CiteWeb id: 20140000024

CiteWeb score: 2474

This article describes a technique in which X-ray transmission readings are taken through the head at a multitude of angles: from these data, absorption values of the material contained within the head are calculated on a computer and presented as a series of pictures of slices of the cranium. The system is approximately 100 times more sensitive than conventional X-ray systems to such an extent that variations in soft tissues of nearly similar density can be displayed. For many years past, X-ray techniques have been developed along the same lines, namely the recording on photographic film of the shadow of the object to be viewed. Recently, it has been realized that this is not the most efficient method of utilizing all the information that can be obtained from the X-ray beam. Oldendorf (1961) carried out experiments based on principles similar to those described here, but it was not then fully realized that very high efficiencies could be achieved and so, picture reconstruction techniques were not fully developed. As the exposure of the patient to X rays must be restricted, there is an upper limit to the number of photons that may be passed through the body during the examination, and so to the amount of information that can be obtained. It is, therefore, of great importance that the method of examination ensures that all the information obtained is fully utilized and interpreted with maximum efficiency. In the conventional film technique a large proportion of the available information is lost in attempting to portray all the information from a three-dimensional body on a two-dimensional photographic plate, the image superimposing all objects from front to rear. In order that any one internal structure may be seen, it must clearly stand out against the variations of the materials in front and behind it. The technique to be described divides the head into a series of slices, each being irradiated via its