GB2301680A

GB2301680A - Endoscope having optical means to judge object distance

Info

Publication number: GB2301680A
Application number: GB9511240A
Authority: GB
Inventors: Leslie Charles Laycock
Original assignee: GEC Marconi Ltd; Marconi Co Ltd
Current assignee: BAE Systems Electronics Ltd
Priority date: 1995-06-03
Filing date: 1995-06-03
Publication date: 1996-12-11
Anticipated expiration: 2015-06-03
Also published as: GB2301680B; GB9511240D0

Abstract

An endoscope comprises an optical system for forming an image of e.g. organs inside a patient's body, and a relay system e.g. optical fibres, for relaying the image. Endoscopes provide a two-dimensional image only and so do not provide information on the size and distance of objects in the field of view of the endoscope. The invention includes means for projecting a reference region, e.g. optic fibre 8, lenses 9, 12 and hologram 11, onto an object 15 and means for obtaining a measure of the distance of the object as well as its size based on the size of the reference region imaged in the optical system.

Description

AN ENDOSCOPE This invention relates to endoscopes.

Endoscopes are devices which can be used in medicine for inspecting the internal organs of a patient e.g. for diagnosis or during surgery. Typically, such endoscopes comprise an optical system, usually a lens or lenses, for forming an image of an object and a relay system for relaying this image e.g. to a television monitor for viewing by a surgeon.

Endoscopes which are rigid have been used in neurosurgery, and these usually relay the image by a series of lenses. Endoscopes can also be flexible for ease of manipulation inside the body, and in which case the image is normally relayed by optical fibres.

One of the problems which are encountered in such endoscopes is that the image that they generate is only two-dimensional. When using such endoscopes, a surgeon lacks information concerning the size of objects in the field of view of the endoscope and the distance of these objects from the endoscope. Such information is useful when the surgeon is performing, for example, minimal invasive surgery.

To alleviate this problem, a three-dimensional image display system has been proposed.

Two television cameras are used which receive slightly different images of the field of view via respective laterally spaced apart fibre bundles. The signals from the cameras are used to generate two images which are polarised in different planes so that they can be displayed together, to enable a user to view a three dimensional image using spectacles where each lens transmits the appropriate polarisation. However, such a system adds to the volume of the apparatus, and requires special viewing conditions.

The invention provides an endoscope comprising an optical system for forming an image of an object, means for projecting a reference region onto the object and means for obtaining a measure of the distance of the object based on the size of the reference region imaged in the optical system.

Possible means for projecting a reference region onto an object comprises an optical fibre which transmits laser light through a hologram of e.g. an annulus to form an annular beam which may be collimated or converging.

An endoscope constructed in accordance with the invention will now be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a schematic diagram of the endoscope, with suitable illumination and image processing means; and Figure 2 is a ray diagram of projection means of the optical system of the endoscope of Figure 1.

Referring to Figure 1. the endoscope comprises an optical system, indicated generally by the reference numeral 1, which is able to form an image of objects in its field of view and an optical relay system in the form of a fibre optic cable 2. The fibre optic cable 2 consists of a coherent fibre bundle, that is to say, the optical fibres are carefully arranged so that their terminations occupy the same relative positions at both ends of the fibre optic cable. The fibre optic cable 2 relays the image as formed by the optical system 1 to an image processing arrangement which comprises a lens 3, a video camera 4 and a television monitor 5. The image formed by the lens 3 is conveyed by video camera 4 to the television monitor 5 to enable e.g. a surgeon to see the field of view of the endoscope.There is also provided a second fibre optic cable 6, which has terminations close to the optical system 1 and conveys light from a source 7 in order that the field of view of the endoscope is illuminated when in use e.g. inside a human body.

Referring to Figure 2 there is provided means for projecting a reference region onto the object to be viewed. The means for projecting a reference region comprises an optical fibre 8 having a lens 9 at its termination, which transmits a collimated beam of laser light 10 from a source (not shown) located at the other termination of the fibre, independently of the fibre optic cable 6 and light source 7 of Figure 1, and a holographic element 11.

The holographic element 11 is positioned at the back focal plane of a lens 12 and is aligned so that the collimated laser beam 10 illuminates it perpendicularly to its surface.

The holographic element 11 is held in place by a layer of transparent material 13. The holographic element 11 is such as to project an image of known dimensions e.g. an annulus 14 onto the object 15. The collimated laser light beam 10 is transmitted through the holographic element 11, passes through the lens 12 and forms a collimated annular beam 16. This projects an annulus 14 onto the object 15 e.g. an organ of the body and, because the dimensions of the annulus are known, this acts as a reference by which the sizes of objects of interest in the field of view of the endoscope may be ascertained. In addition. the size of the annulus 17 as imaged by the lens 12 onto the end of the fibre optic bundle 2 gives a measure of the distance of the object 15 from the end of the fibre optic bundle.Thus, lens 12 images the object 15 onto the end of the fibre optic bundle 2 as shown by the light rays 18. If the object 15 is far from the end of the fibre optic bundle 2, the actual size of the annulus image 17 on the bundle will be small. For example, it may only occupy a few pixels. Alternatively, if the object 15 is near to the end of the fibre optic bundle 2, the actual size of the annulus image 17 on the bundle will be larger. More pixels will be illuminated by the annulus. In this way, the operator obtains an indication of the distance of the object 15 from the tip of the endoscope.

A suitable laser for illuminating the holographic element is a He/Ne type, transmitting at 544nm. This would project a green reference symbol which provides a suitable contrast with the objects in the endoscope's field of view.

If the position of the holographic element 11 is changed such that it lies between the back focal place of the lens 12 and the fibre optic bundle 2, the annular beam will converge as it propagates from the endoscope. Thus, at a given distance the annulus will appear to be smaller than in the case where the annulus is formed by the collimated annular beam. In addition, as the distance between the object 15 and the lens 12 increases beyond the focal length of the lens, the annulus will undergo a Fourier Transform and will tend to revert to the pattern of the holographic element, in this case a zero-order Bessel distribution. Both of these effects may be utilised to provide information on the size and distance of objects in the endoscope's field of view.Clearly, image processing means would need to be provided to relate the actual size and shape of the annulus imaged onto the endoscope tip to the distance of the object from the endoscope tip.

Variations may be made without departing from the scope of the invention. For instance, the optical fibre 8 need not be situated at the centre of the fibre optic bundle 2, for example it may be positioned at the periphery of the bundle. In this case the illuminating beam can be allowed to overspill the hologram 11 without interfering with the imaging system of the endoscope. Hence a diverging beam can be used i.e. a collimating lens on the end of the illumination fibre may not be required. In the embodiment of Figure 2, the annulus has been shown as being projected by means of a laser and a holographic element. The invention is not limited to the generation of the reference region in this way.Thus, for example the holographic element 11 could be replaced by a photographic mask, e.g. a glass slide, in which case the illuminating optical fibre 8 would be positioned at the centre of the fibre optic bundle 2.

The laser need not emit visible light, for example a near infra-red solid state laser may form a reference region. The fact that it is not visible may be an advantage. Processing means would be used to provide an alternate indication of depth - for example, text could be displayed stating the distance of the object.

The expansion and compression of the field of view by means of the lenses 3 and 8 described in our copending patent application number P/60596/MRC may be employed.

With regard to the reference region, this is not restricted to an annul us e.g. a grid or a Bessel beam could be employed. A Bessel beam projects a pattern having a sharp non-diverging central maximum surrounded by equispaced rings and corresponds to a zero-order Bessel function.

The endoscopes of the invention may be adapted for use in the abdominal areas (these sometimes being referred to as laparoscopes). Further, the endoscopes of the invention are not restricted to medical applications, for instance, in industry such endoscopes could be used for inspection and photography of remotely situated parts of machinery and equipment.

Claims

1. An endoscope comprising an optical system for forming an image of an object, means for projecting a reference region onto the object and means for obtaining a measure of the distance of the object based on the size of the reference region imaged in the optical system.

2. An endoscope as claimed in claim 1 in which the means for projecting a reference region comprises reconstruction of a holographic image by illumination of a hologram.

3. An endoscope as claimed in claim 1, in which the means for projecting a reference region comprises reconstruction of a photographic image by illumination of a photographic mask.

4. An endoscope as claimed in claim 2 or claim 3, in which the illumination is transmitted by optical fibre.

5. An endoscope as claimed in claim 4, in which the optical fibre is situated at the centre of a fibre optic bundle.

6. An endoscope as claimed in claim 4 as appended to claim 2. in which the optical fibre is situated at the periphery of a fibre optic bundle.

An An endoscope as claimed in any one of claims 2 to 6. in which the illumination is provided by laser.

8. An endoscope as claimed in any one of claims 1 to 7, in which the reference region is projected by a collimated beam.

9. An endoscope as claimed in any one of claims 1 to 7 in which the reference region is projected by a converging beam.

10. An endoscope as claimed in claims 1 to 9 in which the reference region is not formed by visible radiation.

11. An endoscope substantially as hereinbefore described with reference to Figures 1 and 2 of the accompanying drawings.

12. Apparatus including an endoscope as claimed in any one of claims 1 to 11.