Department of Advanced Technology, Istituto di Ricovero e Cura a Carattere Scientifico, Reggio Emilia, Italy.
Med Phys. 2012 May;39(5):2617-27. doi: 10.1118/1.4704500.
The purpose of this study is to compare digital radiography systems using the metric effective detective quantum efficiency (eDQE), which better reflects digital radiography imaging system performance under clinical operating conditions, in comparison with conventional metrics such as modulation transfer function (MTF), normalized noise power spectra (NNPS), and detective quantum efficiency (DQE).
The eDQE was computed by the calculation of the MTF, the NNPS, the phantom attenuation and scatter, and estimation of x-ray flux. The physical characterization of the systems was obtained with the standard beam conditions RQA5 and RQA9, using the PA Chest phantom proposed by AAPM Report # 31 simulating the attenuation and scatter characteristics of the adult human thorax. The MTF (eMTF) was measured by using an edge test placed at the frontal surface of the phantom, the NNPS (eNNPS) was calculated from images of the phantom acquired at three different exposure levels covering the operating range of the system (E(0), which is the exposure at which a system is normally operated, 1/3 E(0), and 3 E0), and scatter measurements were assessed by using a beam-stop technique. The integral of DQE (IDQE) and eDQE (IeDQE) was calculated over the whole spatial frequency range.
The eMTF results demonstrate degradation due to magnification and the presence of scattered radiation. The eNNPS was influenced by the grid presence, and in some systems, it contained structured noise. At typical clinical exposure levels, the magnitude of eDQE(0) with respect to DQE(0) at RQA9 beam conditions was 13%, 17%, 16%, 36%, and 24%, respectively, for Carestream DRX-1, Carestream DRX-1C, Carestream Direct View CR975, Philips Digital Diagnost VM, and GE Revolution XR/d. These results were confirmed by the ratio of IeDQE and IDQE in the same conditions.
The authors confirm the robustness and reproducibility of the eDQE method. As expected, the DR systems performed better than the CR systems due to their superior signal-to-noise transfer characteristics. The results of this study suggest the eDQE method may provide an opportunity to more accurately assess the clinical performance of digital radiographic imaging systems by accounting for factors such as the presence of scatter, use of an antiscatter grid, and magnification and focal spot blurring effects, which are not reflected in conventional DQE measures.
本研究旨在比较使用有效量子探测效率（eDQE）的数字射线照相系统，与调制传递函数（MTF）、归一化噪声功率谱（NNPS）和量子探测效率（DQE）等传统指标相比，eDQE 更能反映临床操作条件下数字射线照相成像系统的性能。
通过计算 MTF、NNPS、体模衰减和散射以及 X 射线通量估计，计算 eDQE。系统的物理特性通过使用 AAPM 报告 #31 提出的模拟成人胸部衰减和散射特性的 PA 胸部体模在标准光束条件 RQA5 和 RQA9 下获得。使用位于体模前表面的边缘测试测量 MTF（eMTF），从覆盖系统工作范围（E（0）的三个不同曝光水平获取的体模图像中计算 NNPS（eNNPS），E（0）是系统通常操作的曝光水平，1/3 E（0）和 3 E0），并使用束挡技术评估散射测量。在整个空间频率范围内计算 DQE（IDQE）和 eDQE（IeDQE）的积分。
eMTF 结果表明，由于放大和散射辐射的存在，性能会降低。eNNPS 受到网格存在的影响，并且在某些系统中，它包含结构噪声。在典型的临床曝光水平下，Carestream DRX-1、Carestream DRX-1C、Carestream Direct View CR975、Philips Digital Diagnost VM 和 GE Revolution XR/d 在 RQA9 光束条件下的 eDQE（0）与 DQE（0）的比值分别为 13%、17%、16%、36%和 24%。在相同条件下，通过 IeDQE 和 IDQE 的比值证实了这些结果。
作者证实了 eDQE 方法的稳健性和可重复性。正如预期的那样，DR 系统的性能优于 CR 系统，因为它们具有更好的信号噪声传输特性。本研究的结果表明，eDQE 方法可能为更准确地评估数字射线照相成像系统的临床性能提供机会，因为它考虑了散射的存在、使用散射栅以及放大和焦点模糊效应等因素，而这些因素在传统的 DQE 测量中并未反映出来。
