Contrast Media used in Radiology
Contrast agents are the chemical substances which are introduced in the human body to enhance the visualization of internal structures that are not seen in plain radiography. In radiography contrast agents are used to improve the subject contrast. These agents are very important for the visualization of structures that cannot be seen under normal circumstances, by the use of contrast agents, organs can be seen with greater detail. Contrast agents are used because soft tissues are having low absorption /interaction ratio. Contrast media and the surroundings absorbs more number of X ray photons to make that portion of body more visible. The use of contrast agents should be determined on an individual basis according to the clinical circumstances of each patient.
Types of the contrast media:
- Negative contrast media
- Positive contrast media
Positive contrast media includes iodine and barium while negative contrast media include oxygen, carbon dioxide and air.
Iodine based contrast agents are among the most commonly used injectables in radiology today. Modern iodinated contrast agents can be used almost anywhere in the body. Most often they are used intravenously but can be administered Intraarterially, intrathecally, and intraabdominally. They are usually safe and adverse effects are moderate, mild and severe.
Properties of Contrast media: The X-ray contrast agents are insoluble barium sulfate for the diagnostic evaluation of the GI tract and water-soluble CM for the radiological assessment of the different vascular systems, body cavities and organs.Water-soluble Contrast media based on tri-iodobenzene is the alternative agent of choice for oral use when barium sulfate is contraindicated.
Ideal contrast media should be::
- Least toxic
- Less viscous
- Less osmolar
- Low surface tension
- Radio –opaque
Barium is used in the form of insoluble sulfate for the imaging of the GI tract. If perforation is suspected, then, only water-soluble, iodinated contrast agents (Gastrografin, Ultravist-370) can be used since the body is incapable of eliminating barium sulfate once it has entered the peritoneum. Barium sulfate is available either in a powder form which can be prepared directly before use or as a ready-to-use suspension. For double-contrast examinations (filling of the lumen with gas, coating of the wall with barium sulfate), barium sulfate is either mixed with a carbon dioxide additive or a gas-forming agent is taken in addition.
Iodine based contrast media:
The first Contrast Media on the basis of ionic tri-iodobenzene were introduced around 1950. Iodine is the only chemical element which combines three properties essential for the production of a successful Contrast agent, high contrast density, chemical behaviour which allows firm binding to the highly variable benzene molecule and low toxicity.
List of studies using contrast agents: