Magnetic resonance imaging: know the exam and how it is done

To better visualize the internal organs, it is necessary to make use of some instruments. Among the tests that allow the evaluation of these structures is magnetic resonance, a type of procedure that uses magnetic waves to generate images.

Understand what this test is, when it should be done and its contraindications to follow!


What is MRI?

Magnetic resonance, or nuclear magnetic resonance, is a non-invasive examination that uses a magnetic field and radio waves to generate detailed images of the organs and tissues of the body.

The magnetic field is the region close to a magnet and that influences other magnets, metallic materials and electric currents.

The resonance machine is capable of generating magnetic fields that, in turn, cause protons to agitate (particles present in the organism that contain an electric charge).

This agitation is captured by the device and transformed into images that reveal the inside of the body.

This makes MRI one of the most accurate diagnostic imaging exams, providing high-definition information of Organs internal organs (more detailed than in other exams) and in 3 dimensions: vertical, horizontal and with the body divided into layers .

Thus, the uses of resonance are numerous. Through it it is possible to identify abnormalities in the brain and spinal cord, view tumors, cysts, breast cancer , lesions and abnormalities in the joints and joints, and many other things.

MRI machine

As we saw earlier, the MRI machine is capable of generating detailed and 3-dimensional images of the internal parts of the body.

The device consists of a large electromagnet, which is, in general, a magnet whose magnetic field (which attracts metals and electrical charges) is formed through an electric current.

In the case of the MRI machine, the electromagnets on the machine must be very large and very powerful.

To create the magnetic field, the device uses a coil in which metal wires are wound and subjected to a high continuous electric current, forming the magnetic field.

During the examination, the electromagnet causes reactions in the body’s protons. Each proton has a magnetic field with positive and negative sides. The electromagnet aligns the protons, leaving them ready to react with radio frequencies, as if they were lined up or ordered.

The moment protons are aligned with the magnetic field, they emit radio frequencies that are captured by the machine, generating the image.

But the device’s technology and structure cause the body’s protons to vibrate at different speeds, forming images in 3 dimensions.

The enclosed and closed structure of the machine has a reason: it is necessary to isolate the capture of waves so that there is no interference in the images formed.

Called the Faraday cage, the structure that surrounds the patient protects his interior from radio waves, static and even lightning.

All these details make the machine very expensive and cost up to 3 million dollars. For this reason, the price of exams done on this machine tend to be more expensive than the others.

How does the MRI scan work?

Most of the human body is made up of water molecules, which in turn are made up of hydrogen and oxygen atoms. At the center of each hydrogen atom is an even smaller particle called a proton.

Protons are like tiny magnets with positive and negative poles. When a patient performs an MRI scan, the magnetic field generated by the machine causes the protons to line up in one direction, ready to react with the radio waves.

With the protons aligned, the radio waves are directed to a specific part of the body to be examined causing the protons to vibrate. This vibration is captured by the receivers in the machine, making it know the exact location of the protons in the body, making it possible to distinguish between different types of tissue.

As the protons of the tissues realign themselves at variable speeds, they end up producing different signals, which, in turn, are translated into detailed images of the interior of the human body.

It works like this: in the same way that millions of pixels in a computer can create complex figures, the signals emitted by the millions of protons in the body are combined, creating images.

What is it for?

We can say that the main function of the exam is to generate images of the internal parts of the body. It is through this capability that the MRI machine is able to fulfill the following purposes:

  • Identify abnormalities in the brain and spinal cord;
  • Visualize tumors, cysts and other conditions in different areas of the body;
  • Assist in the diagnosis of breast cancer;
  • Generate images of injuries and abnormalities in joints and joints, such as those of the back, knees, shoulders, etc;
  • Assist in the diagnosis of cardiovascular diseases;
  • Visualize changes in the liver and other abdominal organs;
  • Visualize blood vessels (arteries and veins);
  • Assess the urinary system (kidneys, bladder, prostate);
  • Assist in the evaluation of pelvic pain in women, helping to diagnose diseases such as fibrosis and endometriosis;
  • Assess suspicion of abnormalities in the uterus and risks of infertility.

These are just some of the uses of the MRI scan, it is still possible to diagnose many other problems, such as brain tumor, multiple sclerosis and autoimmune diseases .

How is done?

Magnetic resonance imaging, as the name implies, uses a magnetic field to generate images. As a consequence, during the examination, it is necessary for the patient to remove all metal objects from the body.

That is, hair clips, watches, glasses, bra with rims, wigs, hearing aids, rings, earrings, necklaces and other accessories must be removed. This must be done not only because the presence of the metal can affect the images, but also because of the strong magnetic field generated by the machine, which can suck the object, even causing injuries to the patient.

The MRI machine is like a giant magnet. Therefore, some metal object poorly handled by the patient can be sucked into the machine, damage it and even hurt the patient.

Even though small, these elements gain a lot of strength when they are pulled into the machine, causing simple coins to cause serious injuries.

After removing all metals, the patient must enter the machine. The MRI machine is shaped like a giant donut. During the test, the patient lies on a movable table that slides into the opening of the machine.

A technician supervises the entire procedure in another room. Once the patient is positioned, the examination begins.

During the procedure, the internal part of the machine, the magnet itself, produces repetitive beats that may seem frightening to some patients, but are actually only indications that the machine is working correctly.

The device also has a microphone through which it is possible for the responsible professional and the patient to talk during its execution.

In the case of people who suffer from claustrophobia, the fear of staying in tight and closed places, there is the option of medicating the patient beforehand to help decrease anxiety levels .

Read more: How to control anxiety? 14 tips to avoid crises

When the noise made by the machine is too loud, professionals can provide earplugs or headphones with music to help block out the noise.

The patient does not always need to enter the tube completely. If the injury happens to the foot, for example, it is possible that the upper body remains outside the machine, which reduces anxiety and discomfort.

It is also worth mentioning that, despite the long duration (sometimes the exam can take 1 hour or more), there are pauses.

The images are usually taken in series and the professional warns the patient when he must remain immobile, giving the patient time to scratch his nose, move his foot and other similar movements.


Magnetic resonance devices can have different technical characteristics, magnetic field, device dimensions and image capture, transmission and processing capabilities.

This means that there are different types of MRI depending on the objective and the organ to be analyzed. Understand:

Magnetic resonance imaging of the skull

MRI is most commonly used in the brain and spinal cord, the most elongated portion of the nervous system.

In this modality, the exam is intended to diagnose brain vessel aneurysms, disorders of the eye and inner ear, multiple sclerosis, spinal cord injuries, stroke, tumors and traumatic brain injuries.

Magnetic resonance imaging of the pelvis

One of the uses of magnetic resonance imaging is in the pelvis region. It allows the evaluation of the organs that are located in the lower abdomen, the bottom of the belly.

In this way, it is possible to study the bladder, the uterus, the ovaries, the prostate and the seminal vesicles.

This exam is usually performed in conjunction with an abdominal MRI, which is referred to as abdominal-pelvic magnetic resonance imaging .

Spine MRI

Magnetic resonance imaging can also be done on the spine. It is one of the best methods to diagnose pathologies such as herniated discs (or herniated discs), spondylosis ( spinal arthrosis ), vertebral slips, spinal stenosis (spinal tightness) and several other conditions.

Thus, the exam can be subdivided into four categories, each with a greater emphasis on the spine regions:

  • Cervical spine MRI: close to the neck;
  • Dorsal spine MRI: region close to the chest;
  • Lumbar spine MRI: part close to the navel;
  • Lumbosacral spine MRI: final part of the spine.

Magnetic resonance imaging of the heart and blood vessels

This MRI modality seeks to assess the size and function of the cardiac cavities, the thickness and movement of the heart walls, the extent of damage caused by a heart attack or other cardiovascular disease , blockages in blood vessels and aneurysms.

Magnetic resonance imaging of internal organs

Magnetic resonance imaging of internal organs seeks to detect tumors and other abnormalities in various organs, such as the liver, kidneys, spleen, pancreas, uterus, ovaries and prostate.

Magnetic resonance imaging of the knee, bones and joints

This modality helps doctors to assess joints and identify abnormalities caused by injuries, such as damaged cartilage and ligaments.

Another objective is to verify the presence of changes in the spinal discs, bone infections and tumors in the bones or soft tissues.

Magnetic resonance imaging of the breast

MRI of the breast is more specific. It is usually used in conjunction with mammography to detect breast cancer when the disease is suspected.

Open MRI

In the case of patients who are really claustrophobic and are unable to enter the machine, there is the option to do the “open” MRI.

The open machine, instead of being threaded, has a “U” shape, however, it can be as narrow as the normal machine.

Compared to the traditional method, there may be a reduction in the quality of the images, but depending on the types of symptoms to be analyzed, it may be more useful.

For example, a patient may experience pain in his back , but that pain does not feel when he is lying down. The open machine allows you to analyze this pain and its consequences with the patient inclined, providing more realistic data about the condition.

Contrast magnetic resonance imaging

Contrast is a liquid that enhances the quality of images in the organs and blood vessels, making it easier to transcribe and form the results.

MRI contrast is used when doctors are looking for more data and more details about the state of health, size, and composition of body tissue to be analyzed during the exam.

The need to use the product usually varies according to the location to be examined and the specific pathology that is investigated.

Unlike computed tomography, which uses iodine as a contrast material, contrast-enhanced MRI uses gadolinium, another chemical compound that will help the equipment generate images.

This medication is injected through an intravenous access route in the patient during the entire exam, increasing the accuracy of the final diagnosis.

How long does the MRI last?

The duration of the MRI will depend a lot on the type of exam being performed, the condition being observed and the purpose of the investigation.

In general, the duration of the exam can vary from 30 minutes to 2 hours. Depending on the purpose of the exam, the patient can even watch movies, smell, hear sounds, perform cognitive tasks (such as doing head calculations), pressing buttons and other things.

To find out exactly how long your exam is, talk to your doctor so that he can explain the whole procedure to you.

What are the advantages and disadvantages?

When compared to other tests, magnetic resonance imaging has some advantages and some disadvantages. Understand:


MRI machines do not use ionizing radiation, which can be considered an advantage by some people due to the possible effects of the substance.

Another differential of MRI is the ability to generate images in any dimension (vertical, horizontal and longitudinal). While the tomography is limited to a single plane, the MRI machine is much more versatile.


The disadvantages of the exam are restrictions or difficulties, including:

  • People with obesity may have difficulty with the size of the machine (which is not adjustable);
  • Because it is closed, the device can be uncomfortable for patients with claustrophobia;
  • During the exam, the machine is very noisy, which can frighten some people, especially children;
  • It is necessary for the patient to remain completely immobile for a long period (the exam can last from 20 to 90 minutes);
  • People who also have orthopedic equipment, such as pins, plates and joints, cannot perform the examination in the area where these parts are located, as there may be distortion of the images.


For most people, there are no contraindications or health risks in doing MRI. However, there are some situations that can prevent the exam from being performed.

Cases in which the patient has a metallic device that may be influenced by the magnetic field generated by the device, for example, is the most common contraindication.

Therefore, talk to your doctor before taking the exam if you have any of the following devices:

  • Cardiac pacemaker;
  • Implantable cardiac defibrillator;
  • Cochlear implant;
  • Vascular clips of metal;
  • Vascular prosthesis
  • Stent vascular;
  • GOD;
  • Orthopedic prostheses;
  • Metal fragments in the body (such as projectiles of a firearm);
  • Very old tattoos (in the past, inks could contain traces of metals).

It is worth mentioning that not all devices listed above are contraindicated for MRI. There are pacemakers that can be used for resonance, for example.

However, it is very important that you talk to the medical team and inform them of any artificial devices present in the body so that they can decide whether or not the test is safe for you.

Contraindications for contrast-enhanced MRI

There are still contraindications for magnetic resonance imaging performed using contrast. In such cases, the injection of the gadolinium compound is contraindicated for:

  • Patients with severe renal dysfunction;
  • Patients suffering from acute kidney injury;
  • Patients who have undergone liver transplantation;
  • Newborns up to 4 weeks of age.

What are the side effects of the contrast?

Side effects of contrast are uncommon and, when they do occur, tend to be mild, such as itching, irritation, dizziness and vomiting. Elderly, children and people prone to allergies can receive special contrast, with less risk to the reaction.

In general, allergic or side effects occur at the application site, causing itching, redness and pain, but which tend to improve quickly.

Pre-examination and post-examination care

Normally, MRI does not require any prior preparation, however, depending on the type of exam to be performed, the patient may be asked to fast for 3 or 4 hours.

Before the exam, the patient can receive a bathrobe to perform the procedure and must remove any and all metal objects, such as rings, necklaces and jewelry, so that there is no interference in the image.

In the case of people who suffer from claustrophobia, doctors may prescribe a sedative or sedative to calm it down. Except in cases where the patient had to use a sedative, there is not much post-examination care and you can continue with your daily activities as normal.

When the test was done using contrast, it is necessary to drink plenty of water to help eliminate the liquid naturally.

As for the people who needed to be sedated during, there are some precautions and they involve:

  • Do not drive or use public transport for at least 24 hours;
  • Do not operate machinery for at least 1 day after the exam.

What can affect the results?

When the results of an MRI are affected, this is usually due to some change in the formation of the image.

The main reason for these changes is to perform the exam with some unnoticed metal. For example, people who have orthopedic plates and screws may have their exam images altered if the prosthesis is too close to the site to be examined.

During the procedure, it is also necessary for the patient to remain immobile. If the patient moves too much, the images may not be clear.


Magnetic resonance imaging is painless and safe. Some people may feel uncomfortable during the performance, especially if they have claustrophobia, which can generate a severe degree of anxiety.

Although there is no study proving that the MRI scan causes any harm to the human body, certain patients should avoid taking the scan without first talking to the doctor and measuring the risks and benefits.

Price: what is the value of an MRI?

The price of MRI varies a lot according to the complexity of the exam, the duration and the area to be visualized. However, on average, the value is between R $ 800 and R $ 1,000.

Common questions

Can pregnant woman do MRI?

It depends. Pregnant women are allowed to perform the exam as long as there is an indication and need, because, despite not having ionizing radiation (which harms the pregnant woman and the baby), it is better to avoid exposure to magnetic waves for at least the first three months of pregnancy. gestation.

For this reason, always talk to your doctor before taking any exam. The effects of magnetic fields on the human body are not yet fully understood and the doctor may recommend an alternative test that offers less risk.

Does MRI hurt?

No. Magnetic resonance imaging is a painless exam. However, discomfort can happen especially when you have a contrast test. In such cases, symptoms such as nausea, vomiting, skin irritation and headache can occur.

Can anyone using an orthodontic appliance do MRI?

Yea! People using orthodontic braces can take the exam as long as their purpose is not to view anything from the neck up, as the metal of the braces can impair image quality.

Who has orthopedic equipment (pins, plates, screws and joints) can do MRI?

Usually, the pins, plates, screws and joints that are implanted in injured patients are made of titanium, which is a metal compatible with magnetic resonance imaging.

However, although there is no risk of injury, it is not possible to assess the location where the orthopedic equipment is, as they can cause distortion of the images.

Magnetic resonance imaging is a simple, safe, painless examination and should be done when the medical team needs to view the internal organs. Have you ever had an MRI scan? How was it? Tell us in the comments!

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