Magnetic Resonance Imaging

What is MRI?

  • MRI, or magnetic resonance imaging, is an advanced medical imaging procedure that allows us to create extremely detailed and precise pictures. We can look at these snapshots of the inside of your body from almost any perspective -- either as a whole structure, or as a single slice of a body part. With these views, we look for what belongs and what does not belong in the picture. Radiologists have a mental catalogue of what "normal" looks like, and our job is to pick out what shouldn't be there. Neuroradiologists are radiologists who work in the area of brain and spine imaging, for which MRI is ideally suited.

    Unlike the CT scanner that uses x-rays, the MRI uses electromagnetism and radio waves. In fact, the MR scanner is, at heart, a very powerful magnet. That explains the word "magnetic" in the name MRI. Radio waves are used to listen to the almost imperceptible effects of the magnetism, and computers are used to convert the radio signals into images.

    MRI is not only for the brain and spine; it can also be used to study other parts of the body, such as the shoulder and knee joints, the heart, and even the unborn child during pregnancy. New applications of MRI are developed every year, and in many circumstances, MRI provides information that cannot be obtained with other radiological techniques.

Is the procedure safe?

  • MRI is a very safe procedure. As noted above, MRI does not use x-rays. In theory, you could undergo many MRI examinations without any cumulative effects.

Who should not be examined with MRI?

  • Because of the powerful magnetic field, MR imaging is particularly sensitive to metal. The MR scanner can cause pieces of metal, like some of the older aneurysm clips, to move. Itcan also cause some medical devices, like pacemakers, to malfunction. Metal can also degrade the quality of MRIs so much that the images are unreadable, such as in some patients with metal hardware from prior spine surgery. For these reasons, MRI is generally not performed if you have one of the following:
    • +Cardiac pacemaker* or other implanted electronic devices
    • +Certain types of cerebral aneurysm clips
    • +Certain types of metallic implants
    • +Metal fragments in the eyes
    * Recently, some MRI safe pacemakers have been introduced, but for now, the vast majority of these devices are not safe.

    MRI technologists are trained to ask you a series of questions to determine whether you can safely undergo an MRI study. For your safety, they are trained not only to ask these questions, but to ask the questions several times with slightly different wording. You should anticipate being asked the same type of question several times. When a metal fragment may be present in your body, either x-ray or CT may need to be obtained before you can be allowed to enter the MRI unit safely. Therefore, it is very important to notify the MRI technologist if you think you may have metal objects in your body. Some metal objects are, however, perfectly safe for MRI. After considering the information obtained by the technologist, the radiologist will make a decision about whether it is safe to proceed with your MR exam.

Can pregnant women undergo an MRI examination?

  • After years of study, there is no evidence to suggest that MRI is harmful to either a pregnant woman or her fetus. In fact, MRI is often performed in pregnant women to examine the fetus. However, to minimize the risks, many imaging centers prefer that pregnant patients undergo MRI only if they have a serious or life-threatening illness. Occasionally, ultrasound examinations of the fetus reveal abnormalities. In some of these cases, MRI is ordered to study the fetus in greater detail.

Is special preparation needed for the study?

  • In general, no special preparation is needed. You can eat and drink normally and take any regular medication prior to the study. However, some children may need to be sedated before entering the MRI machine to prevent them from moving too much during the study. These children will need to fast for a few hours before receiving the sedatives.

What occurs on the day of the study?

  • When you arrive for an MRI examination, you are typically asked to remove all personal items such as watches, wallets, and car keys. Most MRI facilities provide secure lockers where you can store items during the procedure. You are generally asked to change from street clothes into a hospital gown, to ensure that no metal clips, buckles or skin ornaments are touching the skin, as there have been uncommon cases of skin burns.

What happens during the MRI?

  • As you enter the MRI suite, you will see the large magnet and patient table at the center of the room. Typically, you will lie on your back and depending on which body part is being examined, you will enter the scanner either head first or feet first. If we are studying your brain, you will be asked to slide your head into a head coil, much like a helmet. When acquiring images, the MR scanner tends to be fairly loud, making a series of buzzing and knocking noises. Typically, the MR technologist will offer earplugs or headsets if you wish to listen to music.

    Each set of images takes several minutes to acquire. It is important that you remain as still as possible as motion will blur the images, potentially making them un-readable.

    You will be able to communicate with the technologist via an intercom system. The technologist will be speaking with you during various stages of the examination to explain what will happen at each step of the way.

Does a needle need to be placed for this procedure?

  • In some cases, an MRI contrast agent is injected through a vein to help the radiologist some things that might otherwise not show up on the images. This contrast material is extremely safe, and its incidence of side effects is very low. That said, the MR technologist is focused on your safety: he or she will be asking questions to ensure you do not have any side effects.

Can claustrophobic patients undergo MRI?

  • Some patients may feel claustrophobic in the MR scanner. This used to be more of a problem than it is today, as newer MR scanners are much shorter than their older counterparts. Patients who are claustrophobic can be sedated to reduce their anxiety prior to and during the examination.

    Alternatively, some MRI centers have "open" magnets that offer more space and a better view around them. In general, these magnets are less powerful than conventional ones, and they produce images that show slightly less detail.

Are there any special instructions for patients after their MRI?

  • None. You will be able to resume your normal daily activities immediately after the procedure.

Who will interpret my MRI?

  • As noted above, in general, a radiologist will interpret your scan. Radiologists have completed four years of training, and often additional, specialty training in interpreting x-rays, ultrasound, and CT and MR scans. The results of your scan will be available to your personal physician typically within the same or next day.