Quantitative Thin-Section CT Analysis of the Enlargement and Coalescence of Low-Attenuation Clusters in Patients with Emphysema

Abstract

Background: The analysis of the number and size of low-attenuation clusters has been adopted as quantitative computed tomography (CT) analysis of emphysema; however, a detailed examination has not been made on the relation between the number of various cluster sizes and the extent of emphysema. Objective: The aim of this study was to evaluate the relationship between the size and number of clusters on CT scans in patients with emphysema. Methods: This retrospective study included 31 emphysema patients. The number (LAN) and mean size (LAS) of clusters below –950 HU, and relative low-attenuation area below –950 HU (RA950) were calculated using an image-processing program. The size of clusters was divided into 3 categories, and the number in each size category was obtained as follows: small (sLAN 0.4–8 mm²), medium (mLAN 8.4–40 mm²), and large (lLAN >40 mm²). The relationships between the RA950 and sLAN, mLAN, or lLAN were evaluated. Patients were divided according to the extent of RA950 (>25% = severe emphysema, <25% = mild emphysema), and the relations between RA950 and LAN, and between RA950 and sLAN, mLAN, or lLAN were evaluated. Results: The sLAN decreased as RA950 increased (r = –0.477), whereas mLAN and lLAN increased (r = 0.421, and r = 0.819). In severe emphysema, sLAN and mLAN decreased as RA950 increased (r = –0.722, and r = –0.698). In mild emphysema, mLAN and lLAN increased as RA950 increased (r = 0.732, and r = 0.972). Conclusions: The degree of the coalescence of the clusters depends on the size of clusters and the extent of emphysema. Quantitative CT analyses of clusters are helpful to elucidate the pathophysiology and progressive nature of emphysema.