Medical research and diagnostics

Magnetic resonance imaging (MRI) of the eye orbits and optic nerves

MRI or magnetic resonance imaging is one of the most common methods for diagnosing internal organs and tissues of living organisms. The study is based on measuring the electromagnetic response of atoms of a hydrogen nucleus. One of the areas of tomography diagnostics is ocular orbits and optic nerves. What you need to know about the study, how to prepare properly and what to expect from the procedure itself?

General characteristics of tomography

MRI allows you to study the human body based on the saturation of tissues with hydrogen and the features of their magnetic properties. Let's analyze the method of magnetic resonance imaging. The human body is almost entirely composed of water. Water, in turn, consists of 2 protons. The proton is in the back. This is the intrinsic angular momentum (motion index) of an elementary particle, which is equal to ½.

If this proton is placed in a strong alternating magnetic field, then it will begin to emit a radio wave. Each of these radio waves will be located and transmit a different frequency / intensity, depending on the location. A magnetic resonance imager captures these radio waves, due to which it finds the location of the proton itself. The equipment captures the signal from protons, processes them by special mechanisms and turns it into an image of the studied zone. Magnetic resonance imaging can be called a large magnet, but the "source" of protons will be the patient himself.

Contrast tomography is distinguished into a separate category. A special contrast agent is injected under the patient’s skin, which spreads through the blood stream and stains organs / blood vessels. What does it give? Contrast improves the information content / clarity of the picture, helps the specialist more easily and quickly navigate the diagnostic results. This type of MRI takes longer than the standard procedure. A contrast study should be performed on an empty stomach.

The advantages of MRI over X-ray and computed tomography

The price and demand for MRI is much higher than that of CT or X-ray. How is this justified?

Firstly, magnetic resonance imaging is considered an absolutely safe diagnostic method. Computed tomography and x-rays are based on x-ray radiation, which can harm the human body. The radiation load of the x-ray is much higher, so it is permissible to do it only a few times a year. On modern computed tomographs, radiation load is reduced, therefore, the time frame between diagnostics is less.

Secondly, MRI gives a more informative result. An x-ray is a flat image that only visualizes dense tissue. Magnetic resonance and computed tomography scans absolutely all tissues, gives a three-dimensional image, measures the temperature, allows you to evaluate a specific section in detail.

Some experts prefer CT in terms of information. Layered shooting using complex algorithms really gives a complete understanding of what is happening inside a living organism. But the selection of diagnosis depends on a number of features of the patient, the disease and the area being examined. In general, MRI is considered the safest and most informative method. Its only drawback is the price. It is justified by the high cost of equipment and the need for its constant maintenance.

What you need to know about the study area?

The human visual system is not limited to the visual apple. This is a whole multi-component system that functions as a coherent mechanism. The optic nerve and ophthalmic orbits also belong to this mechanism.

The optic nerve is the second pair of cranial nerves. They transmit the signal from the retina to the brain and help us navigate the outside world. The nerve itself has an atypical structure and development. It is more like cerebral white matter, which is associated with the nuclei of the diencephalon and the cerebral cortex.

What clinical manifestations should be diagnosed? Even a slight decrease in vision may indicate problems with the optic nerve. Perhaps its conductivity is impaired or a certain section of fibers is affected, which limits the field of view. Visual hallucinations, regardless of the etiology, should also be the reason for contacting a specialist.

The eye sockets or orbits are the paired cavity in the skull. It is in it that the eyeball with appendages is located. The orbit volume of an average adult is 30 ml, of which 6.5 ml is reserved for the eyeball. MRI will help track the state of the orbits, diagnose congenital or acquired abnormalities. Among them are various defects, the result of mechanical damage, oncological neoplasms, inflammatory processes and so on.

Indications / contraindications to the procedure
IndicationsRelative contraindicationsAbsolute contraindications
Mechanical injuries of the eyeball (for example, foreign objects or the effects of shock)The presence of tattoosThe presence of a pacemaker (may affect the magnetic waves of MRI equipment, distorting the diagnostic result)
Inflammatory / infectious process in one or more elements of the visual systemDecompensated heart failureThe presence of ferromagnetic / electronic middle ear implants
Suspicion or diagnosis of thrombosisFirst trimester of pregnancyThe presence of a ferromagnetic apparatus Ilizarov
A sharp decrease in visual acuity, pain / discomfort in the eyes, regardless of etiologyClaustrophobiaExcessive excess weight (depends on the maximum weight that the equipment can support)
Diagnosis before and after surgical exposure to the organs of the visual systemSevere or extremely serious condition of the subject
Suspicion or diagnosis of cancerMental illness of the patient
Blood supply problems that affect the functionality of the organs of visionThe presence of dentures or braces
Diagnosis of the condition of the optic nerveHemostatic clips, prosthetic heart valves, insulin pumps
Diagnosis of the development of metastases that have penetrated the tissues of the organs of vision

Contrast MRI is contraindicated in pregnancy (regardless of duration), chronic renal failure, hemolytic anemia and individual intolerance to contrast drugs.

Why are tattoos, braces and metal devices considered contraindications?

MRI is a large magnet that can attract metal elements. The person within whom these elements are located can feel extremely unpleasant sensations - from slight discomfort to serious pain. It depends on the amount and characteristics of the metal inside. In addition to implanted iron, before diagnostics, it is necessary to remove all metal objects and design elements - earrings, a belt, etc.

What is wrong with tattoos? Even 20 years ago, ink tattoos contained small metal enzymes. In modern tattoo parlors, this practice has become the exception, and not the rule, which is always warned by the client. A patient with a metallic tattoo on his body will feel tingling, pain, or itching during diagnosis. Magnetic fields literally pull metal enzymes from the ink, which leads to unpleasant symptoms. The response of patients may be specific - some do not feel pain, others interrupt the procedure due to an unbearable feeling.

Metallized substances can distort the results of MRI. In order not to waste time and material resources for nothing, be sure to inform your doctor and tattoo availability. He will determine the presence / absence of metal particles and select an alternative diagnostic method.

Preparation and conduct of MRI

In most cases, the scan is carried out by a laboratory assistant. Before starting the diagnosis, he must pass the medical documentation. It includes a referral to magnetic resonance imaging, preliminary detention from a doctor and specific instructions. On the basis of medical documentation, the laboratory assistant sets up the device and determines the further course of events.

The patient is checked for the presence of metal objects, tattoos and medicinal plasters, then they are given a general briefing, if necessary, they inject a contrast medium and begin the procedure. An MRI device makes an extremely loud and unpleasant noise, so each patient is given special protection - ear plugs or headphones. The duration of the procedure may vary, but on average is 20-30 minutes.

Before starting the manipulations, be sure to check with the laboratory assistant how long the scan will take, where the call button is located and how you can contact the staff during the scan. This should be clarified in case of force majeure, if you feel unwell or want to stop the diagnosis for other reasons.

The tomograph itself looks like a big circle with a pull-out table. It is on this table that the patient is fixed with the help of fixing straps in a fixed position. It is important that during the diagnosis the patient does not make unnecessary movements so as not to distort the information content of the image. As soon as a person has fixed himself on a pull-out table, the laboratory assistant sets the tomography ring at the desired point and leaves for the next office to monitor the scan. From this moment, the laboratory assistant and the patient can only communicate via the speakerphone mounted in the room.

At the end of the study, the laboratory assistant helps the patient to get rid of the clamps and asks to wait at the office. MRI results are transmitted 30-60 minutes after the procedure in DICOM format. The time frame may vary, depending on the workload of the medical staff.

Evaluation of the results

MRI assesses the condition of muscles, nerves, blood vessels, and various structures that are exposed to a magnetic field. Tomography helps to identify cancerous tumors, infectious or inflammatory processes, structural tissue disorders, and more. Interpretation of the results should be carried out by a radiologist or laboratory assistant who conducts the study. He writes out a conclusion and issues it together with an MRI image to the patient’s hands. Additionally, a film is issued with a sequential image of sections of the orbits. In some clinics, information can be duplicated on electronic media at the request of the patient. Then, the medical documentation is transferred to the attending physician, who issued a referral for MRI. He compares the condition of the organs with complaints / other studies, makes an accurate diagnosis and develops a further therapeutic course.

Magnetic resonance imaging is one of the most informative and safe diagnostic methods. It is permissible to use it even for young children, and in some cases for pregnant women. Tomography can be done not only as prescribed by a doctor, but also as a prophylaxis for all body systems. The main thing is to strictly follow the instructions of the medical staff and be healthy.

Watch the video: how to read mri of orbit (December 2019).