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Proceedings Paper

Automatic measurement of oblique-oriented airway dimension at volumetric CT: effect of imaging parameters and obliquity of airway with FWHM method using a physical phantom
Author(s): Namkug Kim; Joon Beom Seo; Koun Sik Song M.D.; Suk-Ho Kang
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Paper Abstract

This study is conducted to assess the influence of various CT imaging parameters and airway obliquity, such as reconstruction kernel, field of view, slice thickness, and obliquity of airway on automatic measurement of airway wall thickness with FWHM method and physical phantom. The phantom, consists of 11 poly-acryl tubes with various inner lumen diameters and thickness, was used in this study. The measured density of the wall was 150HU. The airspace outside of tube was filled with poly-urethane foam, whose density was -900HU, which is similar density of emphysema region. CT images, obtained with MDCT (Sensation 16, Siemens), was reconstructed with various reconstruction kernel (B10f, B30f, B50f, B70f and B80f), different field of views (180mm, 270mm, 360mm), and different thicknesses (0.75, 1, and 2 mm). The phantom was scanned at various oblique angles (0, 30, 45, 60 degree). Using in-house airway measurement software, central axis of oblique airway was determined by 3D thinning algorithm and CT image perpendicular to the axis was reconstructed. The luminal area, outer boundary, and wall thickness was measured by FWHM method at each image. Actual dimension of each tube and measured CT values on each CT data set was compared. Sharper reconstruction kernel, thicker image thickness, and larger oblique angle of airway axis results in decrease of measured wall thickness. There was internal interaction between imaging parameters and obliquity of airway on the accuracy of measurement. There was a threshold point of 1-mm wall thickness, below which the measurement failed to represent the change of real thickness. Even using the smaller FOV, the accuracy was not improved. Usage of standard kernel (B50f) and 0.75mm thickness results in the most accurate measurement results, which is independent of obliquity of airway. (Mean error: 0 Degree 0.067±0.05mm, 30 Degree 0.076±0.09, 45 Degree 0.074±0.09, 60 Degree 0.091±0.09). In this imaging parameters, there was no significant difference (paired t-test : p > 0.05) between actual measurement and each oblique angle measurement. The accuracy of airway wall measurement was strongly influenced by imaging parameters and obliquity of airway. For the accurate measurement, independent of obliquity, we recommend the CT images reconstructed with 0.75mm slice thickness and B50f or B30f with sharpening filter.

Paper Details

Date Published: 26 March 2007
PDF: 11 pages
Proc. SPIE 6512, Medical Imaging 2007: Image Processing, 65123C (26 March 2007); doi: 10.1117/12.710291
Show Author Affiliations
Namkug Kim, Univ. of Ulsan College of Medicine, Asan Medical Ctr. (South Korea)
Seoul National Univ. (South Korea)
Joon Beom Seo, Univ. of Ulsan College of Medicine, Asan Medical Ctr. (South Korea)
Koun Sik Song M.D., Univ. of Ulsan College of Medicine, Asan Medical Ctr. (South Korea)
Suk-Ho Kang, Seoul National Univ. (South Korea)

Published in SPIE Proceedings Vol. 6512:
Medical Imaging 2007: Image Processing
Josien P. W. Pluim; Joseph M. Reinhardt, Editor(s)

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