Quantitative Aspects of Television Techniques in Diagnostic Radiology

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Abstract
The idea of image intensification was first conceived as a method of increasing the screen brightness in fluoroscopy. Viewing would then be possible without dark adaptation, and perhaps the patient dose might be reduced. In addition, when it was realised that the poor quality of the screen image was due to deficiencies of the eye rather than of the screen, it was thought that more information would be visible in the image if the brightness were increased. All these objectives have been at least partially attained, but the process is now seen as one aspect of a much wider problem, that of extracting the maximum of information from the X-ray beam as it emerges from the patient. Two aspects of the diagnostic process are of great significance. First, the greater part of the X-ray energy in the incident beam is absorbed in the tissues, the transmitted energy flux being only one thousandth (for lateral abdominal projection) to one tenth (for antero-posterior chest) of that incident on the patient. It is therefore important both to reduce the output of the X-ray tube as far as possible to minimise undesirable biological effects, and also to use sensitive methods of detection to respond to the limited energy in the emergent beam. Second, the X-ray beam is composed of discrete quanta emitted from the target in random fashion, so the image received on the screen or other detector has a fine structure in which the quantum may be regarded as the unit of information.

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