Discrimination between thorotrast and iodine contrast medium by means of dual-energy CT scanning.

A dual-energy CT scanning method is proposed to discriminate between thorotrast and iodine contrast medium in patients suspected of having thorotrast deposits in the spinal canal as a consequence of myelography injections. The ratio of CT numbers at two X-ray tube voltages was used to distinguish the two materials in the analysis of dual-energy CT scanning. The K-edge of thorium was used to enhance the discrimination sensitivity. Theoretical analysis predicted the feasibility of the method and this was verified by experiment. The sensitivity for the discrimination between thorium and iodine is much higher than that achieved by the gamma-ray counting technique using a whole-body counter. This method, the ratio of CT numbers at two kV values, may be useful in other clinical applications.