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Thorotrast is a suspension
Suspension (chemistry)

In chemistry, a suspension is a heterogeneous fluid containing solid particles that are sufficiently large for sedimentation. Usually they must be larger than 1 micrometre....
 containing particles of the radioactive compound thorium dioxide
Thorium dioxide

Thorium dioxide , also called thorium oxide is a white, crystalline powder. It was formerly known as thoria or thorina. It is produced mainly as a by-product of lanthanide and uranium production[1]....
, ThO2, used as a contrast medium
Contrast medium

A medical contrast medium is a substance used to enhance the contrast of structures or fluids within the body in medical imaging. It is commonly used to enhance the visibility of blood vessels and the gastrointestinal tract....
 in X-ray
X-ray

X-radiation is a form of electromagnetic radiation. X-rays have a wavelength in the range of 10 to 0.01 nanometers, corresponding to frequency in the range 30 Hertz to 30 Hertz and energies in the range 120 Electron volt to 120 keV....
 diagnostics in the 1930s and 40s (use in some countries, such as the U.S.
United States

The United States of America is a Federal government constitutional republic comprising U.S. state and a federal district. The country is situated mostly in central North America, where its Contiguous United States and Washington, D.C., the Capital districts and territories, lie between the Pacific Ocean and Atlantic Oceans, Borders of the U...
, continued into the 1950s).

The naturally abundant thorium nuclide 232Th
Thorium-232

Thorium-232 is the primary abundant nuclide of thorium. It is a slightly unstable radionuclide that is found in the earth's crust. It is a fertile material able to absorb a neutron and undergo Nuclear transmutation into a nuclide that is able to support nuclear fission ....
 is slightly unstable and decays through the emission of an alpha particle
Alpha particle

Alpha particles consist of two protons and two neutrons bound together into a particle identical to a helium atomic nucleus; hence, it can be written as He2+ or 42He2+....
.






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Thorotrast
Thorotrast is a suspension
Suspension (chemistry)

In chemistry, a suspension is a heterogeneous fluid containing solid particles that are sufficiently large for sedimentation. Usually they must be larger than 1 micrometre....
 containing particles of the radioactive compound thorium dioxide
Thorium dioxide

Thorium dioxide , also called thorium oxide is a white, crystalline powder. It was formerly known as thoria or thorina. It is produced mainly as a by-product of lanthanide and uranium production[1]....
, ThO2, used as a contrast medium
Contrast medium

A medical contrast medium is a substance used to enhance the contrast of structures or fluids within the body in medical imaging. It is commonly used to enhance the visibility of blood vessels and the gastrointestinal tract....
 in X-ray
X-ray

X-radiation is a form of electromagnetic radiation. X-rays have a wavelength in the range of 10 to 0.01 nanometers, corresponding to frequency in the range 30 Hertz to 30 Hertz and energies in the range 120 Electron volt to 120 keV....
 diagnostics in the 1930s and 40s (use in some countries, such as the U.S.
United States

The United States of America is a Federal government constitutional republic comprising U.S. state and a federal district. The country is situated mostly in central North America, where its Contiguous United States and Washington, D.C., the Capital districts and territories, lie between the Pacific Ocean and Atlantic Oceans, Borders of the U...
, continued into the 1950s).

The naturally abundant thorium nuclide 232Th
Thorium-232

Thorium-232 is the primary abundant nuclide of thorium. It is a slightly unstable radionuclide that is found in the earth's crust. It is a fertile material able to absorb a neutron and undergo Nuclear transmutation into a nuclide that is able to support nuclear fission ....
 is slightly unstable and decays through the emission of an alpha particle
Alpha particle

Alpha particles consist of two protons and two neutrons bound together into a particle identical to a helium atomic nucleus; hence, it can be written as He2+ or 42He2+....
. Thorium compounds produce excellent images because of thorium's high opacity to X-rays (it has a high cross section
Cross section (physics)

In nuclear physics and particle physics, the concept of a cross section is used to express the likelihood of interaction between particles.When particles are thrown against a foil made of a certain substance, the cross section is a hypothetical area measure around the target particles that represents a surface....
 for absorption). 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. 2–10 million patients worldwide have been treated with Thorotrast.

Even at the time of introduction, there was concern about the safety of Thorotrast. Following injection, the drug is distributed to the liver
Liver

The liver is a vital organ present in vertebrates and some other animals; it has a wide range of functions, a few of which are detoxification, protein synthesis, and production of biochemicals necessary for digestion....
, spleen
Spleen

The spleen is an organ found in all vertebrate animals. In humans, the spleen is located in the abdomen of the body, where it functions in the destruction of redundant red blood cells, and holds a reservoir of blood....
, lymph node
Lymph node

A Lymph node is an organ consisting of many types of cells, and is a part of the lymphatic system. Lymph nodes are found all through the body, and act as filters or traps for foreign particles....
s, and bone
Bone

Bones are rigid organ that form part of the endoskeleton of vertebrates. They function to move, support, and protect the various organs of the body, produce red blood cell and white blood cells and store minerals....
,where it is absorbed. After this initial absorption, redistribution takes place at a very slow pace. Specifically, the biological half-life
Half-life

The half-life of a quantity whose value decreases with time is the interval required for the quantity to decay to half of its initial value. The concept originated in describing how long it takes atoms to undergo radioactive decay but also applies in a wide variety of other situations....
 is estimated to be 22 years. This means that the organs of patients who have been given Thorotrast will be exposed to the alpha-radiation it emits for much of the rest of their lives. The significance of this exposure was not fully understood in 1931.

Due to the release of alpha particles, Thorotrast was found to be extremely carcinogenic. There is a high over-incidence of various cancers in patients who have been treated with Thorotrast. The cancers occur some years (usually 20-30) after injection of Thorotrast. The risk of getting liver cancer
Hepatocellular carcinoma

Hepatocellular carcinoma is a primary cancer of the liver. Most cases of HCC are secondary to either a viral hepatitis infection or cirrhosis ....
 (or bile duct cancer
Cholangiocarcinoma

Cholangiocarcinoma is a cancer of the bile ducts, which drain bile from the liver into the small intestine. Other biliary tract cancers include pancreatic cancer, gall bladder cancer, and cancer of the ampulla of Vater....
) in former Thorotrast patients has been measured to be well above 100 times the risk of the rest of the population. The risk of leukemia
Leukemia

Leukemia is a cancer of the blood or bone marrow and is characterized by an abnormal proliferation of blood Cell , usually white blood cells ....
 appears to be 20 times higher in Thorotrast patients. These observations have led some to characterize Thorotrast as the most potent human carcinogen
Carcinogen

The term carcinogen refers to any substance, radionuclide or radiation that is an agent directly involved in the promotion of cancer or in the increase of its propagation....
 known.

The Danish
Denmark

Denmark is a Scandinavian country in northern Europe and the senior member of the Kingdom of Denmark. It is the southernmost of the Nordic countries....
 director Nils Malmros
Nils Malmros

Nils Malmros , a Danish language film director and screenwriter, is considered a leading auteur of realism in Danish cinema. Malmros is noted for his detailed focus on the common growing pains of adolescence and the loss of innocence, which he draws from his childhood experiences growing up in ?rhus, Denmark....
's movie, Facing the Truth (original Danish
Danish language

Danish is one of the North Germanic languages , a sub-group of the Germanic languages branch of the Indo-European languages. It is spoken by around 6 million people, mainly in Denmark; the language is also used by the 50,000 Danes in the northern parts of Schleswig-Holstein in Germany where it holds the status of minority language....
 title At Kende Sandheden) from 2002, portrays the dilemma that faced Malmros's father, Richard Malmros, when treating his patients in the 1940s. Richard Malmros was deeply concerned about the persistence of Thorotrast in the body but was forced to use Thorotrast, because the only available alternative (per-abrodil) had serious immediate side-effects, suffered from image quality problems and was difficult to obtain during the Second World War. The use of Thorotrast in Denmark ended in 1947 when safer alternatives became available. Today, iodinated hydrophilic molecules are universally used as contrast agents for X-ray procedures.

Thorotrast has also been used in research to stain neural tissue samples for examination by historadiography
Historadiography

Historadiography is a technique formerly utilized in the fields of histology and cellular biology to provide semiquantitative information regarding the density of a tissue sample....
.