Korean J Radiol.  2008 Jun;9(3):226-235. 10.3348/kjr.2008.9.3.226.

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

• Kim N
• Seo JB
• Song KS
• Chae EJ
• Kang SH

• KMID: 1758456
• DOI: http://doi.org/10.3348/kjr.2008.9.3.226

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-of-view (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 full-width-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.

Keyword

Airway; Computed tomography (CT); FWHM (Full Width at Half Maximum); Measurement, phantom

MeSH Terms

Cone-Beam Computed Tomography/*methods
Feasibility Studies
Phantoms, Imaging
Respiratory System/*anatomy & histology

Figure

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  Fig. 1 Poly-acryl airway phantom and scanned CT image. A. Eleven poly-acryl artificial tubes of physical phantom with various inner diameters and wall thicknesses. Measured CT density of material was 150 HU. B. Physical phantom is filled with polyurethane foam. C. Axial CT image of phantom.

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  Fig. 2 Software design and image display. A. Schematic workflow diagram for full width at half maximum measurement approach. B. Image overlay of measured results on CT images of physical airway phantom (airway wall, dark gray; lumen, gray; average wall in case of wall outside 2SD, bright gray).

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  Fig. 3 Effect of reconstruction kernel on accuracy of airway wall measurement. Estimated wall thickness as compared with actual wall thickness (Reference) were determined with use of every reconstruction kernel. All images were reconstructed with 0.75-mm slice thickness and 360-mm field of view parameters.

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  Fig. 4 Effect of field of view on accuracy of airway wall measurement. All images were reconstructed with use of standard kernel (B50f) and 0.75 mm slice thickness. Measured airway wall thicknesses on CT image with various field of views are not significantly different from actual wall thicknesses. Even with use of smaller field of view, measurement accuracy of wall thicknesses less than 1 mm was not improved.

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  Fig. 5 Effect of slice thickness on accuracy of airway wall measurement. All images were reconstructed with use of standard kernel (B50f) and 0.75 mm slice thickness. Measured airway wall thicknesses determined with various reconstructed slice thicknesses were not significantly different from actual wall thicknesses.

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  Fig. 6 Difference between actual and estimated airway luminal radius against actual airway luminal radius with use of various reconstructed kernels (B30f, B50f, and B70f). All images were reconstructed with 0.75-mm slice thickness and 360-mm field of view parameters.

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