The E.M.I. scanner is a machine which employs a method of X-raying patients whereby the information obtained from the X-rays is fully utilized. The high sensitivity thus obtained enables the machine to differentiate between the various organs of the body which are presented in three-dimensional form as a series of tomographic slices. The machine scans through the patient in a transaxial plane with a narrow beam of X-rays. A bank of detectors measures the transmission through the body as it scans across the plane and this is repeated at many different angles through the plane. The readings obtained from the detectors are passed to a computer which mathematically reconstructs a picture of absorption values of the slice.