What is "thorotrast"

n. A contrast medium composed of a suspension of thorium dioxide

Thorotrast is a suspension containing particles of the radioactive compound thorium dioxide, ThO, that was used as a radiocontrast agent in medical radiography in the 1930s and 1940s. (Use in some countries, such as the U.S., continued into the 1950s.)

Thorium compounds produce excellent images because of thorium's high opacity to X-rays (it has a high cross section for absorption). Unfortunately, thorium is retained in the body, and it is radioactive, emitting harmful alpha radiation as it decays. Because the suspension offered high image quality and had virtually no immediate side-effects compared to the alternatives available at the time, Thorotrast became widely used after its introduction in 1931. ( António Egas Moniz contributed to its development.). About 2 to 10 million patients worldwide have been treated with Thorotrast. However, today it has shown an increase risk in certain cancers such as cholangiocarcinomas and angiosarcomas of the liver.