Abstract
A method is given for radiographing internal tissues, using the scatter from a narrow pencil of high-energy X-rays. A focusing collimator, made up of a number of lead cones, accepts scatter from a small volume at a fixed distance along the axis. The rays are counted by means of a large crystal and photomultiplier, whose output is used to modulate the brightness of a C.R.T. spot. The X-ray beam and C.R.T. spot scan in sympathy, so that a picture is built up of the density distribution in the focal plane of the collimator.
The present small-scale experiments are described, showing radiographs obtained from rabbits and guinea-pigs. The problems of a large-scale apparatus are examined, and it is concluded that the use of a linear accelerator would enable 10 cm × 10 cm scans to be achieved in 6 sec, resolving density differences as low as 1% and with an absorbed dose of 0·1 rads to the patient.