Fisica Sanitaria, Azienda Ospedaliero Universitaria Careggi, viale Pieraccini 17 - Firenze, FI 50139 Italy.
Med Phys. 2007 Jul;34(7):2730-43. doi: 10.1118/1.2742498.
The purpose of this study was to evaluate and compare the physical characteristics of five clinical systems for digital mammography (GE Senographe 2000D, Lorad Selenia M-IV, Fischer Senoscan, Agfa DM 1000, and IMS Giotto) currently in clinical use. The basic performances of the mammography systems tested were assessed on the basis of response curve, modulation transfer function (MTF), noise power spectrum, noise equivalent quanta (NEQ), and detective quantum efficiency (DQE) in an experimental setting closely resembling the clinical one. As expected, all the full field digital mammography systems show a linear response curve over a dynamic range from 3.5 to 500 microGy (0.998<R2< 1). The presampling MTFs at 2, 3, and 5 lp/mm were found to be respectively 0.78, 0.64, and 0.37 for GE Senographe 2000D; 0.92, 0.85, and 0.69 for Lorad Selenia and Agfa DM1000; 0.75, 0.63, and 0.42 for Fischer Senoscan; and 0.91, 0.82, and 0.61 for the IMS Giotto. According to the pixel size of each digital system, the presampling MTF was calculated within a range up to the Nyquist frequency (5 lp/mm for GE Senographe 2000D, 7.1 lp/mm for Lorad Selenia, 9.3 lp/mm for Fischer Senoscan, and 5.88 lp/mm for IMS Giotto detector). The NEQ becomes related to the exposure in a linear behavior starting from about 40.3 microGy for GE Senographe 2000D, 42.9 microGy for Lorad Selenia, 41.2 microGy for Agfa DM1000, <87.6 microGy for Fischer Senoscan, and 61.3 microGy for the IMS Giotto. Above those values, the systems can be considered "quantum noise limited," that is the electronic noise is negligible if compared to the quantum noise. The DQE, for several emitted x-ray spectra for each system, i.e., 28 kV p Mo-Mo, Mo-Rh, Rh-Rh, W-Al anode-filter combination, hardened by 40 mm poly(methylmethacrylate) (PMMA) was evaluated. For the five different systems, the DQE at close to zero spatial frequency ranges between 0.25 and 0.63 at 131 microGy entrance surface air kerma to the detectors. The results of our quantitative analysis demonstrated a higher DQE for direct conversion technology when compared to that of the indirect conversion. The NEQ behavior of each system can be exploited to select the optimum exposure level set in clinical practice to ensure minimum patient dose though adequate image quality. The detailed results of the physical characterization of the digital systems reported in this work allow the quantitative comparison of different technologies as well as the definition of reference values for subsequent quality control tests. The method developed in this work is suitable to be reproduced in any medical physics department for the previously described goals.
本研究旨在评估和比较目前临床使用的五种数字乳腺摄影临床系统（GE Senographe 2000D、Lorad Selenia M-IV、Fischer Senoscan、Agfa DM 1000 和 IMS Giotto）的物理特性。在与临床环境非常相似的实验环境中，根据响应曲线、调制传递函数（MTF）、噪声功率谱、噪声等效量子（NEQ）和检测量子效率（DQE）对乳腺摄影系统的基本性能进行评估。正如预期的那样，所有全视野数字乳腺摄影系统在 3.5 至 500 μGy 的动态范围内均显示出线性响应曲线（0.998<R2<1）。在 2、3 和 5 lp/mm 处的预采样 MTF 分别为：GE Senographe 2000D 为 0.78、0.64 和 0.37；Lorad Selenia 和 Agfa DM1000 为 0.92、0.85 和 0.69；Fischer Senoscan 为 0.75、0.63 和 0.42；而 IMS Giotto 为 0.91、0.82 和 0.61。根据每个数字系统的像素大小，在奈奎斯特频率（GE Senographe 2000D 为 5 lp/mm，Lorad Selenia 为 7.1 lp/mm，Fischer Senoscan 为 9.3 lp/mm，IMS Giotto 为 5.88 lp/mm）以下的范围内计算预采样 MTF。NEQ 从大约 40.3 μGy（GE Senographe 2000D）、42.9 μGy（Lorad Selenia）、41.2 μGy（Agfa DM1000）开始，以线性方式与曝光相关，对于 Fischer Senoscan <87.6 μGy，而对于 IMS Giotto 为 61.3 μGy。在这些值以上，系统可以被认为是“量子噪声限制”，即与量子噪声相比，电子噪声可以忽略不计。对于每个系统的几个发射 X 射线光谱（28 kV p Mo-Mo、Mo-Rh、Rh-Rh、W-Al 阳极滤光片组合，由 40 mm 聚甲基丙烯酸甲酯（PMMA）硬化），评估了 DQE。对于五个不同的系统，在接近零空间频率的范围内，DQE 在 131 μGy 入射到探测器的表面空气比释动能时为 0.25 至 0.63。我们的定量分析结果表明，与间接转换相比，直接转换技术具有更高的 DQE。每个系统的 NEQ 行为可用于选择临床实践中的最佳曝光水平，以确保在适当的图像质量下，患者接受的剂量最小。本工作中报告的数字系统的物理特性的详细结果允许对不同技术进行定量比较，并为随后的质量控制测试定义参考值。本工作中开发的方法适用于任何医学物理部门，以实现上述目标。
