Direct evaluation of peripheral airways using ultra-high-resolution CT in chronic obstructive pulmonary disease

Abstract

PurposeDisease in small airways <2 mm in diameter is a major pathology of chronic obstructive pulmonary disease (COPD). However, compared to airways <1 mm in diameter, the pathophysiological role of airways 1–2 mm in diameter remains unclear. This study analysed phantom and human COPD data to test the hypothesis that ultra-high-resolution computed tomography (U-HRCT) can accurately measure peripheral airways that are difficult to measure with conventional CT. MethodThe lower limit of lumen sizes measurable on U-HRCT was determined using phantom tubes. In the cross-sectional data of 110 males with COPD who underwent U-HRCT (1024 × 1024 matrix, 0.25 mm slice thickness) and spirometry, all 3rd (segmental) to 6th generation airways of the right apical and basal posterior bronchus (RB1 and RB10) were analysed. ResultsThe errors in measuring the lumen area (LA) of phantom tubes ≥1.3 and 1.0 mm in diameter were within ±10 and -24%, respectively. The internal diameters for 70 and 62% of the 6th generation RB1 and RB10 airways were <2 mm. The numbers of 6th generation RB1 and RB10 airways decreased as the airflow limitation severity increased. Among the mean LA and sum of LA(sum-LA) of the 3rd to 6th generation airways, the sum-LA of the 6th generation had the largest impact on airflow limitation. ConclusionsU-HRCT enables accurate and direct evaluation of peripheral airways 1–2 mm in diameter. The 6th generation airways are commonly <2 mm in diameter, and the sum-LA can be a useful CT biomarker that reflects airflow limitation in COPD.