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

Abstract

PURPOSE\nDisease in small airways <2\u2009mm in diameter is a major pathology of chronic obstructive pulmonary disease (COPD). However, compared to airways <1\u2009mm in diameter, the pathophysiological role of airways 1-2\u2009mm 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.\n\n\nMETHOD\nThe 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\u2009×\u20091024 matrix, 0.25\u2009mm slice thickness) and spirometry, all 3rd (segmental) to 6th generation airways of the right apical and basal posterior bronchus (RB1 and RB10) were analysed.\n\n\nRESULTS\nThe errors in measuring the lumen area (LA) of phantom tubes ≥1.3 and 1.0\u2009mm 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\u2009mm. 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.\n\n\nCONCLUSIONS\nU-HRCT enables accurate and direct evaluation of peripheral airways 1-2\u2009mm in diameter. The 6th generation airways are commonly <2\u2009mm in diameter, and the sum-LA can be a useful CT biomarker that reflects airflow limitation in COPD.