Magnetic Resonance Imaging (MRI)

MRI Machine Semmes Murphy Clinic

Magnetic resonance imaging (MRI) is a diagnostic exam that uses a combination of a magnetic field, radio waves and a computer to create detailed images of the organs and structures within the body.

Most MRI machines are large, tube-shaped magnets. When you lie inside the MRI machine, a magnetic field temporarily realigns hydrogen atoms in your body. Radio waves cause these aligned atoms to produce very faint signals, which are used to create cross-sectional MRI images — like slices in a loaf of bread.

The MRI machine can also be used to produce three-dimensional (3-D) images that may be viewed from many different angles. It does not use radiation.

Why do I need this test?

Magnetic Resonance Imaging is just one of the tools used by Semmes Murphey professionals to diagnose and treat brain, spine, back, or neck problems. In fact, it is the most frequently used imaging test of the brain and spinal cord.

A noninvasive way to produce high-resolution images, it's often performed to help diagnose aneurysms of cerebral vessels, disorders of the eye and inner ear, multiple sclerosis, spinal cord injuries, strokes, tumors and brain injury from trauma.

It also may be used to help evaluate joint abnormalities caused by traumatic or repetitive injuries, disk abnormalities in the spine, bone infections and tumors of the bones and soft tissues as well as joint deterioration resulting from arthritis.

A special type of MRI is the functional MRI of the brain (fMRI). It measures the metabolic changes that occur within the brain and helps assess damage from a head injury or from disorders such as Alzheimer's disease.

Are there any risks?

Radiation is not used in MRI so there is no danger in over-exposure to radiation.

Because MRI uses powerful magnets, the presence of metal in your body may be a safety hazard or affect a portion of the MRI image.

Before having an MRI, tell your doctor and technologist if you have any metal or electronic devices in your body, such as:

  • Metallic joint prostheses
  • Artificial heart valves
  • An implanted heart defibrillator, a pacemaker or another device
  • Metal clips, mesh, plates, etc.
  • Cochlear implants
  • A bullet, shrapnel or any other type of metal fragment

If you have tattoos, ask your doctor whether they might affect your MRI. Some of the darker inks may contain metal.

Please alert your physician if you are or think you may be pregnant before you schedule an MRI. While the effects of magnetic fields on fetuses aren't fully understood, MRI testing during the first trimester is discouraged. Your doctor may recommend choosing an alternative exam or postponing the MRI.

If there is a possibility that you are claustrophobic, your physician may provide an anti-anxiety medication for you to take prior to your MRI examination. If so, you must have someone drive you home after the test.

A doctor may order a contrast medium or dye to be used during the MRI exam, so the radiologist has a better view of internal tissues and blood vessels on the completed images.

The MRI contrast material may affect other conditions, such as allergies, asthma, anemia, hypotension (low blood pressure), kidney disease, and sickle cell disease. There is also a risk for allergic reaction to the contrast. Patients who are allergic or sensitive to contrast dye or iodine should notify the radiologist or technologist.

If you have a history of kidney disease, kidney failure, or are on kidney dialysis, there is a risk of a condition called "nephrogenic systemic fibrosis" from the contrast dye. You should discuss this risk with your doctor prior to the test.

There may be other risks depending on your specific medical condition. Be sure to discuss any concerns with your doctor prior to the procedure.

What should I do to prepare?

Your doctor may have specific instructions related to several issues. But in most cases, there is very little you need to do to prepare for your MRI.

The most important thing you can do to prepare for your test is to alert your physician if you:

  • Are pregnant or might be pregnant,
  • Work with metals or have any metallic particles, bullet wounds, shrapnel or metal plates, pins, staples or devices inside your body,
  • Have any tattoos or permanent eyeliner,
  • Are claustrophobic,
  • Have any type of pacemaker or implanted valves or pumps,
  • Have any type of kidney issues or failures, or
  • Have had any allergic reactions to medications or contrast materials.

A special dye called contrast material is needed for some MRI. Contrast materials can help highlight areas of the body being examined, like blood vessels, intestines or other structures.

  • If your doctor ordered an MRI without contrast, you can eat, drink and take your prescribed medications prior to your exam.
  • If your doctor ordered an MRI with contrast, you need to follow his or her specific instructions.

Please inform your doctor if you have had an allergic reaction to any contrast media. There are medications to help alleviate any reaction. You will likely take this by mouth 24, 12 and two hours prior to examination. These options will be discussed with you in detail when you schedule your exam.

Please discuss all of your medications with your physician. These may be relative to your specific pre- and post-procedure instructions.

If your child, infant or toddler is having an MRI, the doctor may recommend a sedative to keep your child calm and still. Movement blurs the images and may lead to inaccurate results.

The physicians at Semmes Murphey Clinic have a world renown reputation in pediatric surgery and treatment based on their many years’ experience treating patients at both LeBonheur Children’s Hospital and St. Jude Children’s Research Hospital. Your doctor will help you prepare your child for their MRI and any phase of their treatment.

What should I expect during the test?

A radiology technologist, specifically trained and dedicated to administering these procedures, will perform the MRI and guide you through this examination.

Procedures may vary depending on your condition and your doctor's practices, but you can generally expect the following:

You will be asked to remove any, jewelry, eyeglasses, hearing aids, hairpins, removable dental work, or other objects that may interfere with the procedure. You will also be asked to remove your clothes and given a hospital gown to wear.

If you are to have a procedure done with contrast, an intravenous (IV) line will be started in the hand or arm for injection of the contrast dye.

Next you will lie on a motorized table that slides into a large circular opening of the scanning machine.

While the MRI procedure causes no pain, having to lie still for a length of time might cause some discomfort or pain, particularly in the case of a recent injury or invasive procedure such as surgery. The technologist will use a variety of options, like pillows or straps, to make you comfortable and complete the procedure as quickly as possible.

Our goal is to help you relax because it is important for you to remain very still during the examination. Any movement could cause distortion and affect the quality of the scan.

During the procedure, you will be in constant sight of the technologist through a window between the scanner room and the adjacent control room. The technologist will be watching you at all times and using a microphone and speakers inside the scanner to remain in constant communication.

During the procedure, the machine produces a repetitive tapping, thumping or clicking noise. You will be given earplugs or a headset to help block the noise and make you more comfortable.

At times the technologist may ask you to hold your breath for a few seconds, depending on the body part being examined.

A contrast dye may be used to enhance the appearance of certain details. You may feel some effects when the dye is injected into the IV line, like a flushing sensation or a feeling of coldness, a salty or metallic taste in the mouth, a brief headache, itching, or nausea and/or vomiting.

These effects usually last for a few moments. Please notify the technologist if you have any of these feelings.

Once the scan is complete, the table will slide out of the scanner and you will be assisted off the table.

If an IV line was inserted for contrast administration, the line will be removed, and you will be monitored for a period of time for any side effects or reactions to the contrast dye.

If any sedatives were taken for the procedure, you may be required to rest until the sedatives have worn off. You will also need to avoid driving and will need someone to take you home.

You may resume your usual diet and activities, unless your physician advises you differently. There is no special type of care required after an MRI.

Please notify your physician if you have any pain, redness, and/or swelling at the IV site after you return home. This could indicate an infection or other type of reaction.

Your physician may give you additional or alternate instructions after the procedure, depending on your needs.

When will I receive my results?

After the procedure the test results are saved digitally and sent to the radiologist (a doctor who specializes in analyzing these test results and other radiology procedures) who will evaluate the results and send them to your care team.

Your doctor will discuss the results and next steps with you. If your appointment is the same day as your test, your physician may review them with you at that time. Otherwise, most test results are reviewed with you at your next scheduled appointment.

This information was provided by the specialists at Semmes Murphey Clinic. Readers are encouraged to research trustworthy organizations for information. Please talk with your physician for websites and sources that will enhance your knowledge and understanding of this issue and its treatments.

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