UZ Gasthuisberg, Medical Imaging Research Center and Department of Radiology, Herestraat 49, B-3000 Leuven, Belgium and SCK●CEN, Boeretang 200, B-2400 Mol, Belgium.
Med Phys. 2013 Oct;40(10):101916. doi: 10.1118/1.4820362.
The aim of this paper was to illustrate the value of the new metric effective detective quantum efficiency (eDQE) in relation to more established measures in the optimization process of two digital mammography systems. The following metrics were included for comparison against eDQE: detective quantum efficiency (DQE) of the detector, signal difference to noise ratio (SdNR), and detectability index (d') calculated using a standard nonprewhitened observer with eye filter.
The two systems investigated were the Siemens MAMMOMAT Inspiration and the Hologic Selenia Dimensions. The presampling modulation transfer function (MTF) required for the eDQE was measured using two geometries: a geometry containing scattered radiation and a low scatter geometry. The eDQE, SdNR, and d' were measured for poly(methyl methacrylate) (PMMA) thicknesses of 20, 40, 60, and 70 mm, with and without the antiscatter grid and for a selection of clinically relevant target/filter (T/F) combinations. Figures of merit (FOMs) were then formed from SdNR and d' using the mean glandular dose as the factor to express detriment. Detector DQE was measured at energies covering the range of typical clinically used spectra.
The MTF measured in the presence of scattered radiation showed a large drop at low spatial frequency compared to the low scatter method and led to a corresponding reduction in eDQE. The eDQE for the Siemens system at 1 mm(-1) ranged between 0.15 and 0.27, depending on T/F and grid setting. For the Hologic system, eDQE at 1 mm(-1) varied from 0.15 to 0.32, again depending on T/F and grid setting. The eDQE results for both systems showed that the grid increased the system efficiency for PMMA thicknesses of 40 mm and above but showed only small sensitivity to T/F setting. While results of the SdNR and d' based FOMs confirmed the eDQE grid position results, they were also more specific in terms of T/F selection. For the Siemens system at 20 mm PMMA, the FOMs indicated Mo/Mo (grid out) as optimal while W/Rh (grid in) was the optimal configuration at 40, 60, and 70 mm PMMA. For the Hologic, the FOMs pointed to W/Rh (grid in) at 20 and 40 mm of PMMA while W/Ag (grid in) gave the highest FOM at 60 and 70 mm PMMA. Finally, DQE at 1 mm(-1) averaged for the four beam qualities studied was 0.44 ± 0.02 and 0.55 ± 0.03 for the Siemens and Hologic detectors, respectively, indicating only a small influence of energy on detector DQE.
Both the DQE and eDQE data showed only a small sensitivity to T/F setting for these two systems. The eDQE showed clear preferences in terms of scatter reduction, being highest for the grid-in geometry for PMMA thicknesses of 40 mm and above. The SdNR and d' based figures of merit, which contain additional weighting for contrast and dose, pointed to specific T/F settings for both systems.
本文旨在说明新的有效量子探测效率（eDQE）度量在两种数字乳腺摄影系统优化过程中的价值，该度量与更成熟的度量方法进行了比较。以下度量标准被纳入比较，包括 eDQE：探测器的量子探测效率（DQE）、信号差异噪声比（SdNR）和使用带眼滤光片的标准非预白化观察者计算的检测能力指数（d'）。
研究的两个系统是西门子 MAMMOMAT Inspiration 和豪洛捷 Selenia Dimensions。使用两种几何形状测量了 eDQE 所需的预采样调制传递函数（MTF）：包含散射辐射的几何形状和低散射几何形状。对于聚甲基丙烯酸甲酯（PMMA）厚度为 20、40、60 和 70mm，以及带有和不带有防散射格栅的情况下，测量了 eDQE、SdNR 和 d'，并为选择临床相关的靶/滤光片（T/F）组合进行了测量。然后使用乳腺腺体剂量作为表示损害的因素，从 SdNR 和 d' 形成了优点指标（FOM）。探测器 DQE 在覆盖典型临床使用光谱范围的能量下进行了测量。
与低散射方法相比，在存在散射的情况下测量的 MTF 在低空间频率处显示出较大的下降，导致相应的 eDQE 降低。西门子系统在 1mm^-1 处的 eDQE 范围为 0.15 到 0.27，具体取决于 T/F 和格栅设置。对于豪洛捷系统，在 1mm^-1 处的 eDQE 从 0.15 变化到 0.32，同样取决于 T/F 和格栅设置。两个系统的 eDQE 结果表明，格栅增加了 40mm 及以上 PMMA 厚度的系统效率，但对 T/F 设置的敏感性很小。虽然基于 SdNR 和 d' 的 FOM 结果证实了 eDQE 格栅位置的结果，但它们在 T/F 选择方面也更加具体。对于西门子系统，在 20mm PMMA 处，FOM 表明 Mo/Mo（格栅关闭）为最佳选择，而在 40、60 和 70mm PMMA 处，W/Rh（格栅打开）为最佳配置。对于豪洛捷系统，在 20 和 40mm PMMA 处，FOM 指出 W/Rh（格栅打开）为最佳选择，而在 60 和 70mm PMMA 处，W/Ag（格栅打开）的 FOM 最高。最后，对于研究的四个光束质量，西门子和豪洛捷探测器的 1mm^-1 处的平均 DQE 分别为 0.44 ± 0.02 和 0.55 ± 0.03，这表明能量对探测器 DQE 的影响很小。
对于这两个系统，DQE 和 eDQE 数据仅对 T/F 设置表现出较小的敏感性。eDQE 在降低散射方面表现出明显的偏好，对于 40mm 及以上 PMMA 厚度的格栅内几何形状，eDQE 最高。基于 SdNR 和 d' 的优点指标，其中包含了对比度和剂量的额外权重，针对两个系统指出了特定的 T/F 设置。
