Thorotrast

An overview of Thorotrast, a contrast agent used in radiology

Thorotrast

A vial of Thorotrast

Thorotrast is a radiographic contrast agent that was widely used in the mid-20th century for angiography and other radiological procedures. It is a colloidal suspension of thorium dioxide, a radioactive compound, which provided excellent contrast in X-ray imaging. However, its use was later discontinued due to its long-term health risks.

History

Thorotrast was introduced in the 1930s and quickly became popular due to its superior imaging qualities compared to other contrast agents available at the time. It was used extensively in cerebral angiography, hepatic imaging, and splenic imaging.

Composition and Properties

Thorotrast consists of thorium dioxide particles suspended in a liquid medium. The high atomic number of thorium (90) makes it highly effective at absorbing X-rays, thus providing excellent contrast in radiographic images. However, thorium is a radioactive element, and Thorotrast emits alpha particles, which can cause significant biological damage over time.

Health Risks

The primary health risk associated with Thorotrast is its radioactivity. Once injected, Thorotrast particles are phagocytized by the reticuloendothelial system, particularly in the liver, spleen, and bone marrow. The alpha radiation emitted by thorium can cause DNA damage, leading to an increased risk of cancer, particularly liver cancer, leukemia, and angiosarcoma.

Discontinuation

Due to the long-term health risks, Thorotrast was gradually phased out in the 1950s and 1960s as safer, non-radioactive contrast agents became available. The recognition of its carcinogenic potential led to the development and adoption of alternative contrast media, such as iodinated contrast agents.

Legacy

The use of Thorotrast has had a lasting impact on the field of radiology and medical imaging. It highlighted the importance of evaluating the long-term safety of contrast agents and spurred research into safer alternatives. The lessons learned from Thorotrast have informed the development of modern contrast agents and the regulatory processes that govern their use.

Related pages

• Radiology
• Contrast agent
• Radiation-induced cancer
• Iodinated contrast media