Magnetic resonance imaging( MRI).Indications, contraindications MRI - Causes, symptoms and treatment. MF.
Apr 26, 2018
Magnetic resonance imaging( MRI) in the diagnosis of diseases
Magnetic resonance imaging( MRI) is a modern, safe( without ionizing radiation) noninvasive diagnostic method that provides a visualization of deeply located biological tissues, widely used in medical practice, particularly in neurology andneurosurgery.
Magnetic resonance imaging( MRI), as the name implies, is based on the phenomenon of nuclear magnetic resonance( NMR).The essence of this phenomenon in the general case boils down to the following: the nucleus of chemical elements in a solid, liquid or gaseous substance can be represented as magnets rotating rapidly around their axis. If these core magnets are placed in an external magnetic field, the rotation axes will begin to precess( i.e., rotate around the direction of the line of the external magnetic field), and the precession rate depends on the magnitude of the magnetic field strength. If now the sample to be irradiated with a radio wave, then if the frequency of the radio wave and the precession frequency are equal, resonance absorption of the radio wave energy by the "magnetized" nuclei will occur. After the irradiation of the sample has ceased, the atomic nuclei will go into their original state( relax), while the energy accumulated upon irradiation will be released in the form of electromagnetic oscillations, which can be registered with the help of special equipment.
Medical tomographs use NMR registration for a number of reasons on protons - the nuclei of hydrogen atoms that make up the water molecule. Due to the fact that the method used in MRI is extremely sensitive even to minor changes in the concentration of hydrogen, it can not only reliably identify different tissues, but also distinguish normal tissues from tumor tissues.
Magnetic resonance imaging( MRI) provides an accurate image of all body tissues, especially soft tissues, cartilage, intervertebral discs and brain. Even the smallest inflammatory foci can be detected on an MRI.Structures with low water content( bones or lungs) do not lend themselves to tomography due to poor image quality.
Advantages of Magnetic Resonance Imaging( MRI) over other methods of
Magnetic resonance imaging( MRI) allows you to obtain an image of virtually all body tissues, since it is possible to change the time of the radio wave flow.
Because magnetic resonance imaging provides a very detailed image, it is considered to be the best technique for detecting various tumors, examining disorders of the central nervous system and diseases of the musculoskeletal system. As a result of magnetic resonance imaging( MRI), a complete, three-dimensional picture of the area of the body is obtained. Thanks to magnetic resonance imaging( MRI), it becomes possible, without using contrast agents, to carefully examine many organs and systems.
Modern tomographs allow the scan engine to obtain tomograms in an arbitrarily oriented plane without changing the position of the patient. At the same time, the MRI study uses similar CT-principles of spatial coding of information and data processing. For one scan, for example, the head, data collection is usually performed from approximately 20 levels of the skull and brain with a cut thickness of 4-5 mm. The higher the magnetic field strength of the tomograph, this value is expressed in Tesla, the thinner these slices can be made, the more accurate the study, the more accurate the result will be .Most clinical magnetic resonance tomographs( MRI) contain 0.5-1.5 Tesla magnets and only a few have 3T.A stronger magnetic field can provide a more detailed examination. The scan time depends on the tasks and parameters of the magnetic resonance imaging and is on average from 2-7 minutes( for magnetic resonance imaging of the MRI of the head) to 60 minutes. Eventually, images of the cuts of the tissue under investigation, for example, brain tissue, appear on the display screen.
Magnetic resonance imaging( MRI) method makes it possible to visualize the sections of the skull and brain, vertebral column and spinal cord on the display screen and then on the X-ray film. Information allows to differentiate the gray and white matter of the brain, to judge the state of its ventricular system, subarachnoid space, to reveal many forms of pathology, in particular, volumetric processes in the brain, demyelination zones, foci of inflammation and edema, hydrocephalus, traumatic lesions, hematomas, abscesses, focidisorders of cerebral circulation by ischemic and hemorrhagic type, by the way, ischemic foci in the brain can be detected in a hypodensic form already in 2-4 hours after a stroke.
An important advantage of magnetic resonance imaging of MRI before CT is the possibility of obtaining images in any projection: axial, frontal, sagittal. This makes it possible to visualize the subtentorial space, the vertebral canal, to reveal the neurin of the auditory nerve in the cavity of the internal auditory canal, the pituitary tumor, the subdural hematoma in the subacute period, even when it is not visualized on CT.
Magnetic resonance imaging( MRI) has become the main method of detecting certain forms of anomalies: anomalies of the corpus callosum, Arnold-Chiari anomalies, foci of demyelination in the paraventricular and other parts of the white matter of the brain in multiple sclerosis.
Magnetic resonance imaging( MRI) earlier than on computed tomography( CT) reveals foci of brain ischemia, while they can be detected in the brainstem, in the cerebellum, in the temporal lobe. Magnetic resonance imaging( MRI) clearly shows contusion foci, brain abscesses and edema of the brain tissue.
An important role is played by magnetic resonance imaging( MRI) in elucidating the causes of dementia. At the same time, changes in brain tissue are often nonspecific and sometimes difficult to differentiate, for example, foci of ischemia and demyelination.
Valuable information is revealed on the MP-tomograms of the spine, especially on sagittal slices. In this case, structural manifestations of osteochondrosis, in particular, the state of the vertebrae and ligamentous apparatus, intervertebral discs, their prolapse and impact on the dura mater, spinal cord, ponytail, visualization of intra-vertebral tumors, manifestations of hydromyelia, hematomyelia and many other pathological processes are visualized.
The diagnostic potential of magnetic resonance imaging( MRI) can be increased by the preliminary administration of certain contrast media. As the contrast medium introduced into the bloodstream, an element from the group of rare-earth metals, gadolinium, which has the properties of a paramagnetic substance, is administered intravenously.
Advantage of magnetic resonance imaging( MRI) before computed tomography( CT) is most obvious when examining those parts of the nervous system that can not be imaged by CT due to overlapping of the brain tissue with adjacent bone structures. In addition, magnetic resonance imaging( MRI) can distinguish between inaccessible CT changes in brain tissue density, white and gray matter, detect brain tissue damage in multiple sclerosis, etc.
For magnetic resonance imaging( MRI), the patient is not exposed to ionizing radiation .However, for the application of magnetic resonance imaging( MRI) there are some limitations. Thus, magnetic resonance imaging( MRI) is contraindicated in the presence of metallic foreign bodies in the cranial cavity, since there is a danger of their displacement under the influence of the magnetic field and, consequently, additional damage to nearby structures of the brain. Contraindicated magnetic resonance imaging( MRI) in patients with external driver rhythm, pregnancy, pronounced claustrophobia( fear of being in a close room).Complicating the use of the MRI examination is its duration( 30-60 min), during which the patient should be stationary.
Indications for magnetic resonance imaging( MRI)
Indications for magnetic resonance imaging( MRI) and preparation for the study, see the relevant sections:
MRI of the brain or pituitary
MRI of the cerebral vessels angioprogram arterial
MRI of the cerebral vessels angioprogram venous
MRI of the spinal cord and of the spine: of the cervical spine
MRI of the neck vessels( extracranial arterial or venous program)
MRI of the spinal cord and spine: thoracic
MRI of the spinal cord and spine: lumbosacral
MRI of the adrenal gland
MRI of one joint, MRT lo MRI of the knee joint
MRI of the brain or spinal cord( including craniovertebral junction) with anesthesia
MRI of the abdominal cavity
MRI of the pelvic organs
Contraindications to magnetic resonance imaging( MRI)
Absolute contraindications to magnetic resonance imaging( MRI):
Metallic foreign body in orbit,
Intracranial aneurysms clipped with ferromagnetic material,
Presence of electronic devices( pacemaker, for example),
Hematopoietic anemia( with contrasting)
Relative contraindications to magnetic resonance imaging( MRI):
- External rhythm driver,
- severe claustrophobia or inadequate behavior,
- pregnancy( relative contraindication MRI is a pregnancy of up to 12 weeks, as currently collectedinsufficient evidence of a teratogenic effect of the magnetic field),
- intracranial aneurysms clipped with non-ferromagnetic material,
- metal protuberancesscars or fragments in non-scans,
- the inability to maintain mobility due to severe pain,
- tattoos containing metallic compounds,
- the need for constant monitoring of vital signs *,
- Drug or alcohol intoxication status
* Devices developedVentilators adapted for use in MRI rooms
Menstruation, the presence of an intrauterine device, and breastfeeding are not contraindications for research.
The final decision on a possible refusal to the patient for an MRI examination is taken immediately before the examination by the on-call doctor-radiologist MRI.
How is magnetic resonance imaging( MRI) performed?
The procedure for magnetic resonance imaging( MRI) is painless and does not require special preparation for the study, except for examination of pelvic organs. Before the examination, MRI should continue taking medications( if they are prescribed to you), it is recommended that a moderate intake of food be recommended. You offer a robe or you can have your things without metal zippers. Be sure to ask to remove all accessories - watches, jewelry, jewelry, hairpins, hairpins. Also remove the wig, denture, hearing aid. It is very important before MRT to remove from itself the subjects containing metal. Metal objects can disrupt the effect of the magnetic field, which is used during the survey, and the quality of the images may be poor. In addition, the magnetic field can damage the electronics.
You must tell your doctor if you have a metal joint prosthesis, an artificial heart valve, grafted electronic devices, electronic implants of the middle ear or implants in the dentition in your body. The presence of metal in your body can be risky for you, or act on a part of the MRI snapshot.
The method of magnetic resonance imaging( MRI) is to place the patient horizontally in a narrow tunnel of a tomograph, the time depends on the type of study. The patient should maintain complete immobility of the anatomical region under investigation.
Some MRI images are obtained by injecting a contrast solution through a vein in your arm. During the test, breathe quietly, do not move, you can talk with the MRI doctor through the microphone.
High-speed magnetic resonance tomographs( MRI machines) are shorter and wider, so most of your body is in the open state during scanning. The newer MRI machines are open from all sides, it can weaken the quality of the image, but such equipment is widely used for patients with claustrophobia and children.
To improve the diagnostic efficiency of magnetic resonance imaging( MRI), patients are advised to bring with them the data of previous MRI studies, other methods of radiation, laboratory or functional diagnostics, as well as outpatient maps or referrals from physicians with indication of the area and purpose of the study.
Magnetic resonance imaging( MRI) procedure is painless. The equipment itself for MRI during operation reproduces not a loud noise, which can cause an unpleasant sensation.
Personal belongings, jewelry and valuables, clothing containing metal and electromagnetic devices are not allowed in the MRI scan room.
Magnetic resonance imaging, like any study, has definite diagnostic limits, as well as possible limited sensitivity and specificity in the diagnosis of pathological processes. In this regard, as well as in case of doubt in the desirability of conducting a study, it is recommended to consult a doctor or a doctor of magnetic resonance imaging( MRI).
Magnetic resonance imaging( MRI) results
Upon completion of the examination, you may be asked to wait until the MRI images are examined and until you are sure that you do not need additional pictures. Then you go out and wait for the results of the MRI study.
Is magnetic resonance imaging( MRI) harmful?
At this time, it is not known about any dangers or side effects associated with magnetic resonance imaging( MRI).In magnetic resonance imaging, ionizing radiation( X-rays) is not used, it can be repeated. Theoretically, there is a small risk for the fetus in the first 12 weeks of pregnancy, so during this period, scanning for pregnant women is contraindicated. Since during the magnetic resonance imaging the patients must lie inside the large cylinder, some of them may show symptoms of claustrophobia. Patients who are afraid of a closed space should notify a doctor about this, in this case it is possible to invite a close relative to the magnetic resonance imaging( MRI) procedure.
Magnetic resonance imaging( MRI) continues to improve, its scope is expanding:
Magnetic resonance angiography
The vascular image is one of the innovations of MRI.MRI is a safe way to assess the condition of arteries and veins throughout your body. This procedure does not require the introduction of a catheter into the artery, as required by traditional angiography.
Magnetic resonance imaging( MRI) with functional probes
Functional magnetic resonance imaging( MRI) enables researchers to evaluate the activity and activity of nerve cells in various areas of the brain. Functional magnetic resonance imaging( MRI) estimates areas of the brain that control movement, speech, vision, memory.