Clin Endosc.  2012 Sep;45(3):182-188.

Feasibility of Obtaining Quantitative 3-Dimensional Information Using Conventional Endoscope: A Pilot Study

• Hyun JJ
• Chun HJ
• Keum B
• Seo YS
• Kim YS
• Jeen YT
• Lee HS
• Um SH
• Kim CD
• Ryu HS
• Lim JW
• Woo DG
• Kim YJ
• Lim MT

Abstract

BACKGROUND/AIMS
Three-dimensional (3D) imaging is gaining popularity and has been partly adopted in laparoscopic surgery or robotic surgery but has not been applied to gastrointestinal endoscopy. As a first step, we conducted an experiment to evaluate whether images obtained by conventional gastrointestinal endoscopy could be used to acquire quantitative 3D information.
METHODS
Two endoscopes (GIF-H260) were used in a Borrmann type I tumor model made of clay. The endoscopes were calibrated by correcting the barrel distortion and perspective distortion. Obtained images were converted to gray-level image, and the characteristics of the images were obtained by edge detection. Finally, data on 3D parameters were measured by using epipolar geometry, two view geometry, and pinhole camera model.
RESULTS
The focal length (f) of endoscope at 30 mm was 258.49 pixels. Two endoscopes were fixed at predetermined distance, 12 mm (d12). After matching and calculating disparity (v2-v1), which was 106 pixels, the calculated length between the camera and object (L) was 29.26 mm. The height of the object projected onto the image (h) was then applied to the pinhole camera model, and the result of H (height and width) was 38.21 mm and 41.72 mm, respectively. Measurements were conducted from 2 different locations. The measurement errors ranged from 2.98% to 7.00% with the current Borrmann type I tumor model.
CONCLUSIONS
It was feasible to obtain parameters necessary for 3D analysis and to apply the data to epipolar geometry with conventional gastrointestinal endoscope to calculate the size of an object.

Keyword

3-dimensional imaging; Endoscopes; Distortion; Epipolar geometry

MeSH Terms

Aluminum Silicates
Endoscopes
Endoscopes, Gastrointestinal
Endoscopy, Gastrointestinal
Laparoscopy
Pilot Projects
Resin Cements
Aluminum Silicates
Resin Cements

Figure

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  Fig. 1 An example of distorted image by an endoscope. Fish-eye lens utilized in endoscope causes barrel distortion of the original image (A), rendering distorted images (B, C, D).

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  Fig. 2 Correction of barrel distortion and perspective distortion. To be able to use images obtained by endoscopes for further analysis, the original image should be preprocessed by correcting the barrel distortion and perspective distortion.

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  Fig. 3 An example of stereo-images. Stereo-image is a pair of images captured by two cameras. Matching is the process of finding the corresponding position of the point on the left image with that of the right image. Disparity is relative position of a point in an image.

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  Fig. 4 Epipolar geometry. When the points connecting M, M1, M2, etc. are observed from CL, it is observed as a dot on its image plane as mL, but when these points are observed from CR, it is observed as a line on its image plane as eR-mR.

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  Fig. 5 Two view geometry of cameras. In this model, d12 is the distance between two cameras, f the focal length, L the distance between the cameras and the object, and v1-v2 the disparity.

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  Fig. 6 Pinhole camera model. In this model, f is the focal length, C the camera centre, c the image centre, h the image point of H, and L the distance between the camera center and the object.

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  Fig. 7 The stereo-image of Borrmann type I tumor model. The matching point was (left, 374, 241) and (right, 265, 231), and the resulting disparity was 106 pixels.

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  Fig. 8 The stereo-image of preliminary Borrmann type I tumor experimental model. When two endoscopes of the same model and equal illuminating power were used simultaneously to obtain stereo-images, light interference occurred, leaving behind artifacts resembling a comet's tails.

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