A SPATIAL-FREQUENCY DEPENDENT QUANTUM ACCOUNTING DIAGRAM AND DETECTIVE QUANTUM EFFICIENCY MODEL OF SIGNAL AND NOISE-PROPAGATION IN CASCADED IMAGING-SYSTEMS
A SPATIAL-FREQUENCY DEPENDENT QUANTUM ACCOUNTING DIAGRAM AND DETECTIVE QUANTUM EFFICIENCY MODEL OF SIGNAL AND NOISE-PROPAGATION IN CASCADED IMAGING-SYSTEMS
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DOI：
10.1118/1.597401
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发表时间：
1994-03-01
期刊：
影响因子：
3.8
通讯作者：
FENSTER, A
中科院分区：
文献类型：
--
作者：
CUNNINGHAM, IA;WESTMORE, MS;FENSTER, A
量子探测效率（DQE）是一个系统参数，可以用来准确地描述图像噪声通过许多成像系统的传输特性。一些研究人员使用的一种更简单的方法，特别是在评估新的想法和系统设计时，是将系统描述为一系列级联级。每个阶段可以对应于量子数量的增加（例如，从X射线到射线照相屏幕中的光量子的转换），或者损失（检测或耦合概率）。每个入射初级量子在每个阶段的次级量子的数量由所有先前增益的乘积给出，并且可以图形化地显示以便于解释。具有最少量子的阶段被称为“量子阱”，将像素信噪比限制为小于每个像素量子数的平方根。然而，这种传统的零空间频率“量子计数器”（QAD）忽略了次级量子的空间扩展，并且可能严重低估图像噪声。研究表明，通过引入空间频率相关的QAD（表示为各级增益和平方调制传递函数（MTF）的乘积）可以避免这个问题。一个通用的表达式开发的级联成像系统的DQE是只依赖于增益，增益泊松过剩（相关的方差），和MTF，每一个阶段。一个直接的关系，然后示出之间存在的DQE和QAD中的值。作为一个说明性的例子，QAD的一个假设的系统，包括一个电荷耦合器件的相机和一个闪烁的屏幕进行评估。传统的零频率分析表明，两个量子汇的重要性大致相同：一个是x射线的数量，另一个是光学量子的数量。空间频率相关的分析表明，在非零频率下，光量子阱变得严重并占主导地位。从QAD分析中确定防止感兴趣的空间频率的光量子阱所需的增益或光学数值孔径的必要增加。这种非零空间频率量子阱的视觉影响显示在使用级联过程的蒙特卡罗模拟生成的图像中。
The detective quantum efficiency (DQE) is a system parameter that can be used to accurately describe image noise transfer characteristics through many imaging systems. A simpler approach used by some investigators, particularly when evaluating new ideas and system designs, is to describe the system as a series of cascaded stages. Each stage may correspond to either an increase in the number of quanta (e.g., conversion from x-ray to optical quanta in a radiographic screen), or a loss (a detection or coupling probability). The number of secondary quanta at each stage per incident primary quantum is given by the product of all preceding gains, and can be displayed graphically for convenient interpretation. The stage with the fewest quanta is called the ''quantum sink,'' limiting the pixel signal-to-noise ratio to less than the square root of the number of quanta per pixel. This conventional zero-spatial-frequency ''quantum accounting diagram'' (QAD), however, neglects the spatial spreading of secondary quanta and can seriously underestimate image noise. It is shown that this problem is avoided with the introduction of a spatial-frequency dependent QAD, expressed as the product of the gains and squared modulation-transfer functions (MTF) of each stage. A generalized expression is developed for the DQE of a cascaded imaging system that is dependent only on the gain, gain Poisson excess (related to the variance), and MTF, of each stage. A direct relationship is then shown to exist between the DQE and values in the QAD. The QAD of a hypothetical system consisting of a charge-coupled device camera and a scintillating screen is evaluated as an illustrative example. The conventional zero-frequency analysis suggests two quantum sinks occur with approximately equal importance: one in the number of x rays, and one in the number of optical quanta. The spatial-frequency dependent analysis, however, shows the optical quantum sink becomes severe and dominates at nonzero frequencies. The necessary increase in gain or optical numerical aperture required to prevent the optical quantum sink for spatial frequencies of interest is determined from the QAD analysis. The visual impact of this nonzero spatial-frequency quantum sink is shown in images generated using a Monte Carlo simulation of the cascading process.