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Energy imparted to the patient during fluoroscopy using magnified fields of view

Regional Medical Physics Department, Newcastle General Hospital, Newcastle-upon-Tyne, NE4 6BE, UK

This excerpt was created in the absence of an abstract.

Most textbooks on radiological equipment contain the information that the gain of an X-ray image intensifier is proportional to the ratio of the areas of its input and output phosphors, but the practical implications of this in terms of dose to the patient appear to be less well known.

For the normal practice of performing fluoroscopy under automatic dose rate control, when switching to a magnified field of view the dose rate would be expected to increase in inverse proportion to the change in gain of the intensifier if a constant signal-to-noise ratio in the image is to be maintained. At the same time an automatic change in collimation should take place so that the radiation beam size is restricted to cover only the active portion of the intensifier input phosphor (NRPB, 1988).

Received for publication November 1, 1990. Revision received February 1, 1991.