CALIBRATION OF ENDOSCOPIC IMAGES

In pediatric airway surgery, endoscopic evaluation of the lesions and treatment is important. However, there are no objective and reproducible methods for measurement. The purpose of this study was to define the optical effects of a Storz-Hopkins system and develop a method of calibration and measurement. Known geometric images (grids and circles) were viewed through the Storz-Hopkins system and recorded. These images were then analyzed morphometrically with a computer image analyzer (Jandel Scientific). The distortion of the endoscope could be identified, and the severity was found to be a function of the distance from the center of the field (r = .962). When this distortion factor (range, 0% to 25% shrinkage) was used mathematically, known circles could be measured by means of an endoscopic image. The error was reduced from 17.6% to 4.3% (p < .003). With morphometric programs the optical distortion of the bronchoscope can be calibrated. This can then be used to correct the measurement of images.