X-ray contrast agents are drugs that are distinguished by their ability to absorb x-rays from biological tissues. They are used to visualize the structures of organs and systems that are not detected or poorly studied in conventional radiography, CT and fluoroscopy.
The essence of such a study
A necessary condition for radiographic examination of pathological changes in organs is the presence of a sufficient degree of radiopaque substances in organs and systems. The passage of rays through the tissues of the body is accompanied by their absorption of one or another part of the radiation.
If the level of absorption of x-ray radiation by the tissues of the organ is the same, then the image will also be uniform, that is, structureless. With conventional fluoroscopy and radiography, the outlines of bones and metallic foreign bodies are visible. Bones, due to their phosphoric acid content, absorb rays much more strongly and therefore appear denser (darker on the screen) than the surrounding muscles, blood vessels, ligaments, etc.
The lungs during inspiration, in which there is a large amount of air, weakly absorb x-rays and, therefore, are less pronounced in the image than the dense tissue of organs and blood vessels.
The organs of the gastrointestinal tract, blood vessels, muscles and tissues of many organs almost equally absorb radiation. The use of certain contrast agents changes the degree of absorption of X-rays by organs and systems, that is, it becomes possible to make them visible during the examination.
Primary requirements
X-ray contrast agents must meet the following requirements:
- harmlessness, that is, low toxicity (there should be no pronounced local and general reactions as a result of the introduction of a contrast solution);
- isotonicity with liquid media with which they should mix well, which is especially important when they are introduced into the bloodstream;
- easy and complete removal of contrast medium from the body unchanged;
- the ability, if necessary, to partially accumulate, and then be removed in a short time by certain bodies and systems;
- relative ease of manufacture, storage and use in medical research.
Types of radiopaque compounds
Substances that can form a contrast image on a radiograph are divided into several types:
- Substances with low atomic mass - gaseous substances that reduce the absorption of x-rays. They are usually administered to determine the contouring of anatomical structures into hollow organs or body cavities.
- Substances with high atomic weights are compounds that absorb x-rays. Depending on the composition, radiopaque substances are divided into iodine-containing and iodine-free preparations.
In veterinary practice, the following low atomic weight radiopaque preparations are used: nitric oxide, carbon dioxide, oxygen and room air.
Contraindications to contrast enhancement
This type of study is not recommended for those who have individual iodine intolerance, previously diagnosed renal failure, diabetes mellitus or thyrotoxicosis. X-ray examination of the digestive tract is prohibited if the patient has a suspicion of perforation. This is due to the fact that free barium is an active irritant in relation to the peritoneal organs, and water-soluble contrast is less irritating.
Relative contraindications to the study using a contrast medium are acute diseases of the liver and kidneys, active tuberculosis and a tendency to allergies.
Methods of X-ray contrast studies
X-ray contrast diagnosis can be positive, negative and double. For positive studies, an X-ray positive contrast drug with a large atomic mass is introduced, while negative studies include the use of a negative drug with a small atomic mass. Double diagnostics are carried out with the introduction of both positive and negative drugs at the same time.
Composition of contrast agents
Today, there are radiopaque substances such as:
- water mixture based on barium sulfate (activators - tannin, sorbitol, gelatin, sodium citrate);
- solutions containing iodine (iodized oils, gases).
For diagnostics, special substances are used that contain polarized atoms with a high reflective property. These drugs are administered intravenously.
Study Preparation
Such studied areas as the skull, brain, paranasal sinuses, temporal lobes and chest organs do not require special preparation of patients for radiography. Before introducing a radiopaque substance in order to study bones and joints, pelvic organs and the abdominal cavity, kidneys, pancreas, vertebrae and intervertebral discs, it is necessary to prepare a person.
The patient must inform the medical staff about previous illnesses, recent surgical interventions, the presence of foreign bodies in the study area. Before the day of intravenous administration of radiopaque substances, it is advisable for patients to limit themselves to a light breakfast. For constipation, it is worth taking a laxative the day before, for example, Regulax or Senade.
X-ray recognition steps
X-ray studies are carried out in specially equipped rooms in a clinic or diagnostic center. You can get pictures, that is, the result of the examination, using a special device. Fluoroscopic studies begin with the identification of deviations in the studied areas. The next stage is a contrast polypositional study, that is, a combination of radiography and fluoroscopy. Of great importance in the study of organs and tissues is the diagnosis of the general appearance of the contrasted area.
Any administration of a radiopaque substance should be carried out according to the strict indication of the attending physician. Before the procedure, the medical staff must necessarily explain to the patient the purpose of the diagnosis and the algorithm of the study.
The medical kit for the administration of radiopaque substances includes:
- a device for intravenous administration of contrast;
- syringes and containers for radiopaque solutions.
The volume of syringes can range from 50 to 200 ml. In each case, a kit for introducing contrast before diagnosis is selected individually. Syringes for radiopaque substances should be fully compatible with the automatic injector.