Endoscopes

Have you ever wondered how TV crews get those amazing shots of the insides of our bodies in action? It is a technique that is now in widespread use by physicians, allowing them to inspect our organs with little or no surgery required. The endoscope is a system that allows the viewing of an object through a long tube.

Such systems include rigid and flexible endoscopes. The rigid endoscopes use a series of lenses to project an image from deep inside the body to a position where it may be viewed by eye or by a camera. Such a system is shown below, and comes from the Storz web site.

What sort of design considerations are needed? We need to get as many rays as possible that leave the object back to where they can be viewed by the operator as a bright image. So a detailed consideration of which rays get through the sytem is important. We may wish to see a wide range of angles out the end of the endoscope, so a consideration of the field of view and magnification of the endoscope is needed. And we wish to have a clear colour image, so lens abberrations (such as the variation of refractive index with wavelength) are a major issue. The optical system shown above was a UK design, now widely used. The pictures below show this type of system in use at Ninewells Hospital, Dundee. Dr R Mountain of the ear, nose, and throat department showed me some of the spectacular images of his own body that could be produced using these systems.

The rigid endoscope used for viewing the throat
Dr Mountain viewing his larynx (vocal chords) via the rigid endoscope
The endoscope for viewing the ear is somewhat shorter. Note the illuminating light exiting the endoscope.
Here is the semi-transparent ear-drum, with the ear-bones behind it. Some hairs are visible in the outer ear.

Flexible endoscopes are used to go down natural tubes in the body. These can relay an image via a bundle of fibre optics, as shown below. In this case, it is important that the fibres transporting the image have the same relative arrangement at the two ends of the tube. The diagram also shows another bundle of fibres, which is used for putting light down into the body for illumination. This sort of endoscope (and others) often has a channel for inserting an operating tool. In the diagram below this takes the form of a single optical fibre used to irradiate a part of the body with intense laser light.

The picture above shows a short flexible endoscope being used to look inside the nasal cavities. More recently, endoscopes have been made with a miniature camera at the end of the endoscope, with the image transferred up to the operator electronically.

The medical team at Ninewells hospital in Dundee are renowned for their work in "keyhole" surgery, where endocopes are used to view what is happening, and the surgeon performs the procedure using tools inserted and maneeovered at the end of a long tube. One of the research teams at St Andrews is working with Professor Sir Alfred Cushieri to develop optical techniques to improve the detection of early cancers.