The influence of reconstruction algorithm on the measurement of airway dimensions using computed tomography

The assessment of airway dimensions is important in understanding the pathophysiology of various lung diseases. A number of methods have been developed to measure airways on computed tomography, but no study has been done to validate the different CT scanning techniques, CT scanners, and reconstruction algorithms. In our study, we constructed an artificial "airway" and "lung" phantom using hollow plastic tubes and foam blocks. The phantom was CT scanned using axial or helical techniques, and the images were reconstructed using a very high spatial frequency algorithm, a high spatial frequency algorithm, or a low spatial frequency algorithm. Custom software was then used to analyze the "airways" and measure lumen area (Ai) and "airway" wall area (Aaw). WA% (WA% = 100 x Aaw / (Ai + Aaw)) was also calculated. The cross-sectional area of the lumen and wall of the plastic tubes were measured using an optical micrometer. CT measurements of airway dimensions were virtually identical, comparing axial and helical techniques, and comparing a single-slice CT scanner to a multi-slice CT scanner. Using the plastic tube measurements as a "gold standard", Ai was estimated better with the very high or high spatial frequency algorithm (4.1 and 7.4 % error) vs. low spatial frequency algorithm (10.4% error). Aaw was better estimated with the low or high special frequency algorithm (3.8% and 6.1 %) vs. very high spatial frequency algorithm (12.9%), and WA% was better estimated with the high or low spatial frequency algorithm (3.5% and 5.1%) vs. very high spatial frequency algorithm (7.3%). Based on these results, we recommend the high spatial frequency algorithm for the CT measurement of airway dimensions.