MRI head is a non-invasive study that allows visualizing bones, soft tissues and intracranial structures by registering radiomagnetic pulses of hydrogen atom nuclei placed in an external magnetic field. Head MRI is used to study the brain and its membranes, pituitary gland, intracranial vessels, ENT organs, paranasal sinuses, orbital zone and superficially located soft tissues of the head. It is used in neurology, neurosurgery, oncology, ophthalmology, otolaryngology, maxillofacial surgery and other fields of medicine.
MRI head was invented in the 70s of the last century, began to be introduced into clinical practice in the 80s of the last century, became available to Russians about 20 years ago. The use of this technology has significantly increased the level of diagnosis in diseases and head injuries. MRI head made it possible to simplify the process of examining patients, turned the ideas about the level of informativeness of non-invasive studies and greatly expanded the capabilities of specialists in identifying a number of pathological conditions.
Comparison of CT and MRI
CT and MRI head have recently been included in the list of routine diagnostic studies used for developmental anomalies, volume formations, inflammatory diseases, injuries, acute and chronic disorders of cerebral circulation. Both techniques make it possible to obtain a three-dimensional image of the area under study, to enlarge individual sections of this image, to study various structures in layers and in different projections.
However, there are certain differences between CT and MRI head. CT is a method of radiation diagnosis. In the course of the study, X-rays are used, which pass through the patient’s body. Special sensors located on the other side of the body record the received information and transmit it to the computer for further processing. There is no radiation load during MRI head. The data is obtained by recording electromagnetic vibrations emitted by atomic nuclei in an external magnetic field. Due to the absence of X-ray radiation, MRI head with minor limitations can be used in the process of diagnostic search in children, pregnant women and persons who have previously received a significant dose of radiation (with multiple radiographs, radiation therapy).
CT head allows you to get detailed information about the state of solid structures (bones of the cerebral and facial skull). On the MRI head, bone structures are displayed in the form of black shadows, which limits the use of the technique in detecting fractures. At the same time, MRI head makes it possible to determine the areas of intracerebral hemorrhages even before they become visible during CT, therefore, it is successfully used in the early diagnosis of strokes and other urgent conditions caused by traumatic brain injuries and disorders of cerebral circulation.
The price of an MRI head is higher than the cost of a CT scan. In the regions, the technique may be less accessible due to the lack of necessary equipment, especially in small settlements. The study is contraindicated in the presence of installed paramagnetic objects (metal structures, electronic devices). Despite all these disadvantages, head MRI is a highly informative method of research and in some cases allows you to make a diagnosis with questionable results of other diagnostic procedures, including head CT.
Types of research
Taking into account the studied areas , the following types of head MRI are distinguished:
- MRI of the brain
- Pituitary MRI
- MRI of brain vessels
- MRI of the paranasal sinuses
- MRI of the eye orbits and optic nerves
- MRI of ENT organs
- MRI of the inner ear.
MRI head is performed with or without the use of a contrast agent. To increase the information content, T1- and T2-weighted images are used (images formed during periods of time when a certain number of protons returns to the equilibrium state and shifts in phase). MRI head using contrast – paramagnetic gadolinium metal allows you to get clearer T1-weighted images.
MRI head is a technique used at the final stages of diagnostic search, after skull radiography, echo-encephalography, CT of the brain and other diagnostic procedures. In the event of some acute conditions, an MRI head can be used as an emergency, with a minimum number of preliminary studies. The purpose of the planned procedure is to clarify the data obtained by using other diagnostic methods. MRI head is used to make a final diagnosis, prepare a plan of conservative therapeutic measures, decide on the expediency of surgical intervention, monitor the condition of the pathological focus during treatment and detect relapses in the long term.
MRI brain is prescribed to study intracerebral structures, detect pathological foci, determine their shape, size and exact localization, as well as to assess capillary blood flow, obtain information about the state of various functional zones, the concentration of certain metabolic products and the pH of brain tissues. MRI head is carried out in an emergency or planned manner. An emergency procedure is used for TBI and acute disorders of cerebral circulation. Planned MRI head is used in the diagnosis of abnormalities of brain development, inflammatory processes, bulky formations, arteriovenous malformations and demyelinating diseases. MRI head is also prescribed to assess the state of the cerebrospinal fluid system and to track the results of treatment after strokes, traumatic injuries and surgical interventions on the brain.
MRI of the pituitary gland allows you to assess the condition of the pituitary gland and the Turkish saddle, identify volumetric pathological processes, determine their shape, size, localization and prevalence, and carry out accurate differential diagnosis. This type of head MRI is prescribed for suspected cancer, prolactin and pituitary adenoma. The procedure makes it possible to diagnose microadenomas smaller than 10 mm, which are extremely difficult to detect using other research methods. To increase the information content, MRI head is usually performed using a contrast agent.
MRI of cerebral vessels is used to obtain information about the state of intracerebral vessels and create three-dimensional models of vascular networks. MRI head allows you to determine the condition of blood vessels and surrounding tissues, assess the degree of damage to the vascular bed, specify the localization and prevalence of pathological processes caused by circulatory disorders. This type of head MRI is prescribed for suspected intracranial hematoma, acute hemorrhagic and ischemic stroke, chronic cerebral circulatory disorders of various genesis (post-traumatic, post-stroke, due to encephalopathy, etc.), cerebral arachnoiditis, Parkinson’s disease, vegetative-vascular disorders. MRI head is also used at the stage of planning surgery and to evaluate the results of treatment.
MRI of the paranasal sinuses is used to assess the condition of the paranasal sinuses, identify local pathological foci and common processes. MRI head is prescribed in case of diagnostic difficulties after radiography and CT paranasal sinuses, if there is a suspicion of volumetric formations and sinusitis complicated by an orbital or cranial abscess. In the presence of volumetric processes, contrast agents are used.
Head MRI is contraindicated in the presence of any paramagnetic implants, including pacemakers, vascular clips, metal plates and Ilizarov devices. The exception is titanium metal structures that do not have ferromagnetic properties. Patients with titanium implants must submit to a specialist documents confirming the composition of the metal structure and evidence of the safety of MRI. Tattoos applied with the use of metal-containing dyes are also considered as a contraindication.
High-quality visualization of the structures of the head is possible only while maintaining complete immobility, therefore, the list of relative contraindications to MRI head includes age younger than 5 years, motor anxiety of various origins, severe pain syndrome, drug or alcohol intoxication and mental illnesses that prevent the implementation of doctor’s instructions. If necessary, medical sleep, sedatives and painkillers are used for the study.
Native and contrast MRI are not used with a body weight over 120-130 kg and other established limitations for equipment. Native MRI is not prescribed in the first half of pregnancy (except in cases when the study is necessary for vital reasons), MRI head with contrast – during the entire gestation period. In addition, the use of contrast is contraindicated in the presence of an allergic reaction to the contrast agent and in chronic renal failure. The lactation period is not a contraindication to MRI head. After the end of the study, patients should refrain from feeding for two days, since the contrast agent is excreted in breast milk.
Preparation for MRI
Special training is usually not required. The patient can take food and medications as usual. Before an MRI head with contrast, patients suffering from kidney diseases should take a general urine test and blood biochemistry. The doctor must submit all available medical documentation (extracts, conclusions of consulting doctors, CT results, radiography and other studies), report the presence of pregnancy, claustrophobia, allergic reactions and installed metal implants. On the day of the head MRI, patients are advised not to wear jewelry and not to take valuable metal products with them, since all metal objects will need to be left in another room to avoid their negative impact on the quality of the images.
Methodology of conducting
Before starting an MRI of the patient’s head, they are asked to take off watches, jewelry, hairpins, dentures, hearing aids and clothes with metal parts and put on a hospital shirt (in the absence of metal parts in clothes, some clinics are allowed not to change clothes). The patient is placed on a table, with a contrast MRI head, a contrast agent is injected and the table is moved inside the tunnel of the tomograph. During the examination, the patient can inform the doctor about the presence of unpleasant sensations using the built-in microphone. After the procedure is completed, the specialist examines the data obtained, prepares a conclusion and transmits it to the patient or the attending physician.