Film-based dual energy radiography

摘要

X-ray energy-difference images are obtained simultaneously by exposing a body to a broad energy spectrum x-ray beam while a radiographic film package is disposed between front and rear x-ray intensifying screens. The film package has two superimposed films with a light-opaque sheet between them. The front screen, on which the polyenergetic image beam emerging from the body is incident, is excited to luminescence by x-ray photons predominantly in one energy band and the rear screen is excited predominantly by photons in another band. The light opaque sheet preferably contains x-ray filter material for additional filtering of photons to increase the fraction of photons at said other band to which the rear screen is sensitive. A shadowgraph of a marker is formed on the film emulsions during x-ray exposure to aid in matching congruent picture elements on each film when the developed films are being read out to obtain signals corresponding to their intensities. Notches in the edges of the films and sheet serve as a code for indicating the type of screens with which the package can be used.