TOMOGRAPHIC X-RAY UNIT

Typical Number in Hospital: 2

Cost Bands: 6,7

References: 7

This is a special form of diagnostic X-ray set which can produce an image of a particular layer within the body. The result differs from normal X-ray images on which all layers between the tube and the film are superimposed.

computerized tomography (CT scanning) has become possible in the last decade and uses a scanning technique employing narrow X- ray beams to assemble information on the X-ray absorption of each point within the scanning plane. An image of this absorption pattern is produced by computer (See CT scanner).

A more widely used technique causes blurring of all the structures above or below the layer under investigation by the correlated movement of any two of the tube, object (patient), and film. The most common movement is that of the tube and film with respect to the patient, who remains stationary. The tube and film are connected in such a way that they rotate about the plane to be imaged; thereby all other layers appear blurred on the image, and only interfere with the 'plane in focus' to a small extent. The tube and film may be made to undertake a number of different motions to produce the effect such as parallel linear, arcuate linear, circular, or spiral (helical) movement.

Since the exposure is usually taken over a longer period than for conventional X-ray imaging, the X-ray intensity is lower, and therefore special film and fluorescent screen combinations are used.