Generalizing the MTF and DQE to include x-ray scatter and focal spot unsharpness: Application to a new microangiographic system
Generalizing the MTF and DQE to include x-ray scatter and focal spot unsharpness: Application to a new microangiographic system
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DOI：
10.1118/1.1844151
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发表时间：
2005-02-01
期刊：
影响因子：
3.8
通讯作者：
Hoffmann, KR
中科院分区：
文献类型：
--
作者：
Kyprianou, LS;Rudin, S;Hoffmann, KR
当成像系统包括焦斑不清晰和患者散射时，使用调制传递函数（MTF）和探测量子效率（DQE）的探测器表征不能充分预测图像质量。MTF、噪声功率谱、噪声等效量子和DQE的概念被引用到物平面，并被推广到包括由于焦斑的有限尺寸引起的几何不清晰度的影响以及由于患者引起的X射线散射的空间分布和幅度的影响。广义量提供考虑完整成像系统的性能特性，但减少到没有放大或散射的检测器属性的描述。我们已经评估了一种新的神经血管造影成像系统的基础上的区域感兴趣（ROI）的微血管造影检测器使用这些广义量。使用均匀的头部等效体模作为过滤器和X射线散射源。这允许在临床相关的X射线光谱和X射线散射条件下研究探测器的所有特性。使用了真实的焦点（标称0.8 mm）、射束能量（60-100 kVp）和探测器曝光（0.8-2.3 mR），并研究了改变射束尺寸（0-100 cm（2））导致的不同散射分数（0-0.62）的影响。广义MTF和DQE被发现有很小的依赖于管电压和探测器入口曝光。使用焦斑的放大率导致广义DQE在较高频率下大幅降低（在10个周期/mm下约100倍），但在较低频率下显著降低较小。另一方面，散射导致所有频率的广义DQE（散射分数为0.3的因子为3）的恒定下降。我们的研究结果表明，有权衡在不同的系统参数的选择，因此，这种方法的研究成像系统作为一个整体，可以在系统设计提供指导。(C)2005年美国医学物理学家协会。
Detector characterization with modulation transfer function (MTF) and detective quantum efficiency (DQE) inadequately predicts image quality when the imaging system includes focal spot unsharpness and patient scatter. The concepts of MTF, noise power spectrum, noise equivalent quanta and DQE were referenced to the object plane and generalized to include the effect of geometric unsharpness due to the finite size of the focal spot and the effect of the spatial distribution and magnitude of x-ray scatter due to the patient. The generalized quantities provide performance characteristics that consider the complete imaging system, but reduce to a description of the detector properties without magnification or scatter. We have evaluated a new neurovascular angiography imaging system based on a region of interest (ROI) microangiographic detector using these generalized quantities. A uniform head-equivalent phantom was used as a filter and x-ray scatter source. This allowed the study of all properties of the detector under clinically relevant x-ray spectra and x-ray scatter conditions. Realistic focal spots (0.8 mm nominal), beam energies (60-100 kVp), and detector exposures (0.8-2.3 mR) were used, and the effects of different scatter fractions (0-0.62) resulting from changing the beam size (0-100 cm(2)) were investigated. The generalized MTF and DQE were found to have very little dependence on the tube voltage and the detector entrance exposure. Magnification, with the focal spot used, results in a large decrease of the generalized DQE at higher frequencies (about 100-fold at 10 cycles/mm), but a significantly smaller decrease at lower frequencies. Scatter on the other hand, causes a constant drop in the generalized DQE (factor of 3 for scatter fraction 0.3) for all frequencies. Our results show that there are tradeoffs in the choice of the different system parameters; therefore this methodology of studying the imaging system as a whole could provide guidance in system design. (C) 2005 American Association of Physicists in Medicine.