Department of Medical Physics, University of Wisconsin-Madison, 1111 Highland Avenue, Madison, WI 53705, United States of America.
Department of Radiology, University of Wisconsin-Madison, 600 Highland Avenue, Madison, WI 53792, United States of America.
Phys Med Biol. 2019 Apr 4;64(7):075013-75013. doi: 10.1088/1361-6560/ab10a2.
The zero-frequency detective quantum efficiency (DQE), viz., DQE, is defined as the ratio between output and input squared signal-to-noise ratio of an imaging system. In 1963, R. Shaw applied Fourier analysis to generalize DQE to the frequency-dependent DQE, i.e. DQE[Formula: see text]. Under conditions specified by Shaw, DQE[Formula: see text] is the same as DQE at k = 0. The experimental measurement of DQE[Formula: see text] involves the measurement of system modulation transfer function (MTF) and noise power spectrum (NPS). Although the measurement of MTF is straightforward, the experimental measurements of NPS[Formula: see text] encountered several challenges. As a result, some experimental methods may yield a nonphysical NPS value at k = 0, which makes the measured DQE(k)| deviate from the true zero-frequency DQE. This work presents new results from three aspects: 1) system drift is a significant error source when a large number of independent image acquisitions are involved in measuring NPS and DQE; 2) a cascaded systems analysis shows that the drift induces a global positive offset to the measured autocovariance function, and the offset is quantitatively related to the NPS error at k = 0; 3) based on the measured autocovariance data, drift-induced offset can be estimated, so that errors in the measured NPS(k)| and DQE(k)| can be corrected. Both numerical simulations with known ground truth for DQE and experimental studies were performed to validate the proposed measurement method. The results demonstrated that the method mitigates the undesirable influence of system drift in DQE(k)| and DQE, allowing the measured values consistent with the classical definition of zero-frequency DQE.
零频率探测量子效率（DQE），即 DQE，定义为成像系统的输出与输入平方信噪比之比。1963 年，R. Shaw 应用傅里叶分析将 DQE 推广到频率相关的 DQE，即 DQE[公式：见文本]。在 Shaw 规定的条件下，DQE[公式：见文本]与 k=0 时的 DQE 相同。DQE[公式：见文本]的实验测量涉及系统调制传递函数（MTF）和噪声功率谱（NPS）的测量。虽然 MTF 的测量很直接，但 NPS[公式：见文本]的实验测量遇到了几个挑战。因此，一些实验方法可能会在 k=0 时产生非物理的 NPS 值，这使得测量的 DQE(k)|偏离真实的零频率 DQE。这项工作从三个方面提出了新的结果：1）当涉及大量独立图像采集来测量 NPS 和 DQE 时，系统漂移是一个重要的误差源；2）级联系统分析表明，漂移会导致测量自协方差函数产生全局正偏移，并且该偏移与 k=0 时的 NPS 误差定量相关；3）基于测量的自协方差数据，可以估计漂移引起的偏移，从而校正测量的 NPS(k)|和 DQE(k)|中的误差。对具有已知 DQE 真实值的数值模拟和实验研究都进行了验证，结果表明，该方法减轻了 DQE(k)|和 DQE 中系统漂移的不良影响，使测量值与零频率 DQE 的经典定义一致。
