Department of Radiology, University of Iowa Hospitals and Clinics, 200 Hawkins Drive, Iowa City, IA, 52242, USA.
Department of Biomedical Engineering, University of Iowa, 1402 Seamans Center, Iowa City, IA, 52242, USA.
Med Phys. 2017 Sep;44(9):4747-4757. doi: 10.1002/mp.12436. Epub 2017 Aug 2.
Quantitative computed tomography (CT) measures are increasingly being developed and used to characterize lung disease. With recent advances in CT technologies, we sought to evaluate the quantitative accuracy of lung imaging at low- and ultralow-radiation doses with the use of iterative reconstruction (IR), tube current modulation (TCM), and spectral shaping.
We investigated the effect of five independent CT protocols reconstructed with IR on quantitative airway measures and global lung measures using an in vivo large animal model as a human subject surrogate. A control protocol was chosen (NIH-SPIROMICS + TCM) and five independent protocols investigating TCM, low- and ultralow-radiation dose, and spectral shaping. For all scans, quantitative global parenchymal measurements (mean, median and standard deviation of the parenchymal HU, along with measures of emphysema) and global airway measurements (number of segmented airways and pi10) were generated. In addition, selected individual airway measurements (minor and major inner diameter, wall thickness, inner and outer area, inner and outer perimeter, wall area fraction, and inner equivalent circle diameter) were evaluated. Comparisons were made between control and target protocols using difference and repeatability measures.
Estimated CT volume dose index (CTDIvol) across all protocols ranged from 7.32 mGy to 0.32 mGy. Low- and ultralow-dose protocols required more manual editing and resolved fewer airway branches; yet, comparable pi10 whole lung measures were observed across all protocols. Similar trends in acquired parenchymal and airway measurements were observed across all protocols, with increased measurement differences using the ultralow-dose protocols. However, for small airways (1.9 ± 0.2 mm) and medium airways (5.7 ± 0.4 mm), the measurement differences across all protocols were comparable to the control protocol repeatability across breath holds. Diameters, wall thickness, wall area fraction, and equivalent diameter had smaller measurement differences than area and perimeter measurements.
In conclusion, the use of IR with low- and ultralow-dose CT protocols with CT volume dose indices down to 0.32 mGy maintains selected quantitative parenchymal and airway measurements relevant to pulmonary disease characterization.
定量计算机断层扫描（CT）测量方法越来越多地被开发和用于描述肺部疾病。随着 CT 技术的最新进展，我们试图评估使用迭代重建（IR）、管电流调制（TCM）和光谱成形的低剂量和超低剂量 CT 成像的定量准确性。
我们使用体内大动物模型作为人体替代物，研究了 IR 重建的五种独立 CT 协议对定量气道测量和整体肺测量的影响。选择了一个对照协议（NIH-SPIROMICS+TCM）和五个独立协议，分别研究 TCM、低剂量和超低剂量以及光谱成形。对于所有扫描，生成了定量的整体实质测量值（实质 HU 的平均值、中位数和标准差，以及肺气肿的测量值）和整体气道测量值（分段气道数量和 pi10）。此外，还评估了选定的单个气道测量值（小直径和大直径、壁厚度、内区和外区、内区和外区周长、壁区分数和内等效圆直径）。使用差值和重复性测量值对对照和目标协议进行比较。
所有协议的估计 CT 体积剂量指数（CTDIvol）范围从 7.32mGy 到 0.32mGy。低剂量和超低剂量协议需要更多的手动编辑，解决的气道分支较少；然而，所有协议的 pi10 全肺测量值相似。所有协议中观察到相似的实质和气道测量值变化趋势，使用超低剂量协议时测量值差异更大。然而，对于小气道（1.9±0.2mm）和中等气道（5.7±0.4mm），所有协议的测量值差异与呼吸暂停时的对照协议重复性相当。直径、壁厚度、壁区分数和等效直径的测量值差异小于面积和周长测量值。
总之，使用低剂量和超低剂量 CT 协议与 CT 体积剂量指数低至 0.32mGy 的 IR 可以维持与肺部疾病特征相关的选定定量实质和气道测量值。
