Department of Radiology, Cochin Hospital, AP-HP Centre, 75014 Paris, France; Diagnostic and Interventional Radiology, University Hospital Zurich, 8008 Zurich, Switzerland.
Department of Radiology, Cochin Hospital, AP-HP Centre, 75014 Paris, France.
Diagn Interv Imaging. 2020 May;101(5):269-279. doi: 10.1016/j.diii.2020.01.012. Epub 2020 Feb 24.
The purpose of this study was to analyze the impact of different options for reduced-dose computed tomography (CT) on image noise and visibility of pulmonary structures in order to define the best choice of parameters when performing ultra-low dose acquisitions of the chest in clinical routine.
Using an anthropomorphic chest phantom, CT images were acquired at four defined low dose levels (computed tomography dose index [CTDI]=0.15, 0.20, 0.30 and 0.40mGy), by changing tube voltage, pitch factor, or rotation time and adapting tube current to reach the predefined CTDI-values. Images were reconstructed using two different levels of iteration (adaptive statistical iterative reconstruction [ASIR®]-v70% and ASIR®-v100%). Signal-to-noise ratio (SNR) as well as contrast-to-noise ratio (CNR) was calculated. Visibility of pulmonary structures (bronchi/vessels) were assessed by two readers on a 5-point-Likert scale.
Best visual image assessments and CNR/SNR were obtained with high tube voltage, while lowest scores were reached with lower pitch factor followed by high tube current. Protocols favoring lower pitch factor resulted in decreased visibility of bronchi/vessels, especially in the periphery. Decreasing radiation dose from 0.40 to 0.30mGy was not associated with a significant decrease in visual scores (P<0.05), however decreasing radiation dose from 0.30mGy to 0.15mGy was associated with a lower visibility of most of the evaluated structures (P<0.001). While image noise could be significantly reduced when ASIR®-v100% instead of ASIR®-v70% was used, the visibility-scores of pulmonary structures did not change significantly.
Favoring high tube voltage is the best option for reduced-dose protocols. A decrease of SNR and CNR does not necessarily go along with reduced visibility of pulmonary structures.
本研究旨在分析不同低剂量 CT 方案对肺部结构图像噪声和可视性的影响，以便在临床常规中进行超低剂量胸部 CT 扫描时确定最佳参数选择。
使用人体胸部体模，通过改变管电压、螺距因子或旋转时间，并调整管电流以达到预设的 CTDI 值，在四个定义的低剂量水平（CTDI=0.15、0.20、0.30 和 0.40mGy）下采集 CT 图像。使用两种不同迭代水平（自适应统计迭代重建[ASIR®]-v70%和 ASIR®-v100%）进行图像重建。计算信噪比（SNR）和对比噪声比（CNR）。由两位读者对肺结构（支气管/血管）的可视性进行 5 分制评分。
高管电压获得最佳的视觉图像评估和 CNR/SNR，而低螺距因子和高管电流则获得最低的评分。有利于低螺距因子的方案导致支气管/血管的可视性降低，特别是在周边区域。从 0.40mGy 降低至 0.30mGy 的辐射剂量不会导致视觉评分显著降低（P<0.05），但从 0.30mGy 降低至 0.15mGy 会导致大多数评估结构的可视性降低（P<0.001）。当使用 ASIR®-v100%替代 ASIR®-v70%时，图像噪声可以显著降低，但肺结构的可视性评分没有显著变化。
选择高管电压是低剂量方案的最佳选择。信噪比和对比噪声比的降低不一定伴随着肺部结构可视性的降低。
