Department of Radiation Physics, University of Gothenburg, SE-413 45 Gothenburg, Sweden.
Med Phys. 2010 Jan;37(1):258-69. doi: 10.1118/1.3273064.
Methods for simulating dose reduction are valuable tools in the work of optimizing radiographic examinations. Using such methods, clinical images can be simulated to have been collected at other, lower, dose levels without the need of additional patient exposure. A recent technology introduced to healthcare that needs optimization is tomosynthesis, where a number of low-dose projection images collected at different angles is used to reconstruct section images of an imaged object. The aim of the present work was to develop a method of simulating dose reduction for digital radiographic systems, suitable for tomosynthesis.
The developed method uses information about the noise power spectrum (NPS) at the original dose level and the simulated dose level to create a noise image that is added to the original image to produce an image that has the same noise properties as an image actually collected at the simulated dose level. As the detective quantum efficiency (DQE) of digital detectors operating at the low dose levels used for tomosynthesis may show a strong dependency on the dose level, it is important that a method for simulating dose reduction for tomosynthesis takes this dependency into account. By applying an experimentally determined relationship between pixel mean and pixel variance, variations in both dose and DQE in relevant dose ranges are taken into account.
The developed method was tested on a chest tomosynthesis system and was shown to produce NPS of simulated dose-reduced projection images that agreed well with the NPS of images actually collected at the simulated dose level. The simulated dose reduction method was also applied to tomosynthesis examinations of an anthropomorphic chest phantom, and the obtained noise in the reconstructed section images was very similar to that of an examination actually performed at the simulated dose level.
In conclusion, the present article describes a method for simulating dose reduction suitable for tomosynthesis. However, the method applies equally well to any digital radiographic system, although the benefits of correcting for DQE variations may be smaller.
模拟剂量减少的方法是优化放射学检查工作的有价值的工具。使用这些方法，可以模拟临床图像，使其看起来像是在其他较低剂量水平下采集的，而无需对患者进行额外的照射。最近引入医疗保健领域的一种需要优化的技术是断层合成术，其中使用在不同角度采集的多个低剂量投影图像来重建被成像物体的截面图像。本工作的目的是开发一种适用于断层合成术的数字放射系统的剂量减少模拟方法。
所开发的方法使用原始剂量水平和模拟剂量水平的噪声功率谱（NPS）信息来创建噪声图像，该噪声图像被添加到原始图像中，以生成具有与实际在模拟剂量水平下采集的图像相同的噪声特性的图像。由于断层合成术所使用的低剂量水平下工作的数字探测器的探测量子效率（DQE）可能强烈依赖于剂量水平，因此模拟断层合成术剂量减少的方法必须考虑到这种依赖性。通过应用在剂量相关范围内像素均值和像素方差之间的实验确定的关系，可以考虑剂量和 DQE 的变化。
所开发的方法在胸部断层合成系统上进行了测试，结果表明，模拟剂量减少的投影图像的 NPS 与实际在模拟剂量水平下采集的图像的 NPS 非常吻合。还将模拟剂量减少方法应用于人体胸部模拟体模的断层合成检查，并且在重建的截面图像中获得的噪声与在模拟剂量水平下实际进行的检查非常相似。
总之，本文描述了一种适用于断层合成术的剂量减少模拟方法。然而，该方法同样适用于任何数字放射系统，尽管校正 DQE 变化的好处可能较小。
