Italian physician Luigi Bogliolo conducted clinical trials demonstrating the carcinogenicity and potentially lethal effect of Thorotrast (ThO2), used as a contrast agent for x-rays and angiograms (which study blood vessels). Today, Thorotrast is known to be one of the most potent carcinogens known. It would continue to be used throughout the world throughout the 1930s and 1940s, and in the United States again in the 1950s.
