Thorium dioxide, a main component of Thorotrast that was used as a contrast agent for cerebral angiography. Thorotrast is an alpha emitter and primary site of deposition is the reticuloendothelial system including the liver, spleen, bone marrow, and lymph nodes. However was discovered, that this compound can cause hepatic angiosarcoma with a long latent period. That is why this contrast agent was withdrawn.