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A new method to perform quantitative measurement of bronchoscopic images

Depts of ¹ Physiology and ² Medicine, Queen's University, Kingston, Ontario, Canada

CORRESPONDENCE: P.K. McFawn, Dept of Physiology, 4th Floor Botterell Hall, Queen's University, Kingston, Ontario, K7L 3N6, Canada. Fax: 1 6135336880

Keywords: airway mechanics, bronchoscopy, endoscopy, image analysis

Received: September 6, 2000
Accepted April 18, 2001

This work was supported by the Canadian Institutes of Health Research and the Ontario Thoracic Society. P.K. McFawn was supported by the John Alexander Stewart Fellowship and a Canadian Lung Association/CIHR/GlaxoWelcome Fellowship.

Bronchoscopy is a commonly used clinical tool that provides a direct image of the bronchial lumen. However, bronchoscopy has seen little use as a quantitative measurement tool, mainly because of the wide-angle lens which distorts the image. The present authors have tested the ability of numerical algorithms and commercial software to correct for this distortion.

Test objects of known size were imaged with four different bronchoscopes. Commercial image analysis software was used to measure the size of features in the images before and after applying distortion correction algorithms. The technique was then applied by measuring airway narrowing in anaesthetized pigs during vagal stimulation.

Without correction, object size near the edge of the field of view is underestimated by 40%. The error in measured diameter of concentric circles was dependent on the radius of the circle, increasing to 25% for circles occupying 90% of the field. Third order polynomial functions were required to correct these errors. After correction, errors were independent of object size or location in the image. Correction for lens distortion was independent of the distance between bronchoscope and object.

The authors conclude that modern image processing software can correct for the distortion produced by wide-angle bronchoscope lenses.

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