The contrast media

From a practical point of view, it is convenient to divide contrast media into four main categories:

Contrast media for the digestive tract
Biliary elimination contrast agents
Renal elimination contrast media
Contrast media for lymphography

Contrast media for the digestive tract

The most used is barium sulphate, which is an insoluble salt, therefore not absorbable, which as such passes through the digestive tract unaltered, from which it is then eliminated. Its toxicity is therefore null, even if there are situations in which its use is contraindicated, such as in cases of intestinal perforation (because if this compound penetrates into the peritoneum it can cause complications) and in acute bowel occlusions.

The barium sulphate is administered by mouth and allows the opacification, therefore the study, of various parts of the digestive tract (esophagus, stomach and small intestine). The study of the colon gives better results if performed with a barium enema. Today, the The ideal examination technique for both types of application involves the simultaneous administration of a contrast medium with barium and gas, thus carrying out the double contrast study.
In addition to barium sulphate, water-soluble contrast media are also available for the study of the digestive tract, which are selectively used in the case of suspected perforation since, unlike barium, if they penetrate the peritoneum they do not create problems.

Biliary elimination contrast agents

They are the basis of radiological investigations for the study of the biliary tract. These are iodized compounds which, introduced orally or injected into a vein, are absorbed by the intestine, reach the liver and are eliminated from it through the bile, which is opaque in the radiological image.

Renal elimination contrast media

Those used today are called "third generation" and are non-ionic (ie hydrophilic) compounds with very low toxicity. They travel the bloodstream and are eliminated by the kidney. In the case of impaired renal function, other organs can take on a vicarious function in the elimination of this type of contrast (liver, small intestine, salivary glands). of the urinary system, allow the study of arterial and venous vessels; they are therefore the basis of techniques such as arteriography and venography, respectively. They are also used in various applications in CT of the brain, thorax, abdomen and pelvis, in radiography of the spinal cord (myeloradiography), of the joints ( arthrography) and in that of the uterus and tubes (hysterosalpingography).

Contrast media in lymphography

Today the most used contrast medium is Lipiodol, which is formed by a mixture of fatty acids such as oleic, linoleic, palmitic and stearic, linked to iodine. The contrast medium, after being injected into a peripheral lymphatic vessel of the dorsum of the foot, initially fills the lymphatic vessels of the whole body and then the lymph nodes. It then soon leaves the lymphatic vessels remaining vice versa present in the lymph nodes for weeks and months. The contrast medium that does not remain in the lymph nodes passes into the venous system and then reaches the small pulmonary vessels, where it is trapped and then removed by the macrophages. The use of lymphography is mainly aimed at the research and study of tumors originating in the lymph nodes and of some tumors that have instead metastasized in the lymph nodes.