A new disk method for the endoscopic determination of gastric ulcer area

0016-5107/86/3201-0020$02.00

GASTROINTESTINAL ENDOSCOPY Copyright © 1986 by the American Society for Gastrointestinal Endoscopy

A new disk method for the endoscopic determination of gastric ulcer area Haruya Okabe, MD, Masahito Ohida, MD Nobuyuki Okada, MD, Toshiharu Mitsuhashi, MD Tomoe Katsumata, MD, Katsunori Saigengi, MD Kenichi Nakahashi Kanagawa and Tokyo, Japan

The authors devised a new method using measure plates for the endoscopic measurement of gastric ulcer area. A grid composed of 2.5-mm squares was photographed by the endoscope with lens-object-distance (LOD) being changed every 2.5 mm precisely, and the obtained images of the square pattern were printed on glass plates, which were used as measure plates. The ulcer size was determined by mounting an endoscopic photograph of the ulcer on the corresponding glass plate with the same LOD, projecting them on the screen by a projector and counting the number of squares within the ulcer area. In this way the gastric ulcer size could be determined with an average aberration ratio of 5.6% or less, irrespective of LOD.

In order to evaluate the healing effect of drugs objectively, various endoscopic methods for measurement of ulcer size have been devised. However, to determine ulcer size easily and precisely was difficult. In 1980, Classen et al. l reported a newly devised method for measuring the area of an ulcer. This method uses a rubber disk placed at the center of the ulcer to be measured. The actual measurement was done by a graphic apparatus coupled with a computer. They stated that the precise area could be calculated by this method with an aberration ratio of 4.2 ± 0.5%, not considering the optical distortion of lenses. Our reexamination of this method revealed, however, that the optical distortion inherent in wide-angle endoscope lenses was too large, especially at a short distance, to make a precise determination. In order to correct the optical distortion without using special instruments, we photographed a mesh pattern of squares having sides of 2.5 mm at distances from the endoscope lens from 1 to 5 em, with intervals of 2.5 mm consecutively, and copied each picture to transparent glass plates just as in contact printing. An endoscopic photograph of an ulcer which has a rubber disk of 5 mm in diameter placed in the center is laid under the glass plate carrying the square pattern From the Department of Internal Medicine, Kitasato University, School of Medicine, Kanagawa, Japan; and Olympus Optical Co., Ltd., Tokyo, Japan. Reprint reqW!sts: Karuya Okabe, MD, Kitasato University, School of Medicine, 1-15-1, Sagamihara, 228, Japan.

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photographed at the same lens-object-distance (LOD). Then they are both enlarged by a projector. By counting the number of the squares with at least more than half within the ulcer area, it is possible to make a precise determination of the ulcer size. As the ulcer and the square pattern are equally distorted in this method, simple area determinations can be made by mounting the glass plate on the film. This method allows determination of the ulcer area more easily and more accurately. METHOD

An experimental design to measure the optical distortion rate of endoscope lenses according to Classen's method

A circle of 25 mm in diameter was drawn as a model of an ulcer. A rubber disk of 5 mm in diameter was placed in the center of the ulcer model (Fig. 1). Three types of Olympus endoscopes (GIF-P2, GIF-P3, and GTF-Bl00) were used to photograph the rubber disk in the center of the visual field at distances between the disk and the LOD from 1 to 5 em, with intervals of 2.5 mm consecutively. The LOD was measured precisely by an apparatus for optical lenses designed by Olympus Optical Co., Ltd. For the purpose of calculation of the area, the endoscopic photographs were enlarged to 100 mm in diameter in the case of GIF-P2 and GIF-P3 and to 120 mm in the vertical axis in the case of GTF-BIOO. If the image is not optically distorted by the lens, the area of the circle of 25 mm in diameter used as an ulcer model must be 25 times as large as that of the standard rubber disk GASTROINTESTINAL ENDOSCOPY

ulcer model. A set of grids must be made for each endoscope that will be used. RESULTS Area determination without accounting for optical distortion of endoscope lenses (Classen's method)

With respect to the three types of Olympus endoscopes (GIF-P2, GIF-P3, and GTF-BIOO), the area ratio and aberration ratio calculated from the ratio of the diameter of the two circles are shown in Table 1. The above results are graphically shown in Figure 2. Table 1. Relationship between lens-object-distance (LOD) and aberration ratio of gastrofiberscopes. Aberration ratio (%)

LOD

5mm 25mm Figure 1. Schema of an ulcer model.

of 5 mm in diameter. However, the outer circle will be optically more distorted due to the influence of greater optical distortion by the endoscope lens. Its influence is calculated as follows: First, the actual length (R) of the diameter of the circle of 25 mm in diameter and the actual length (r) of the rubber disk of 5 mm in diameter were measured on the enlarged photographs. Then, the ratio of the area (8) of the circle of 25 mm in diameter to the area (8') of the rubber disk 5 mm in diameter on the photograph was calculated using the formula: 8/8' = (R/2F1r/(r/2)21r = (R/R)2. The aberration ratio between the area ratio actually calculated to the theoretical area ratio was found by the formula: [(R/r)2 - 25]/25 x 100.

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VOLUME 32, NO. 1, 1986

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aberration ratio (%)

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An area determination method accounting for optical distortion of endoscope lenses

In order to account for the optical distortion of endoscope lenses for the determination of the ulcer area, we devised an area determination method using a square pattern. A grid of squares having sides of 2.5 mm was photographed by Olympus GIF-P2, GIF-P3, and GTF-B100 in the same way as the ulcer model, with the LaD changed every 2.5 mm. The photographs were enlarged on transparent celluloid plates in the same manner as the previously mentioned ulcer model method in order to make transparent area measuring plates. Then, each measuring plate was mounted on the corresponding ulcer model photograph taken at the same LaD, and the number of the squares within the circle ofthe ulcer model was counted. The number of squares with at least more than 50% of their area within the ulcer model was multiplied by 6.25 mm 2 to produce the area (8) of the

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Figure 2. Relationship between lens-object-distance (LOD) and aberration ratio of gastrofiberscopes. 21

It was found that the aberration ratio exceeds 30% when the LOD is within 2 em or 1.75 em. However, the aberration ratio becomes 10% when the LOD is 2.75 em or greater as in the case of the GTF-B100 and 4 em or larger as in the case of GIF-P2 and GIF-P3. Thus, Classen's method can be used without accounting for optical distortion when the LOD is 4 em or larger as in the case of the GIF-P2 and GIF-P3 and 3 em or larger as in the case of GTF-B100, since the area of ulcer calculated from its simple proportion to a rubber disk represents an aberration ratio under 10% in these cases. The measurement was not made in the range of an LOD smaller than 1.5 em in Table 1 and smaller than 1.25 em in Table 2, as the ulcer model did not fall within the visual field because of the small LOD distance. Area determination correcting the optical distortion

of endoscope lenses Table 2 shows the number of the distorted squares contained in the ulcer model circle and the determined area (8) at each LOD with use of the GIF-P3. The area of the ulcer model circle of 25 mm in diameter theoretically must be (25/2)211' ::; 490.6 mm 2. The aberration ratio between the determined area (8) and the theoretical figure was calculated by the formula [(8/490.6) - 1] x 100% and it is listed also. This means that if the distorted square pattern is used in order to determine the ulcer model area, a determination with an aberration ratio of about 7% or less is possible at any LOD. The average aberration is 5.60 ± 1.34%, which is Table 2. Aberration ratio of our method using the GIF-P3 endoscope.

LOD

(em)

No. of units covered with object disk

Area of object disk

83

518.75 525.00 512.50 512.50 525.00 512.50 525.00 512.50 512.50 518.75 512.50 525.00 512.50 506.25 525.00 525.00 512.50 525.00 525.00

1.25 1.50 1.75 2.00 2.25 2.50 2.75 3.00 3.25 3.50 3.75 4.00 4.25 4.50 4.75 5.00 5.25 5.50 5.75 " Mean ± SD

22

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82 82 84 82 84

82 82 83 82 84

82 81 84

84 82 84 84 =

5.60 ± 1.34.

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+5.74 +7.01 +4.46 +4.46 +7.01 +4.46 +7.01 +4.46 +4.46 +5.74 +4.46 +7.01 +4.46 +3.19 +7.01 +7.01 +4.46 +7.01 +7.01

remarkably smaller than that obtained in the previous method without correction of the optical distortion. It is also noted that at a close distance, the area determination can be made with a remarkably small aberration ratio. The same results were obtained by use of the GIF-P2 and GTF-B100 instruments. A practical method for determination of peptic ulcer area

Our experiments show that area can be determined with a small aberration irrespective of LOD by mounting the square pattern measuring plate. In order to simplify the determination process for clinical application, we copied the original endoscopic film of the square pattern on glass plates of the same size. The measuring glass plate is mounted on an endoscopic photograph of an ulcer and then projected on a screen by a projector to determine the area. Figure 3 shows the glass plate and a 16 mm photograph of an ulcer at the center. Determination of the ulcer area is made by aligning the central rubber disk on the ulcer photograph with the central two blocks (5 mm long) of the square pattern of the glass plate, and by counting the number of the squares with at least more than 50% of the square in the ulcer area. Figure 4 shows the endoscopic photograph of a gastric ulcer taken with a GTF-B100. Since 25 squares are seen within the ulcer, the ulcer area is 2.52 X 25 = 156.25 mm 2 • DISCUSSION

Various kinds of endoscopic intragastric measurement of ulcer area have been tried2 : (1) the sampling method, which includes the disk-probe and spray methods; (2) the optic method; and (3) the electrical method. In spite of the diversity of their principles, these methods are essentially the same. They all measure only the distance between two points. Each of these methods uses a combination of one-dimensional measurements as a substitute for area determination. The method of Classen et aLl was innovative and made the two-dimensional determination of ulcer area possible for the first time. Although intragastric determination using a marker of a given size was previously known, use of a thin rubber disk insertable into an endoscope establishing a marker for constant comparison in every direction was a new idea. Thus, the disk can serve as a marker theoretically independent of the extension or direction of the ulcer. Classen et a1. determined the ulcer area using a graphic apparatus coupled to a computer and stated that the aberration ratio was 4.2 ± 0.5% at any angle and distance irrespective of LOD and the angle to the object surface. However, the optical distortion of endoscope lenses was not considered by Classen et a1. GASTROINTESTINAL ENDOSCOPY

It was assumed that even a small aberration would be impossible in close distance photographing because of optical distortion of endoscope lenses. Our study on that point revealed that a precise determination is impossible in Classen's method when the LOD is under 4 cm in the case of the GIF -P2 and GIF -P3 endoscopes and under 3 cm in the case of the GTFBIOO endoscope. Accordingly we devised a method in which the optical distortion of lenses at a shorter distance can be corrected to make a precise determination and which requires no special instrument. We use a disk of 5 mm in diameter just as Classen did, but the area is determined with square pattern measuring plates. If the square pattern is optically distorted in the same way as the photograph of the ulcer, a precise area determination can be made by using the square pattern taken in the same LOD. These squares have sides of 2.5 mm and the diameter of the rubber disk marker is 5 mm. If the diameter is identical with two blocks of the square pattern, the LOD of the ulcer photograph is the same as that of the square pattern photograph, and hence their optical distortion is identical. That is, the effects of optical distortion negate each other in both photographs so that it is as good as measuring the area of a figure

Figure 4. The endoscopic picture shows a gastric ulcer taken by the GTF-B100 endoscope. The number of squares con-

tained in the ulcer is 25. The ulcer area can be calculated as (2.5)2 . 25 = 156.25 mm2. with a normal square pattern. This principle is based on the fact that the relationship between the ulcer and the square pattern remains unchanged, even if they are deformed due to the optical distortion of lenses.

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Figure 3. Some examples of the glass plate. These plates are used for the endoscopic photographs taken by the GIF-P2 endoscope to measure the ulcer area. The central film is the one which was taken by the GIF-P2 endoscope. The area is measured by mounting the glass plate on the endoscopic film. The number of the squares within the ulcer area are then counted. VOLUME 32, NO.1, 1986

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We used this method to determine the area of an ulcer model at various LODs and found that a determination can be made with an aberration ratio of 7% or less at each LOD. When the square pattern measuring plates are copied to glass plates, it is possible to determine the area by mounting the glass plate directly on the endoscopic film. Sonnenberg et al. 3 report that in an ulcer measuring test using a mannikin, 80% of the determined values were smaller than the real ones, whether or not the measurement was conducted by an expert in endoscopy or a trainee. The aberration ratio was mean ± SD = -29 ± 40% and in an extreme case the determined size was one-fourteenth of the real one. This demonstrated how large the aberration is and that no reliable results can be obtained if the determination is made based on the impression of an observer. Some points must be noted when photographing by our method. The first is the angle of the endoscope to the object surface. We photographed at various angles to determine the area, but we found it was too complicated to be applied for clinical purposes. Therefore, we decided to employ only the front view angle of 90° to the surface. We are able to confirm that the angle is 90° by the fact that the marker disk appears to be a perfect circle. Besides, since it is almost impossible to know the angle of the endoscope relative to the wall of the stomach, the photographing position of 90°

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from the stomach wall is essential for a precise area determination. Second, if the ulcer cannot be photographed in one picture because the ulcer is too large to fall within the visual field of the endoscope, a precise determination of the ulcer area is impossible. The ulcer area can be determined using our method only if the ulcer falls within the visual field of the endoscope. Third, the ulcer and the rubber disk cannot be viewed en face in some parts of the stomach, such as the anterior and posterior walls of the antrum and the posterior wall of the body, and an accurate measurement is not possible. An accurate endoscopic determination of ulcer area, which had been considered impossible, now can be made precisely and easily in a large number of cases so that the progress of healing can be observed and the healing rate of an ulcer can be plotted through a reduction curve over a period of time. This method permits a better evaluation of the effect of antiulcer drugs.

REFERENCES 1. Classen M, Dancygier H, Wurbs D. New method of endoscopic

determination of ulcer size. Gut 1980;21:895. 2. Sakita T, Oguro Y. Measurements of the lesion in size under direct vision with optical fiberscope. Gastroenterol Endosc 1973;81:456-64. 3. Sonnenberg A, Gier M, Kern L, et al. How reliable is determination of ulcer size by endoscopy? Br Med J 1979;2:1322-4.

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