Yang Zepa, Jin Hyeongmin, Kim Jong Hyo
Program in Biomedical Radiation Sciences, Graduate School of Convergence Science and Technology, Seoul National University, Seoul, 08826, Korea.
Department of Radiology, Seoul National University Hospital, Seoul, 03080, Korea.
Med Phys. 2018 Jul 3. doi: 10.1002/mp.13074.
The dimensions of small airways with an internal diameter of less than 2-3 mm are important biomarkers for the evaluation of pulmonary diseases, such as asthma and chronic obstructive pulmonary disease (COPD). The resolution limitations of CT systems, however, have remained a barrier to be of use for determining the small airway dimensions. We present a novel approach, called the attenuation profile matching (APM) method, which allows for the accurate determination of the small airway dimension while being robust to varying CT scan parameters.
For generating the synthetic attenuation profiles of an airway, we acquired and employed the point spread functions of a CT system by calculating its convolution with numerical airway models with varying wall thicknesses. The dimensions of a given airway were determined as per the numerical model yielding minimum error between the measured and the synthetic attenuation profiles across the airway.
In a phantom study with airway tubes, the APM method proved to be highly accurate in determining airway wall dimensions. The measurement error for the smallest tube (0.6 mm thickness, 3 mm diameter) was merely 0.02 mm (3.3%) in wall thickness and 0.17 mm (5.6%) in lumen diameter. In a pilot clinical test, the APM method was able to distinguish the airway wall thicknesses of COPD cases (1.16 ± 0.23 mm) from those of normal subjects (0.6 ± 0.18 mm), while the measurements using the full width at half maximum method substantially overlapped (1.45 ± 0.32 mm vs. 1.28 ± 0.30 mm, respectively) and were barely distinguishable from each other.
Our proposed APM method has the potential to overcome the resolution limitations of current CT systems and accurately determine the small airway dimensions in COPD patients.
内径小于2 - 3毫米的小气道尺寸是评估肺部疾病（如哮喘和慢性阻塞性肺疾病（COPD））的重要生物标志物。然而，CT系统的分辨率限制一直是确定小气道尺寸的障碍。我们提出了一种名为衰减轮廓匹配（APM）方法的新方法，该方法能够准确确定小气道尺寸，同时对不同的CT扫描参数具有鲁棒性。
为了生成气道的合成衰减轮廓，我们通过计算CT系统的点扩散函数与具有不同壁厚的数值气道模型的卷积来获取并应用该函数。根据数值模型确定给定气道的尺寸，该模型在整个气道上使测量的和合成的衰减轮廓之间的误差最小。
在气道管模体研究中，APM方法在确定气道壁尺寸方面被证明具有高度准确性。最小管（壁厚0.6毫米，直径3毫米）的壁厚测量误差仅为0.02毫米（3.3%），管腔直径测量误差为0.17毫米（5.6%）。在一项初步临床试验中，APM方法能够区分COPD病例的气道壁厚度（1.16±0.23毫米）与正常受试者的气道壁厚度（0.6±0.18毫米），而使用半高宽法的测量结果基本重叠（分别为1.45±0.32毫米和1.28±0.30毫米），且彼此几乎无法区分。
我们提出的APM方法有潜力克服当前CT系统的分辨率限制，并准确确定COPD患者的小气道尺寸。
