The mean values of CT density (HU) in the phantom materials mimicking lung parenchyma and the mean values of maximum CT density in the tube walls.

<p>Average of measured values (SD).</p

Schema describing the method of airway dimension measurement.

<p>A: Using sequential CT slices which included a section of the target tube, the center (solid) line of the tube was calculated by linking the center points of sections on each slice. B: Images were constructed perpendicular to the center line.</p

Effects of scanning conditions on errors of airway dimension measurement.

<p>A: Effects of field of view (FOV) and slice thickness on errors for wall area percentage (WA%) in acrylic resin tubes surrounded by acrylic foam that were scanned using Aquilion 64 (120 mAs and lung algorithm FC56). B: Effects of the reconstruction algorithm on the errors of WA% in acrylic resin tubes surrounded by acrylic foam that were scanned using Aquilion 64 (120 mAs, 0.5-mm slice thickness, 350-mm FOV). FC13: body algorithm, FC51: lung algorithm, FC56: lung algorithm (FC51) with beam-hardening correction. *: failure to measure. The error of airway dimensions was defined as follows: Error (%) = (CT measurement − actual value)/actual value×100.</p

Effects of phantom composition on errors of airway dimension measurement.

<p>Percentage error of wall area (WA%) and luminal area (Ai) for the phantom scanned using Aquilion 64 (120 mAs, 0.5-mm slice thickness, 350-mm FOV, lung reconstruction algorithm FC56). A: Comparison of errors of WA% and Ai for acrylic resin tubes among materials simulating lung parenchyma, phenol resin (0.32 g/cm³), acrylic foam (0.10 g/cm³), and air. B: Comparison of errors for WA% and Ai among tube materials, fluorocarbon polymers (2.1 g/cm³), acrylic resin (1.2 g/cm³), and polyethylene (0.9 g/cm³) embedded in acrylic foam.</p

Effects of wall thickness on airway dimension measurement.

<p>Average of measured values (SD).</p><p>Measured values of Ai, WA%, and wall thickness (WT) for various wall thickness using airway phantom B (actual luminal area: 7.07 mm²) scanned by Aquilion 64 (120 mAs, 0.5-mm slice thickness, 350-mm FOV, and lung reconstruction algorithm FC56).</p

Effects of CT scanner and FOV on errors of airway dimension measurement.

<p>Comparison of errors WA% and luminal area (Ai) in acrylic resin tubes embedded in acrylic foam among four CT scanners under varying FOV (A: 200 mm, B: 350 mm). The images were reconstructed by the lung algorithm. The definition of error is shown in the legend to <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0076381#pone-0076381-g003" target="_blank">Figure 3</a>.</p

The four CT scanners used in assessments and their respective scanning data.

<p>kVp, kilovolts peak; FOV, field of view; AEC, automatic exposure control (actual range in this study: 25–30 mAs).</p

Effects of phantom angles on errors of airway dimension measurement.

<p>Percent errors from actual value (SD).</p><p>Errors of WA% in acrylic resin tubes embedded in acrylic foam at various angles using Aquilion 64 (120 mAs, 0.5-mm slice thickness, 350-mm FOV, lung reconstruction algorithm FC56).</p

Examples of airways measured at different generations.

<p>The representative images of right posterior basal bronchi (3^rd generation) and more distal bronchi of a healthy control on Aquilion 64 (Auto Exposure Control, 0.5-mm slice thickness, 350-mm FOV, lung reconstruction algorithm FC56). At the 6^th to 7^th generation, the thickness of the bronchus wall had equal or less than pixels size.</p

Axial slice computed tomography (CT) image of phantom A.

<p>The inner space of the cylindrical container is filled with successive layers of three materials: phenol resin, acrylic foam, and air. A total of 18 tubes (three materials×six sizes) were embedded through each layer (50 or 60 mm in length).</p