CT scanner x-ray spectrum estimation from transmission measurements
CT scanner x-ray spectrum estimation from transmission measurements
复制标题
DOI：
10.1118/1.3547718
复制
发表时间：
2011-02-01
期刊：
影响因子：
3.8
通讯作者：
McCollough, Cynthia H.
中科院分区：
文献类型：
--
作者：
Duan, Xinhui;Wang, Jia;McCollough, Cynthia H.
目的：在诊断CT成像中，许多重要的应用依赖于对X射线能谱的了解，包括蒙特卡罗剂量计算和双能材料分解分析。由于所涉及的光子通量很高，很难直接从CT扫描仪的X射线管中测量光谱。间接测量的一种潜在方法涉及从传输测量中估计频谱。期望最大化(EM)方法是解决这一问题的一种准确而稳健的方法。本文在一台商用CT扫描仪上对该方法进行了评估。方法：使用聚碳酸酯和铝两种阶梯楔形材料来产生不同的衰减水平。在扫描仪上进行透射率测量，并将来自扫描仪的测量数据输出到外部计算机以计算光谱。用EM方法求解了表示多色X射线光子衰减过程的方程。将估计的光谱与使用扫描仪制造商提供的软件模拟的光谱进行比较。为了测试光谱的准确性，使用包含不同深度的水模进行了验证实验。结果：对双源CT扫描仪的80、100、120和140kVp的光谱进行了估算。估算的光谱与模拟的光谱吻合较好。平均能量差小于1keV。在验证实验中，透射值的实测值与计算值吻合良好。结论：利用透射率数据和EM方法进行谱估计是一种定量准确且稳健的CT系统谱估计技术。这种方法可以帮助研究依赖于CT扫描仪的X射线谱的准确知识。(C)2011年美国医学物理学家协会。[DOI：10.1118/1.3547718]
Purpose: In diagnostic CT imaging, multiple important applications depend on the knowledge of the x-ray spectrum, including Monte Carlo dose calculations and dual-energy material decomposition analysis. Due to the high photon flux involved, it is difficult to directly measure spectra from the x-ray tube of a CT scanner. One potential method for indirect measurement involves estimating the spectrum from transmission measurements. The expectation maximization (EM) method is an accurate and robust method to solve this problem. In this article, this method was evaluated in a commercial CT scanner.Methods: Two step-wedges (polycarbonate and aluminum) were used to produce different attenuation levels. Transmission measurements were performed on the scanner and the measured data from the scanner were exported to an external computer to calculate the spectra. The EM method was applied to solve the equations that represent the attenuation processes of polychromatic x-ray photons. Estimated spectra were compared to the spectra simulated using a software provided by the manufacturer of the scanner. To test the accuracy of the spectra, a verification experiment was performed using a phantom containing different depths of water. The measured transmission data were compared to the transmission values calculated using the estimated spectra.Results: Spectra of 80, 100, 120, and 140 kVp from a dual-source CT scanner were estimated. The estimated and simulated spectra were well matched. The differences of mean energies were less than 1 keV. In the verification experiment, the measured and calculated transmission values were in excellent agreement.Conclusions: Spectrum estimation using transmission data and the EM method is a quantitatively accurate and robust technique to estimate the spectrum of a CT system. This method could benefit studies relying on accurate knowledge of the x-ray spectra from CT scanner. (C) 2011 American Association of Physicists in Medicine. [DOI: 10.1118/1.3547718]