Eriksson Ida, Starck Sven-Ake, Båth Magnus
Department of Medical Physics, Karlstad Hospital, SE-651 85 Karlstad, Sweden.
Radiat Prot Dosimetry. 2010 Apr-May;139(1-3):219-27. doi: 10.1093/rpd/ncq055. Epub 2010 Feb 19.
The purpose of the present work was to investigate the validity of using the Monte Carlo technique for determining the detective quantum efficiency (DQE) of a gamma camera system and to use this technique in investigating the DQE behaviour of a gamma camera system and its dependency on a number of relevant parameters. The Monte Carlo-based software SIMIND, simulating a complete gamma camera system, was used in the present study. The modulation transfer function (MTF) of the system was determined from simulated images of a point source of (99m)Tc, positioned at different depths in a water phantom. Simulations were performed using different collimators and energy windows. The MTF of the system was combined with the photon yield and the sensitivity, obtained from the simulations, to form the frequency-dependent DQE of the system. As figure-of-merit (FOM), the integral of the 2D DQE was used. The simulated DQE curves agreed well with published data. As expected, there was a strong dependency of the shape and magnitude of the DQE curve on the collimator, energy window and imaging position. The highest FOM was obtained for a lower energy threshold of 127 keV for objects close to the detector and 131 keV for objects deeper in the phantom, supporting an asymmetric window setting to reduce scatter. The Monte Carlo software SIMIND can be used to determine the DQE of a gamma camera system from a simulated point source alone. The optimal DQE results in the present study were obtained for parameter settings close to the clinically used settings.
本研究的目的是探讨使用蒙特卡罗技术确定γ相机系统的探测量子效率（DQE）的有效性，并利用该技术研究γ相机系统的DQE行为及其对一些相关参数的依赖性。本研究使用了基于蒙特卡罗的软件SIMIND，该软件可模拟完整的γ相机系统。系统的调制传递函数（MTF）由位于水模不同深度的（99m）Tc点源的模拟图像确定。使用不同的准直器和能量窗进行模拟。将系统的MTF与模拟得到的光子产额和灵敏度相结合，形成系统的频率相关DQE。作为品质因数（FOM），使用二维DQE的积分。模拟的DQE曲线与已发表的数据吻合良好。正如预期的那样，DQE曲线的形状和大小强烈依赖于准直器、能量窗和成像位置。对于靠近探测器的物体，较低能量阈值为127 keV，对于水模中较深的物体，较低能量阈值为131 keV时，可获得最高的FOM，这支持采用非对称窗设置以减少散射。蒙特卡罗软件SIMIND可单独用于从模拟点源确定γ相机系统的DQE。本研究中，在接近临床使用设置的参数设置下获得了最佳的DQE结果。
