Substance comparatively opaque to X-rays, which appears lighter on X-ray film and allows a body structure that does not normally contrast with its background to be seen clearly on the film. Common contrast media include barium sulfate and iodized organic compounds. They are given by the route that introduces them into the structure to be examined—swallowed or as an enema for the digestive tract, inhaled for the respiratory tract, or injected for blood vessels and for organs and tissues they supply. Serious reactions to contrast media are not infrequent. Seealso diagnostic imaging.
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Iodine based contrast media such as urografin or Omnipaque is used most commonly in radiology, due to its relatively harmless interaction with the body. It is primarily used to visualise vessels, but can also be used for tests of the urinary tract, uterus and fallopian tubes.
|Ionic||Diatrizoate (Hypaque 50)||Ionic Monomer||300||1550||High Osmolar|
|Ionic||Metrizoate (Isopaque Coronar 370)||Ionic||370||2100||High Osmolar|
|Ionic||Ioxaglate (Hexabrix)||Ionic dimer||320||580||Low Osmolar|
|Non-Ionic||Iopamidol (Isovue 370)||Non-ionic monomer||370||796||Low Osmolar|
|Non-Ionic||Iohexol (Omnipaque 350)||Non-ionic||350||884||Low Osmolar|
|Non-Ionic||Ioxilan (Oxilan)||Non-ionic||Low Osmolar|
|Non-Ionic||Iodixanol (Visipaque 320)||Non-ionic dimer||320||290||Iso Osmolar|
These often appear in the form of barium sulfate. Barium is mainly used in the imaging of the digestion system.
Negative contrast always occurs in a gas, usually as one of the following:
Examples of the use of negative contrast medium are as follows:
Although rare, it is possible to be allergic to contrast media. Reactions can range from minor to severe, in the worst case scenario, resulting in death.
Mild (no treatment necessary)
Moderate (treatment necessary, but no intensive care)
Severe (life-threatening, intensive care necessary)
Contrast media is never given to a patient unless a doctor is present to assist should an allergic reaction occur. Patients are usually screened before being given contrast, by means of a series of questions. These typically include an allergy history and a history of any asthma and diabetes.
It has been recommended that metformin, an oral antidiabetic agent, be stopped for 48 hours following the intravascular administration of contrast media and that the use of metformin not be resumed until renal function has been shown to be normal. The reasoning is that if the contrast medium causes kidney failure (as happens rarely) and the person continues to take metformin (which is normally excreted by the kidneys), there may be a toxic accumulation of metformin, increasing the risk of lactic acidosis, a dangerous complication.
However, guidelines published by the Royal College of Radiologists suggest this is not as important for patients who receive <100mls of contrast media and have normal renal function. If renal impairment is found before administration of the contrast, metformin should be stopped 48 hours before and after the procedure..