GB2347521A

GB2347521A - Medical endoscope with angularly adjustable interference filter

Info

Publication number: GB2347521A
Application number: GB0001443A
Authority: GB
Inventors: Mathias Kraas; Andreas Mueckner
Original assignee: Olympus Winter and Ibe GmbH
Current assignee: Olympus Winter and Ibe GmbH
Priority date: 1999-01-21
Filing date: 2000-01-21
Publication date: 2000-09-06
Also published as: FR2788681B1; FR2788681A1; DE19902184C1; JP2000210247A; GB0001443D0

Abstract

An endoscope with an illumination device 1, 8 that includes a short-pass filter 11 and which also has a viewing device 2, 4, 3 with a long-pass filter 5 for viewing red fluorescence excited by the illumination device. One of these two filters is an interference filter that is angularly adjustable so that the transmission wavelength of the transmitted illumination light is below the wavelength range of the transmitted fluorescent light.

Description

2347521 MEDICAL ENDOSCOPE The invention relates to an endoscope of the

type including an illumination device which includes a short-pass filter, for illuminating a region to be viewed, at least a portion of which region may be caused to fluoresce in the red region by the impingement of the radiation from the illumination device, and a viewing device, which includes a long-pass filter.' one of the two filters being constructed in the form of AnInterference filter, the transmission lines of the two filters representing the intensity of the transmitted light against its wavelength, intersecting at a wavelength below the wavelength range of the fluorescent radiation.

Fluorescence effects are helpful in the endoscopic examination of regions of the body, for instance the bladder wall. Bodily tissue contains, amongst other things, small proportions of fluorescent substances which are irradiated and stimulated by the illumination device of the endoscope. Since different types of tissue fluoresce with different intensities, differences in tissue may be differentiated and e.g. tumours detected. The fluorescence effect is, however, very weak with this autofluorescence of fluorescent substances normally present in tissue and may be scarcely detected against the strong irradiation light. Stronger fluorescence effects may be achieved by staining with fluorescent materials. A proven method treats the tissue with substances which are converted into fluorescent substances in the tissue to be detected, that is to say e.g. the tumour tissue. -Strong, easily visible fluorescence effects may thus be achieved.

2 With all such examinations which make use of fluorescence, there are, however, problems with the very much stronger light of the illumination device swamping the fluorescent light. With suitable narrow-band filters in the viewing device it is possible to make only the fluorescent light visible and suppress the light from the illumination device. However, one then sees only the fluorescent light; non-fluorescent regions are invisible so that orientation and location of the fluorescent regions is difficult.

The best solution is to make both the fluorescent and the non-fluorescent regions visible, but in different colours, to enable them to be easily differentiated.

An endoscope of the type referred to above, is disclosed in DE 19639653 Al.

The transmission lines of the filters of such endoscopes intersect at a shorter wavelength than that of the fluorescent light. Light from the illumination device is permitted through in a narrow band in the region in which the transmission spectra of the filters overlap with a wavelength which differs from that of the fluorescent light. When viewing the fluorescent marked region, the viewer thus sees e.g. blue background light and red fluorescent light. The background light is in a narrow band and relatively faint with a suitable overlap of the transmission spectra so that the fluorescent marked regions are easily visible against the background, which is also visible and may be used for orientation purposes.

In the aforementioned known construction, the filters are provided with fixed transmission lines which are, however, subject to manufacturing tolerances.

The background light which is let through is thus subject to variance in its

I 3 intensity. Depending on the circumstances, there tends to be either too much background light, which makes the detection of the fluorescent light more difficult, or too little background light, which makes correlation with the background difficult.

A fluorescence microscope, which is not of the type referred to above, is disclosed in US 5371624 in which a band pass interference filter is arranged to be angularly adjustable with respect to the direction of the light in order to displace the transmission spectrum with respect to the fluorescence lines to be to viewed.

It is the object of the present invention to improve an endoscope of the type referred to above as regards the balanced relationship of background light and fluorescent light.

According to the present invention the interference filter is mounted to be angularly adjustable with respect to the direction of the beam path of the light which passes through it.

In accordance with the, invention, one of the filters, which is in the form of an interference filter, is arranged to be angularly adjustable. The position of its transmission line may thus be displaced. The intersection point of the two transmission lines may thus be moved. It can be moved to higher or lower transmission intensities at the intersection point. The background light let 25 through in the overlapping region of the transmission spectra of the two filters is correspondingly increased or attenuated. When setting up the endoscope, an optimum balance with the intensity of the fluorescent light can thus be made.

4 An adjustment can optionally also be effected by action of the user during an examination in order e.g. to make the background lighter for the purpose of better orientation during an initial survey viewing and subsequently making the background darker in order to be able to view fluorescent regions very precisely. The endoscope in accordance wtih the invention is also particularly suitable for viewing autofluorescence since the background light can be strongly attenuated in order to be able to view weak autofluorescence effects.

The adjustability of the intensity of the background light also permits further problems to be solved, e.g. those caused by the differing colour sensitivity of the human eye and a video camera. Thus the background light can be adjusted to the same intensity as the fluorescent light, e.g. when viewing with the eye which has e.g. the same sensitivity to blue background light and red fluorescent light. The background light can be increased with a CCD camera, which has a lower blue sensitivity, and reduced with a Vidicon camera, which has a lower red sensitivity. - The interference filter may be arranged in the illumination device which preferably comprises a light source which is connected to a light guide cable and in which the interference filter is disposed. An interference filter, which absorbs little, is to be preferred for thermal reasons in the illumination device, in which there is a high light intensity. The arrangement of the interference filter in the light source is also advantageous for space reasons since there are better possibilities for arranging a suitable pivotal mechanism there.

Further details of the invention will be apparent from the following description of one specific embodiment which is given by way of example with reference to the accompanying drawings, in which:

I Figure I is a highly schematic view of an endoscope in accordance with the invention; and Figure 2 is a diagrammatic view of the filter transmission curves in which the light intensity (T) is plotted against wavelength (k). As shown in Figure 1, the endoscope includes an elongate housing 1, provided at whose distal end there is an objective 2 and at whose proximal end there is an 10 ocular 3. The image is transmitted between them by an image guide 4, for instance a rod lens arrangement or a fibre light guide arrangement. Also provided at a suitable point in the image path is a long-pass filter 5 which is e.g. constructed conventionally in the form of a coloured glass filter. 15 The region 6 to be viewed, for instance a section of the wall of a human bladder, into the vicinity of which the thin, elongate housing I of the housing is introduced, is illuminated by means of a light guide constituted by a fibre bundle 7. The light guide fibre bundle extends within the housing 1, passes through its wall and extends externally to a broad band light source 8 in which a 20 lamp 9 illuminates its end, in the illustrated exemplary embodiment via a condensor device with lenses -1-0., Arranged between the lenses 10 in the exemplary embodiment is a short-pass filter 11, which is constructed in the form of an interference filter. This is, for 25 instance, a glass plate which is provided with an optical thin layer arrangement such that light below a predetermined wavelength is permitted through but above it is not permitted through, the transition or cut off being as steep as 6 possible.

As may be seen in Figure 1, the short pass filter I I is mounted so as to be pivotable about a shaft 12 in the direction of the arrow and its angular position with respect to the light passing through it can be adjusted with an adjusting device, which is not shown, for instance by means of a rotary knob disposed externally on the housing of the light source 8.

The transmission curves, i.e. the plots of the intensity of the transmitted radiation against wavelength of the two filters are shown in Figure 2, marked with the reference numerals of the filters 5 and 11, as in Figure 1. It will be seen that the short-pass filter transmits below the wavelength range designated "blue" but cuts off above it. Conversely, the transmission curve of the longpass filter 5 provided in the viewing device 2, 4, 3 lets light through only above this wavelength range. The curves 5 and I I intersect at an intersection point 13. Light from the broad band light source 8 is thus permitted to reach the occular 3 only in the blue wavelength region within the chain line 14. Of the broad band light produced by the lamp 9, the viewer thus sees only that proportion lying within the line 14 as a result of the two filters 5 and 11. 20 The short-wave light transmitted through the short- pass filter I I onto the region 6 stimulates fluorescence there at fluorescent marked regions which produces fluorescence radiation within the chain line 15, in the long wavelength red range. The fluorescence line 15 and the background line 14 may thus be clearly 25 distinguished by their colour.

The gradient of the transmission lines of the filters 5 and I I and the position of I 7 the intersection point 13 are critical for the height and breadth of the background line 14. The transmission lines of the two filters can be subject to manufacturing deviations. The transmission at the intersection point 13 can thus be higher or lower than shown in Figure 2. A stronger or weaker background line is the result. The background radiation should desirably, however, as shown, be as closely as possible of the same intensity as the fluorescence radiation in order not to swamp it.

If the angular position of the short-pass filter constructed in the form of an interference filter, with respect to the direction of the light path is altered by rotation about the shaft 12, the edge of the transmission curve I I moves, as is shown by the chain lines in Figure 2. The intersection point 13 can thus be moved to higher or lower transmission intensities and the background line 14 can be accentuated or attenuated. A desired intensity relationship between the lines 14 and 15 can thus be set by suitable angular adjustment of the short-pass filter 11.

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Claims

1. A medical endoscope including an illumination device which includes a short-pass filter, for illuminating a region to be viewed, at least a portion of which region may be caused to fluoresce in the red region by the impingement of the radiation from the illumination device, and a viewing device, which includes a long-pass filter, one of the two filters being constructed in the form of an interference filter, the transmission lines of the two filters representing the intensity of the transmitted light against its wavelength, intersecting at a wavelength below the wavelength range of the fluorescent radiation, the interference filter being mounted to be angularly adjustable with respect to the direction of the beam path of the light which passes through it.

2. An endoscope as claimed in Claim 1, in which the interference filter is arranged in the illumination device.

3. An endoscope as claimed in Claim 2, in which the illumination device comprises a light source, which is connected to a light guide cable and in which the interference filter is disposed.

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