The system response of a gamma camera is dependent on the photon energy, thus the energy-dependent response function needs to be considered to improve the quality and fidelity of reconstructed images for identifying radionuclides in security applications. In this study, two reconstruction strategies using the maximum-likelihood expectation maximization (MLEM) algorithm with the multi-energy system matrices calculated by Monte Carlo simulations are proposed. The difference between the two is in data acquisition; one uses the sum of all events into a single projection image while the other sorts them into separate energy windows. Various radiation images of gamma-ray sources were simulated with a Monte Carlo code, and an actual image was acquired with a gamma camera. Both simulation and experiment results demonstrated the feasibility of the presented multi-energy reconstruction strategies in the detection of orphan sources.

伽马相机的系统响应取决于光子能量，因此需要考虑能量相关的响应函数，以提高用于安全应用中识别放射性核素的重建图像的质量和保真度。在这项研究中，提出了两种使用最大似然期望最大化（MLEM）算法和蒙特卡罗模拟计算的多能量系统矩阵的重构策略。两者之间的区别在于数据获取。一个将所有事件的总和合并为一个投影图像，而另一个将它们分类为单独的能量窗口。用蒙特卡罗代码模拟各种伽玛射线源的辐射图像，并用伽玛相​​机获取实际图像。