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Semi-automatic measurement of the airway dimension by computed tomography using the full-with-half-maximum method: a study of the measurement accuracy according to the orientation of an artificial airway.

Kim N, Seo JB, Song KS, Chae EJ, Kang SH - Korean J Radiol (2008 May-Jun)

Bottom Line: A sharper reconstruction kernel, thicker image thickness and larger tilt angle of the airway axis resulted in a significant decrease of the measured wall thickness and an increase of the measured luminal radius.Use of a standard kernel and a 0.75-mm slice thickness resulted in the most accurate measurement of airway dimension, which was independent of obliquity.For the accurate measurement of airway thickness, the CT images should be reconstructed with a standard kernel and a 0.75 mm slice thickness.

View Article: PubMed Central - PubMed

Affiliation: Department of Radiology and Research Institute of Radiology, University of Ulsan College of Medicine, Asan Medical Center, Seoul, Korea.

ABSTRACT

Objective: To develop an algorithm to measure the dimensions of an airway oriented obliquely on a volumetric CT, as well as assess the effect of the imaging parameters on the correct measurement of the airway dimension.

Materials and methods: An airway phantom with 11 poly-acryl tubes of various lumen diameters and wall thicknesses was scanned using a 16-MDCT (multidetector CT) at various tilt angles (0, 30, 45, and 60 degrees ). The CT images were reconstructed at various reconstruction kernels and thicknesses. The axis of each airway was determined using the 3D thinning algorithm, with images perpendicular to the axis being reconstructed. The luminal radius and wall thickness was measured by the full-width-half-maximum method. The influence of the CT parameters (the size of the airways, obliquity on the radius and wall thickness) was assessed by comparing the actual dimension of each tube with the estimated values.

Results: The 3D thinning algorithm correctly determined the axis of the oblique airway in all tubes (mean error: 0.91 +/- 0.82 degrees ). A sharper reconstruction kernel, thicker image thickness and larger tilt angle of the airway axis resulted in a significant decrease of the measured wall thickness and an increase of the measured luminal radius. Use of a standard kernel and a 0.75-mm slice thickness resulted in the most accurate measurement of airway dimension, which was independent of obliquity.

Conclusion: The airway obliquity and imaging parameters have a strong influence on the accuracy of the airway wall measurement. For the accurate measurement of airway thickness, the CT images should be reconstructed with a standard kernel and a 0.75 mm slice thickness.

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Related in: MedlinePlus

Effect of tilt angle and its influence on accuracy of airway wall measurement. All images were reconstructed with 0.75-mm slice thickness, standard reconstruction kernel (B50f), and 360-mm field of view. No significant difference in accuracy of airway wall measurements was observed at four different tilt angles. Airway thicknesses are overestimated for all images if airway thickness is smaller than 1 mm.
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Figure 3: Effect of tilt angle and its influence on accuracy of airway wall measurement. All images were reconstructed with 0.75-mm slice thickness, standard reconstruction kernel (B50f), and 360-mm field of view. No significant difference in accuracy of airway wall measurements was observed at four different tilt angles. Airway thicknesses are overestimated for all images if airway thickness is smaller than 1 mm.

Mentions: Figure 3 shows the actual and estimated wall thicknesses of the airway at the four measured tilt angles. We found no statistically significant difference among the four tilt angles with 0.75 mm slice thickness, a standard reconstruction kernel (B50f), and an FOV of 360 mm, although general increases in measurement error increased as the tilt angle increased from 0° to 60° (Table 2). If the wall thickness of the airway is less than 1 mm and therefore be within the magnitude of a single pixel, a rapidly increasing amount of errors was observed in the airway wall measurement. The small airway with less than a 1-mm wall thickness (1st and 2nd airways) were excluded in all of the statistical tests performed to determine the degree of error.


Semi-automatic measurement of the airway dimension by computed tomography using the full-with-half-maximum method: a study of the measurement accuracy according to the orientation of an artificial airway.

Kim N, Seo JB, Song KS, Chae EJ, Kang SH - Korean J Radiol (2008 May-Jun)

Effect of tilt angle and its influence on accuracy of airway wall measurement. All images were reconstructed with 0.75-mm slice thickness, standard reconstruction kernel (B50f), and 360-mm field of view. No significant difference in accuracy of airway wall measurements was observed at four different tilt angles. Airway thicknesses are overestimated for all images if airway thickness is smaller than 1 mm.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC2627256&req=5

Figure 3: Effect of tilt angle and its influence on accuracy of airway wall measurement. All images were reconstructed with 0.75-mm slice thickness, standard reconstruction kernel (B50f), and 360-mm field of view. No significant difference in accuracy of airway wall measurements was observed at four different tilt angles. Airway thicknesses are overestimated for all images if airway thickness is smaller than 1 mm.
Mentions: Figure 3 shows the actual and estimated wall thicknesses of the airway at the four measured tilt angles. We found no statistically significant difference among the four tilt angles with 0.75 mm slice thickness, a standard reconstruction kernel (B50f), and an FOV of 360 mm, although general increases in measurement error increased as the tilt angle increased from 0° to 60° (Table 2). If the wall thickness of the airway is less than 1 mm and therefore be within the magnitude of a single pixel, a rapidly increasing amount of errors was observed in the airway wall measurement. The small airway with less than a 1-mm wall thickness (1st and 2nd airways) were excluded in all of the statistical tests performed to determine the degree of error.

Bottom Line: A sharper reconstruction kernel, thicker image thickness and larger tilt angle of the airway axis resulted in a significant decrease of the measured wall thickness and an increase of the measured luminal radius.Use of a standard kernel and a 0.75-mm slice thickness resulted in the most accurate measurement of airway dimension, which was independent of obliquity.For the accurate measurement of airway thickness, the CT images should be reconstructed with a standard kernel and a 0.75 mm slice thickness.

View Article: PubMed Central - PubMed

Affiliation: Department of Radiology and Research Institute of Radiology, University of Ulsan College of Medicine, Asan Medical Center, Seoul, Korea.

ABSTRACT

Objective: To develop an algorithm to measure the dimensions of an airway oriented obliquely on a volumetric CT, as well as assess the effect of the imaging parameters on the correct measurement of the airway dimension.

Materials and methods: An airway phantom with 11 poly-acryl tubes of various lumen diameters and wall thicknesses was scanned using a 16-MDCT (multidetector CT) at various tilt angles (0, 30, 45, and 60 degrees ). The CT images were reconstructed at various reconstruction kernels and thicknesses. The axis of each airway was determined using the 3D thinning algorithm, with images perpendicular to the axis being reconstructed. The luminal radius and wall thickness was measured by the full-width-half-maximum method. The influence of the CT parameters (the size of the airways, obliquity on the radius and wall thickness) was assessed by comparing the actual dimension of each tube with the estimated values.

Results: The 3D thinning algorithm correctly determined the axis of the oblique airway in all tubes (mean error: 0.91 +/- 0.82 degrees ). A sharper reconstruction kernel, thicker image thickness and larger tilt angle of the airway axis resulted in a significant decrease of the measured wall thickness and an increase of the measured luminal radius. Use of a standard kernel and a 0.75-mm slice thickness resulted in the most accurate measurement of airway dimension, which was independent of obliquity.

Conclusion: The airway obliquity and imaging parameters have a strong influence on the accuracy of the airway wall measurement. For the accurate measurement of airway thickness, the CT images should be reconstructed with a standard kernel and a 0.75 mm slice thickness.

Show MeSH
Related in: MedlinePlus