COLD LIGHT SOURCE

Typical Number in Hospital: 10

Cost Bands: 3,4

References:

Direct viewing in the orifices and internal cavities of the body by endoscopy requires a light source. These used to be tiny bulbs mounted on the tip of the endoscope which had to work inside the body. Nearly all endoscopes now employ a flexible fibre-optic bundle to carry light from an external source to the tip of the endoscope. The instrument for providing the light is often called a cold light source. It is not in fact cold at all but is usually a high-power tungsten filament lamp with fan cooling. However, the light delivered along the endoscope is cold.

Much higher levels of illumination inside the body can be achieved using fibre-optic transmission than was previously possible, which improves the surgeon's view, and also gives a correct representation of colour. This is important in some applications (e.g. in the bladder) where diagnosis may be influenced by the colouring of the tissues examined.

Inside the light source there is a condenser and focusing system to present the light to the fibre bundle leading to the endoscope. The bundle normally has a special termination which may be a bayonet or push fit into a socket at the focal point of the lens system. Flash photography is possible if the light source contains xenon flash apparatus which can be focused onto the bundle socket.

Cold light sources are normally found in operating theatres but they may also be found in clinics where endoscopy is performed without general anaesthetic.

ITRX

COLLIMATOR r=3,7

A collimator is a device for restricting and directing X-rays or other radiation by simply passing the rays through a tube (or set of parallel or divergent tubes), a cone, diaphragm, or grid made of metal which strongly absorbs the rays.

In nuclear medicine collimators are encountered as a metal, usually lead, attachment to the crystal in a gamma camera. Gamma rays are not electrically charged and so cannot be focused or directed on to the crystal, and so they are directed through a series of holes in the collimator. The rays which do not pass through holes are absorbed in the metal. A crude focusing can be effected by arranging tapered holes so that only rays from a single point can reach the crystal. The effect is enhanced by having a large number of small holes arranged in rings (e.g. 7, 19, 37, etc.) although the sensitivity may be reduced if the total surface area of hole is reduced as well. If the organ to be scanned is not at a well-defined depth a parallel hole device may be preferred, and usually a number of different collimators is available. Collimation is more effective at lower energies of rays since high-energy rays are less absorbed in the metal.

Collimators are also used in radiotherapy to confine the treatment beam to the area to be irradiated. In this case they are single-hole collimators which may also form part of an applicator to define the distance from the source to the skin.

In diagnostic radiology the X-ray set is fitted with a collimator to limit the maximum field size, and diaphragms are fitted to allow the operator to select the field size and position.