基于 GEANT4 代码，最初设计用于涵盖放射治疗到核医学领域的多个医学物理应用，但后来被其一些用户应用于物理的其他领域，例如中子屏蔽、空间物理、高能物理等。我们的模拟模型包括 ClearPET 系统的相关特征，即双相闪烁晶体层，旋转龙门架，晶体中的固有放射性或用于离线符合排序的单个事件存储。模拟结果与实验采集进行对比，包括根据国家电器制造商协会（NEMA）NU 4-2008 协议进行的空间分辨率、灵敏度、散射分数和计数率研究。空间分辨率结果表明，模拟值与测量值之间的差异等于 8.4%（在所有测量方向上最大 FWHM 差异为 0.5 毫米）。在 250-750keV 能量窗口内，灵敏度结果的差异小于 1%。在广泛的活动范围内，模拟和测量的计数率吻合良好，包括在系统电子饱和下（对于鼠大小的体模，总符合的测量峰值为 250.8k cps，达到 0.95MBq mL(-1)，模拟峰值为 247.1k cps，达到 0.87MBq mL(-1)）。在散射分数比较研究中，获得了优于 3%的一致性。我们还测量并模拟了一个微型 Derenzo 体模，使用迭代重建方法获得了相似质量的图像。我们得出结论，模拟的整体性能与测量结果吻合良好，验证了 GAMOS 包适用于 PET 应用。此外，其易用性和灵活性使其成为优化设计特征或图像重建技术的优秀工具。
