Abstract
BackgroundFlexible 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.MethodsUsing images of known objects and processing these by digital video and computer programs both magnification and distortion scales were derived.ResultsMagnification 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.ConclusionWe 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.
Highlights
The flexible bronchoscope has been used in pediatrics for more than 20 years [1] yet there are only a limited number of publications on the systematic examination of the physical properties of magnification and distortion found in endoscopes of any size, let alone bronchoscopes specific for the pediatric sized airways. [1,2,3,4,5,6]
They use charge coupled devices (CCD's) which are mounted adjacent to the lens essentially converting the image to electrical energy at the lens. This early conversion of the image has the effect of producing "less noise" allowing greater image clarity. All of these issues mentioned are important to the clinical use of flexible videobronchoscope (FVB's) and subsequent patient management and as the Olympus company was unable to provide the necessary details on magnification and distortion, we undertook to quantify these effects in order to enhance our decision making quality during FVB procedures
The mean linear magnification for the bronchoscopes aligned along the central geometrical axis of the bronchoscope over the range of the depth of field from 100 mm to
Summary
The flexible bronchoscope has been used in pediatrics for more than 20 years [1] yet there are only a limited number of publications on the systematic examination of the physical properties of magnification and distortion found in endoscopes of any size, let alone bronchoscopes specific for the pediatric sized airways. [1,2,3,4,5,6]. Curvilinear distortion is described where straight lines are rendered as curved either inward (pincushion) or outwards (barrel) curves This form of distortion is a result of asymmetry of lens configuration and is a feature of bronchoscopes and most endoscopes in general[2,5,16]. The more recently developed bronchoscopes such as the flexible videobronchoscope (FVB's) have moved away from fibreoptics to transmit images They use charge coupled devices (CCD's) which are mounted adjacent to the lens essentially converting the image to electrical energy at the lens. This early conversion of the image has the effect of producing "less noise" allowing greater image clarity. The aim of this study was to systematically describe the magnification and distortion of flexible bronchoscope images taken at various distances from the object
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