Semi-Automatic Measurement of the Airway Dimension by Computed Tomography Using the Full-Width-Half- Maximum Method: a Study on the Measurement Accuracy according to the CT Parameters and Size of the Airway

Abstract

Objective: To assess the influence of variable factors such as the size of the airway and the CT imaging parameters such as the reconstruction kernel, field-ofview (FOV), and slice thickness on the automatic measurement of airway dimension. Materials and Methods: An airway phantom was fabricated that contained eleven poly-acryl tubes of various lumen diameters and wall thicknesses. The measured density of the poly-acryl wall was 150 HU, and the measured density of the airspace filled with polyurethane foam was 900 HU. CT images were obtained using a 16-MDCT (multidetector CT) scanner and were reconstructed with various reconstruction kernels, thicknesses and FOV. The luminal radius and wall thickness were measured using in-house software based on the fullwidth- half-maximum method. The measured values as determined by CT and the actual dimensions of the tubes were compared. Results: Measurements were most accurate on images reconstructed with use of a standard kernel (mean error: 0.03+-0.21 mm for wall thickness and 0.12 0.11 mm for the luminal radius). There was no significant difference in accuracy among images with the use of variable slice thicknesses or a variable FOV. Below a 1-mm threshold, the measurement failed to represent the change of the real dimensions. Conclusion: Measurement accuracy was strongly influenced by the specific reconstruction kernel utilized. For accurate measurement, standardization of the imaging protocol and selection of the appropriate anatomic level are essential.