CT SCANNER

Typical Number in Hospital: 1

Cost Bands: 8

References: 3,7

Previously called the EMI scanner, and the CAT scanner, this is now known as the CT (computerized tomography) scanner. It produces an image on a CRT screen of a section through the body, with each point on the image having a brightness corresponding to the X-ray absorption properties of the point represented.

The scanner comprises one or more X-ray sources collimated to produce very thin X-ray beams which pass through the patient to a scintillation detector. The overall attenuation of the X- ray beam as it passes through the body is calculated from the intensity reaching the detector. Similar attenuation measurements are made thousands of times as the position and direction of the X-ray beam is changed. A computer with suitable programs calculates the attenuation occurring at each point within the section being scanned which would be necessary to account for the measured overall attenuations. A variety of different scanning methods, and arrangements of single or multiple heads and/or detectors, are in use.

The first and probably most important use of CT scanners was in brain scanning, but they are also used widely for imaging all parts of the body. An important advantage over conventional X- ray techniques is that soft tissues can be clearly seen and differentiated. A major improvement in recent years has been in the number of elements which can be resolved in the image, and shorter scanning times. Other developments have allowed the presentation of tomographic planes other than the axial section.