Department of Radiological Sciences, University of California Irvine, Irvine, CA, USA.
Department of Radiology, University of California Davis, Sacramento, CA, USA.
Med Phys. 2021 Oct;48(10):5874-5883. doi: 10.1002/mp.15103. Epub 2021 Aug 18.
Small airways with inner diameters less than 2 mm are sites of major airflow limitations in patients with chronic obstructive pulmonary disease (COPD) and asthma. The purpose of this study is to investigate the limitations for accurate assessment of small airway dimensions using both high-resolution CT (HRCT) and conventional normal-resolution CT at low dose levels.
To model the normal human airways from the 3rd to 20th generations, a cylindrical polyurethane phantom with 14 airway tubes of inner diameters (ID) ranging from 0.3 to 3.4 mm and wall thicknesses (WT) ranging from 0.15 to 1.6 mm was placed within an Anthropomorphic QRM-Thorax phantom. The Aquilion Precision (Canon Medical Systems Corporation) HRCT scanner was used to acquire images at 80, 100, and 120 kV using high resolution mode (HR, 0.25 mm × 160 detector configuration) and normal-resolution (NR) mode (0.5 mm × 80 detector configuration). The HR data were reconstructed using a 1024 × 1024 matrix (0.22 × 0.22 × 0.25 mm voxel size) and the NR data were reconstructed using a 512 × 512 matrix (0.43 × 0.43 × 0.50 mm). Two reconstruction algorithms (filtered back projection; FBP and an adaptive iterative dose reduction 3D algorithm; AIDR 3D) and three reconstruction kernels (FC30, FC52, and FC56) were investigated. The dose values ranged from 0.2 to 6.2 mGy. A refined automated full-width half-maximum (FWHM) method was used for the measurement of airway dimensions, where the density profiles were computed by radial oversampling using a polar coordinate system. Both ID and WT were compared to the known dimensions using a regression model, and the root-mean-square error (RMSE) and average error were computed across all 14 airway tubes.
The results indicate that the ID can be measured within a 15% error down to approximately 0.8 and 2.0 mm using the HR and NR modes, respectively. The overall RMSE (and average error) of ID measurements for HR and NR were 0.10 mm (-0.70%) and 0.31 mm (-2.63%), respectively. The RMSE (and average error) of WT measurements using HR and NR were 0.10 mm (23.27%) and 0.27 mm (53.56%), respectively. The WT measurement using HR yielded a factor of two improvement in accuracy as compared to NR.
High-resolution CT can provide more accurate measurements of airway dimensions as compared with NR CT, potentially improving quantitative assessment of pathologies such as COPD and asthma. The HR mode acquired and reconstructed with AIDR3D and the FC52 kernel provides most accurate measurement of airway dimensions. Low-dose HR measurements at dose level above 0.9 mGy can provide improved accuracy on both inner diameters and wall thicknesses compared to full dose NR airway phantom measurements.
内径小于 2 毫米的小气道是慢性阻塞性肺疾病（COPD）和哮喘患者气流受限的主要部位。本研究旨在探讨高分辨率 CT（HRCT）和低剂量常规标准分辨率 CT （NRCT）在准确评估小气道尺寸方面的局限性。
为了模拟第 3 至 20 代正常人类气道，将内径（ID）范围为 0.3 至 3.4 毫米和壁厚（WT）范围为 0.15 至 1.6 毫米的 14 个气道管的圆柱形聚氨酯体模置于人体形态 QRM-Thorax 体模内。使用 Aquilion Precision（佳能医疗系统公司）HRCT 扫描仪以高分辨率模式（HR，0.25 毫米×160 探测器配置）和标准分辨率模式（NR，0.5 毫米×80 探测器配置）在 80、100 和 120kV 下采集图像。HR 数据使用 1024×1024 矩阵（0.22×0.22×0.25 毫米体素大小）重建，NR 数据使用 512×512 矩阵（0.43×0.43×0.50 毫米）重建。研究了两种重建算法（滤波反投影；FBP 和自适应迭代剂量降低 3D 算法；AIDR 3D）和三种重建核（FC30、FC52 和 FC56）。剂量值范围为 0.2 至 6.2mGy。使用改进的自动全宽半最大值（FWHM）方法进行气道尺寸测量，其中密度分布通过使用极坐标系统的径向过采样来计算。使用回归模型将 ID 和 WT 与已知尺寸进行比较，并计算所有 14 个气道管的均方根误差（RMSE）和平均误差。
结果表明，使用 HR 和 NR 模式，内径可在 15%的误差范围内测量到约 0.8 和 2.0 毫米。HR 和 NR 对 ID 测量的总体 RMSE（和平均误差）分别为 0.10 毫米（-0.70%）和 0.31 毫米（-2.63%）。使用 HR 和 NR 对 WT 测量的 RMSE（和平均误差）分别为 0.10 毫米（23.27%）和 0.27 毫米（53.56%）。与 NR 相比，HR 对 WT 的测量精度提高了两倍。
与 NR CT 相比，高分辨率 CT 可以提供更准确的气道尺寸测量值，可能会改善 COPD 和哮喘等疾病的定量评估。使用 AIDR3D 采集和重建的 HR 模式以及 FC52 核提供了最准确的气道尺寸测量值。与全剂量 NR 气道体模测量相比，剂量水平高于 0.9mGy 的低剂量 HR 测量可在内径和壁厚方面提供更好的准确性。
