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Instant radiographs can be produced by the same process as used in the Xerox photocopier. A thin semiconductive layer of amorphous selenium is charged up to a high voltage (600-1200 V). When this layer is exposed to light (or X-rays) the exposed areas become conductive and transfer the charge to an aluminium plate beneath. An aerosol of negatively charged particles is then attracted on to the remaining charged areas, and these particles are then baked on to paper. This paper then has the X-ray image without further development.
Although there is an advantage in having instant radiographs the technique has not become popular because the radiation exposure required is much higher than with conventional radiographs, and there are a number of defects in the image which are well known in photocopiers, such as excessive contrast and edge enhancement. The high contrast can, however, be useful for imaging areas of low subject contrast, such as breasts, soft tissues, calcifications, and hair-line fractures.
Content and Design Copyright 2000 Dr. Malcolm C Brown. See Title Page for more details