Research

Quantification of the magnification and distortion effects of a pediatric flexible video-bronchoscope

IB Masters^1,3 , MM Eastburn² , PW Francis^1,3 , R Wootton⁴ , PV Zimmerman⁵ , RS Ware⁶ and AB Chang^1,3

¹  School of Medicine, Discipline of Paediatric and Child Health, University of Queensland, Herston 4029, Brisbane, Australia

²  University of Queensland, Department of Information Technology and Electrical Engineering, St Lucia 4072, Brisbane, Australia

³  Department of Respiratory Medicine, Royal Children's Hospital, Herston 4029, Brisbane, Australia

⁴  University of Queensland Centre for Online Health, Level 3 Foundation Building, Royal Children's Hospital, Herston 4029, Brisbane, Australia

⁵  Department of Thoracic Medicine, The Prince Charles Hospital, Rode Rd, Chermside 4032, Brisbane, Australia

⁶  Longitudinal Studies Unit, School of Population Health, The University of Queensland, Herston 4006, Brisbane, Australia

author email corresponding author email

Respiratory Research 2005, 6:16doi:10.1186/1465-9921-6-16

Published:	10 February 2005

Abstract

Background

Flexible video bronchoscopes, in particular the Olympus BF Type 3C160, are commonly used in pediatric respiratory medicine. There is no data on the magnification and distortion effects of these bronchoscopes yet important clinical decisions are made from the images. The aim of this study was to systematically describe the magnification and distortion of flexible bronchoscope images taken at various distances from the object.

Methods

Using images of known objects and processing these by digital video and computer programs both magnification and distortion scales were derived.

Results

Magnification changes as a linear function between 100 mm (×1) and 10 mm (×9.55) and then as an exponential function between 10 mm and 3 mm (×40) from the object. Magnification depends on the axis of orientation of the object to the optic axis or geometrical axis of the bronchoscope. Magnification also varies across the field of view with the central magnification being 39% greater than at the periphery of the field of view at 15 mm from the object. However, in the paediatric situation the diameter of the orifices is usually less than 10 mm and thus this limits the exposure to these peripheral limits of magnification reduction. Intraclass correlations for measurements and repeatability studies between instruments are very high, r = 0.96. Distortion occurs as both barrel and geometric types but both types are heterogeneous across the field of view. Distortion of geometric type ranges up to 30% at 3 mm from the object but may be as low as 5% depending on the position of the object in relation to the optic axis.

Conclusion

We conclude that the optimal working distance range is between 40 and 10 mm from the object. However the clinician should be cognisant of both variations in magnification and distortion in clinical judgements.