Medical research and diagnostics

Magnetic resonance imaging (MRI) of limb vessels

Limbs - paired appendages of the body in animals. They are detached from the trunk / head and provided with special muscular strength. Limbs are responsible for support, movement, grasping, touch, collection and processing of information. In order for the system to work efficiently, it needs to be fed with useful nutrients, energy and blood. The last vessels involved. These are elastic tubes that are placed all over the body and move blood through the body. Arteries, arterioles, capillaries, venules, and veins are prone to periodical cluttering, clogging, or inflammation. To track unwanted processes, doctors recommend to undergo an MRI. What you need to know about the scanned area, how exactly the procedure goes and how to prepare for the study?

General characteristics of the study area

Limbs - appendages of the body that are responsible for motor function. In humans, these include the hands and feet. The functionality of the limbs is possible not only due to the muscles, bones, several types of tissues, but also blood vessels. These are elastic tubular formations that permeate all parts of the body and are responsible for the movement of blood through the body. The scheme of the blood flow is as follows: blood flows to organs and tissues through the arteries, arterioles, and capillaries, and from them blood flows through the venules and veins to the heart.

Blood vessels are located throughout the body, but each of them differs in tissue composition, diameter and functional features. Let us examine in more detail the main types of elastic tubes. Arteries are vessels through which blood moves from the heart. They are characterized by thick walls with muscle, collagen and elastic fiber. Arteries are as plastic as possible and can expand / contract depending on the amount of blood. Blood circulating in the arteries is saturated with oxygen. The only exception is the pulmonary artery, venous blood flows through it.

In the extremities, blood circulates through the following arteries: digital, radial, brachial, axillary, dorsal digital, arcuate, anterior / posterior tibial, fibular, popliteal, femoral.

Arterioles are small arteries that precede capillaries. The arteriole vascular wall consists of muscle fibers. This allows the vessel to change the size of the lumen and to resist. Capillaries - the smallest blood vessels. In the human body, there are about 40 billion. Through the capillary walls, oxygen and nutrients pass from the blood to the cells, and carbon dioxide and other waste products pass from the cells to the blood.

Venules are small blood vessels that are responsible for blood circulation with an abundance of waste products and lack of oxygen from the capillaries into the vein. Veins - the vessels through which blood moves to the heart. The walls of the veins are much thinner than the walls of the arteries, they have fewer elastic elements and muscle fibers.

In the extremities, blood circulates through the following veins: palmar finger, ulnar, lateral subcutaneous, median, medial subcutaneous, axillary, dorsal finger, anterior / posterior tibial, small subcutaneous, popliteal, femoral, large subcutaneous.

The principle of operation of the magnetic resonance imager

MRI uses a fluid-filled tissue reaction to a magnetic field. How does it look from a practical point of view? The human body is more fluid. One of the components of water - the elementary particles of protons. If you place the proton in a strong magnetic field, it will begin to emit radio waves. Each wave is unique because it has its own frequency and intensity. These characteristics depend on the location of the proton. For example, a radio wave emanating from the shoulder joint will be significantly different from the one that comes from the lower limbs.

How to get this magnetic field? The source of the magnetic field is the scanner itself. In addition, it is able to capture, process and transform the received information into a three-dimensional image of the scanned area. A tomograph is a whole software and hardware complex, each part of which is responsible for a specific set of commands and tasks.

Most often, a specific affected area is diagnosed, and not all parts of the body — the lower limbs, the shoulder / elbow / knee / ankle joint, the hands or the wrist. A full-body scan is necessary with a "check-up" (comprehensive verification of all body systems) or multiple cancer pathologies.

Magnetic resonance angiography

This is one type of MRI that is suitable for scanning blood vessels. Diagnostics is carried out on tomographs whose power indicators are higher than 0.3 T. The advantage of the method is its informativeness. Medical staff will be available as anatomical and functional features of blood flow, which will facilitate the diagnosis and the development of therapy. MRA is based on the difference between the signal of moving protons and the surrounding immobile tissues.

To improve the differentiation of blood vessels and improve the information content of the method using contrast agents. These are special preparations based on gadolinium, which are injected into the bloodstream before scanning. Gadolinium gradually spreads throughout the body, enhances the magnetic field (since it has a positive magnetic susceptibility) and improves the visualization of blood vessels in the final image.

The decision to conduct a contrast scan is a doctor. Before the study, the patient should pass allergy tests to exclude individual intolerance to the drug.

MRI indications / contraindications

Scanning is necessary to confirm such diagnoses:

  • decreased sensitivity of the limbs, discoloration (blanching or blue);
  • numbness, pain, partial exhaustion of muscle strength;
  • gangrene (death of the tissues of the human body, which is accompanied by rotting);
  • mechanical damage to blood vessels;
  • the presence of cancerous growths that develop inside the vessel or squeeze it;
  • pathology of veins / arteries (for example, arterial obstruction or venous insufficiency);
  • aneurysm (protrusion of the arterial or venous wall due to thinning or stretching).

Contraindications to the procedure are divided into several groups - absolute, relative and specific. Let us examine in more detail each group. The absolute includes the presence of prostheses, stimulants, implants and devices, which include metallized substances. They can affect the magnetic field, distorting the final result, so an MRI scan is unacceptable.

The decision to diagnose with relative contraindications is taken by the attending physician. These include:

  • pregnancy (in the early stages of pregnancy, the baby is advised to be protected from any exposure, including the magnetic field);
  • hemostatic clips;
  • claustrophobia, inadequate patient behavior or mental abnormalities (the person simply will not be able to follow the instructions of the technician and will disrupt the course of the study);
  • temporary deterioration of the condition (fever or persistent vomiting can also cause a transfer or failure of an MRI. Be sure to tell your doctor about this);
  • tattoos (provided that the ink contains metallized elements);
  • braces and dentures.

For contrast MRI, a separate group of specific contraindications is distinguished. The introduction of gadolinium is prohibited during pregnancy, regardless of the time / condition of the mother or child. Contrast penetrates the placental barrier, and its effect on the fetus is still poorly understood. Doctors advise not to risk the health of the baby and choose a more gentle diagnostic method. Also, the introduction of the drug is unacceptable in case of individual intolerance and impaired renal function. In the first case, the patient will develop a specific allergic reaction, in the second - there will be difficulties with the introduction of gadolinium from the body. Another contraindication to contrast tomography is hemolytic anemia (a rare blood disorder).

Preparation and methodology

Before scanning it is necessary to remove all metal objects and change into loose clothing (the patient brings it herself or receives it from a medical institution). The laboratory assistant studies the necessary documentation, preliminary diagnosis, history and specificity of the scan. After reading, he sets up the device, conducts a short briefing and helps the patient to sit on the retractable table of the scanner. The scan duration depends on the scan area. Diagnosis of the lower limbs will take longer than the study of the elbow joint. In general, the scan lasts from 20 to 45 minutes, but it is better to check the information with the laboratory technician.

Magnetic resonance tomograph produces loud noise. In most diagnostic centers, the patient is given earplugs or special headphones that will ensure maximum peace and comfort. If contrast is mentioned in medical records, the technician injects gadolinium intracutaneously into the scanning area.

Contrast can cause side effects. Possible effects include nausea, vomiting, fever, dizziness, and general malaise. Be sure to notify the laboratory technician or your doctor if the condition worsens after scanning.

Once all preparations have been completed, the medical officer leaves for the adjacent office to conduct the scan. From this point on, the connection between the patient and the laboratory technician is carried out through a signal button (located next to the tomograph) and a speakerphone, installed in the room. The patient can stop the diagnosis at any time by pressing the alarm button.

As soon as the device is started, the scanning ring will begin to rotate around the scanned area, creating a magnetic field and fixing the outgoing radio waves. Information about the intensity and frequency of radio waves enters the computer. Through complex mathematical problems, it is transformed into a layered, and then a three-dimensional image of a limb. The picture is displayed on the screen, printed or transmitted to the patient in electronic format. At the end of the scan, the laboratory technician returns to the office, learns about the patient's condition and asks to wait for the results outside the door. Usually, their processing takes from 20 to 60 minutes, depending on the workload of medical personnel. The laboratory technician examines the scans, makes a preliminary diagnosis, and redirects the patient back to the attending physician for more information.

Magnetic resonance imaging is one of the safest and most informative diagnostic methods. The equipment captures even the slightest deviation from the norm and provides a detailed image of the affected area. After the MRI, the patient can immediately proceed to the usual matters, specific adaptation is not required. The magnetic field does not affect the performance of the body, and the risk of side effects is extremely small. The main thing is to undergo an MRI only as prescribed by a doctor and be healthy!

Watch the video: Noncontrast MRA magnetic resonance angiogram neck radiology search pattern (December 2019).