X-RAY FILM CASSETTE

Typical Number in Hospital:

Cost Bands:

References: 7

Although X-rays will produce an image on photographic film, the effect is inefficient, and most of the rays pass straight through. In practice, X-ray film is exposed by light emitted by fluorescent (intensifying) screens held in contact with the front and back of the film in a special cassette.

The light-tight film cassette is made up of several layers. There is a thin plastic sheet on the side which faces the patient and X-ray tube, and beneath this there is a thin fluorescent layer. This layer absorbs the X-rays more strongly than the film and produces a fluorescent image which is transposed to the photographic emulsion on the upper side of the film. X-ray film is dual sided, and so a second fluorescent layer (thicker than the first) is beneath the film. There may be a lead foil layer next, which is particularly important if cassettes are stacked in the magazine of a rapid cassette changer.

It is most important that there is intimate contact between the film and the fluorescent screens if a sharp image is to formed. Some cassettes include a secondary radiation grid for situations where a moving grid is not being used.