Proceedings Article | 26 March 2007
KEYWORDS: Computed tomography, Error analysis, Foam, Emphysema, Reconstruction algorithms, Lung, Radiology, 3D image processing, 3D metrology, Image filtering
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.
