Magnetic resonance imaging (MRI) is a safe and painless test that uses sound waves and a magnetic field to produce clear cross-sectional or three-dimensional images of the body’s tissues. Unlike an x-ray or a computed axial tomography (CAT) scan, MRI uses no radiation.
MRI may be administered with or without the use of a dye, known as a contrast medium. The contrast medium helps increase the visibility of organs and tissues for a more detailed image. If a contrast medium is used, it is typically injected into the patient’s vein prior to the test.
Because of its safety and clarity, the MRI is a valuable tool that can aid in the diagnosis of a wide range of conditions, including:
Cancer
Musculoskeletal (bones and muscles) disorders
Heart and vascular disease
Brain abnormalities (aneurysm, stroke)
Disorders of organs (lungs, liver, kidneys)
MRI can be helpful in diagnosing cancers of the male and female reproductive systems (e.g., ovary, prostate, endometrium) and to diagnose breast disorders, such as breast cancer or a rupture in a breast implant.
Because the MRI test relies on a large magnetic field, certain people should avoid the test. Pregnant women should generally avoid MRI because the risk to the developing fetus is unknown. Experts advise pregnant women not to have an MRI during the first trimester (12 weeks) of their pregnancy. In some cases, alternative imaging methods such as ultrasound can be used. However, there may be some instances when an MRI is warranted in pregnant women and the patient's physician will determine its necessity.
In addition, patients with implanted pacemakers and implantable cardioverter defibrillators (ICDs) should avoid the test. Patients with certain other medical implants, such as metal plates or heart valve replacements, should consult with their physician regarding the restrictions of the test. Women with intrauterine devices (IUDs) can safely have an MRI. In all cases, patients should inform the physician or technician of any metal objects present in their bodies.
An MRI scan may take up to one hour to complete in a rather tight space. Patients who become nervous or anxious in small spaces may wish to ask their physician about receiving a sedative prior to the MRI. Using a less enclosed type of MRI machine, known as an open MRI, may be another option. If patients receive a sedative, they may be unable to drive following the test. Otherwise, patients are able to resume their daily activities after the MRI is completed.
About magnetic resonance imaging
The magnetic resonance imaging (MRI) test uses a powerful magnetic field to create images of structures and organs within the body. It is a safe and usually noninvasive test that can help physicians diagnose a wide range of diseases and conditions without subjecting the patient to radiation.
An MRI works by placing the patient in a chamber surrounded by a magnetic field. The center (nucleus) of atoms in the patient’s body responds to the magnetic force in characteristic ways, allowing a computer to produce clear cross-sectional or three-dimensional images.
Sometimes MRI involves the use of a contrast medium that increases the clarity of the images by making the body’s tissues more responsive to the machine’s magnetic and radio waves. Contrast medium is typically provided through intravenous injection but in some cases, it may be swallowed in liquid form. If no contrast medium is used, the patient may complete the test without any needles.
MRI is often used to diagnose the following:
Detection and staging of various forms of cancer
Strokes and chronic disorders of the nervous system
Brain abnormalities in patients with dementia
Diseases of the pituitary gland
Eye or inner-ear tissue abnormalities
Damage from heart attack or heart disease, including vessel plaque and blockage
Bone and joint damage, infections, injuries or degenerative disorders
Functional disorders of internal organs
Reproductive system and bladder problems
Conditions that affect women and can be diagnosed using MRI include:
Disorders of the pelvis, hips and bladder. MRI frequently is the preferred imaging technique when diagnosing conditions in these areas of the body in both women and men. Unlike other imaging systems, such as computed axial tomography (CAT scan), MRI allows the physician to view an area of the body in multiple planes. This is especially valuable in imaging pelvic structures that are not clearly viewed.
MRI also does not use radiation, which is an advantage when examining reproductive organs that are vulnerable to potential damage from radiation.
Several studies have shown that MRI is an effective technique for diagnosing reproductive cancers such as those of the endometrium, ovaries and cervix.
Breast disorders. Clinical trials are under way to determine the effectiveness of using MRI as a screening tool for breast cancer. An MRI can produce side-to-side, top-to-bottom and front-to-back images of the breast without exposing the patient to radiation. However, MRI cannot always distinguish between conditions that are malignant (cancerous) and those that are benign (noncancerous). In addition, MRI cannot detect microcalcifications in the breast. A mammogram continues to be the optimal imaging test for detecting the first signs of breast cancer.
Special MRI machines are currently available in some medical centers that are designed for breast examinations. Research studies have shown that enhanced MRI may be an effective tool for early detection of breast cancer. It is becoming increasingly popular as an addition to mammography, particularly with high-risk women, such as those with a genetic link to breast cancer.
MRI is also used to evaluate breast implants for possible leaks and ruptures and screen for abnormalities in dense breast tissue, which is often found in younger women.
Before magnetic resonance imaging
Typically, magnetic resonance imaging (MRI) is an outpatient procedure performed at a hospital or clinic. Patients should closely follow their physician’s recommendations when preparing for the test. Normally, patients will be allowed to eat without restriction and to take their usual medications. Once at the facility, patients may be asked to change into a gown or to wear clothing without fasteners, such as a sweatshirt and sweatpants. Women may need to remove their bras due to underwires or metal hooks.
It is important for the patient to remove all personal metal objects (e.g., rings, earrings, necklaces) before the test. In fact, patients may want to leave these objects at home on the day of the test. There should be no metal objects inside the room in which the MRI is being performed.
Certain types of implanted medical devices rule out the use of MRI. These objects generally include (but are not limited to):
Pacemakers
Implantable cardioverter defibrillators (ICDs)
Artificial hips, knees and other joints (in some cases)
Inner ear (cochlear) implants
Titanium implants in the mouth
Aneurysm clip of the brain
Neuromuscular stimulators
Implanted drug infusion pump, such as an insulin pump
MRI may be allowed with other types of medical devices, such as artificial joints and certain types of stents and heart valves. In some cases, a specified period of time must have elapsed between the implant of the device and MRI. Patients with these devices should inform their physician and obtain approval before scheduling an MRI. If patients even suspect that they have a metal device or fragment (such as from an injury) inside their body, an MRI might not be an option. Women with intrauterine devices (IUDs) can safely undergo an MRI procedure.
Some MRIs require the use of a contrast medium (dye). In most cases, it is injected into a vein in the arm or hand shortly before the procedure. For some conditions, it may be swallowed in liquid form. This dye can increase the clarity of the images by making the body’s tissues more responsive to the machine’s magnetic and radio waves. In many cases, MRI is first completed without the dye and a second scan is taken following the dye injection. The patient’s physician will order the appropriate test (e.g., with or without contrast) depending on the condition.
During and after magnetic resonance imaging
The magnetic resonance imaging (MRI) chamber is a relatively tight space, and individuals undergoing a scan may be required to lie still for an hour or more, sometimes as long as two hours. Some people may feel uncomfortable or claustrophobic in this environment. In many machines, music can be played via speakers or headphones to help patients relax. Individuals who become anxious in small spaces may want to discuss with their physician the use of a sedative prior to the procedure. Newer “open” MRI scanners have been designed to increase patients’ comfort levels, but they are subject to more background interference in the images they produce.
The patient is placed on a long bed that slides into the MRI chamber. The technician usually administers the MRI from a control room or small area separate from the scanner. However, the technician and the patient are able to communicate during the test through an intercom system. This allows the technician to provide instructions and the patient to express any concerns. Some patients may be given a hand-held buzzer to stop the test in case of some type of emergency.
Once inside the chamber, the patient should relax and lie still for the duration of the procedure. Patients may be instructed to hold their breath at times or may be removed from the scanner for repositioning.
The MRI equipment will make many different types of noises during the scan. These may include loud thumping or buzzing sounds as the machine takes multiple views of the targeted site. These noises are a normal part of the MRI procedure. A nurse or technician periodically checks with the patient during the scan.
Those taking the test should be able to leave immediately following the MRI with no side effects. Patients who have received a sedative may need someone to drive them home after the test.
Results of the test are recorded on a series of films. The films are reviewed by a radiologist and a complete report will be written by the examining radiologist. A copy of the report is sent to the patient’s physician to help confirm a diagnosis or prescribe further tests and treatments.
Some physicians may request that patients bring their MRI films with them to a follow-up appointment. Individuals should check with the facility to determine the correct procedure for obtaining their films prior to their appointment.
Potential risks with MRI
Pregnant women should avoid having magnetic resonance imaging (MRI) unless absolutely necessary, because risk to the developing fetus is unknown. Experts especially urge pregnant women not to have an MRI during the first trimester (12 weeks) of their pregnancy. As a result, ultrasound (which uses sound waves to create an image) is more likely to be used to create images for women in the first trimester of pregnancy.
Women who are breastfeeding should consult a physician or radiologist about whether it is appropriate to undergo an MRI. In some cases, a woman may pump breast milk before the procedure and refrain from breastfeeding until the contrast material has cleared her body. The radiologist or technician will be able to provide information as to when it is safe to resume breastfeeding following an MRI that uses a contrast medium.
Patients with tattoos or permanent makeup are encouraged to consult with their physician before an MRI is performed. These patients might feel some mild discomfort or a burning feeling on their skin due to a reaction between iron oxide or other metallic substances commonly found in the darker inks of the tattoo and the magnetic field generated during the test. Furthermore, large or very dark tattoos can also cause “artifacts,” or false shadows to appear on the film produced from the test.
If the MRI involves injection of a contrast medium, there is the possibility of a reaction. Patients should inform their physician and the technician if they have an allergic reaction to shellfish. The contrast medium contains iodine, the same element found in many types of shellfish. Patients with an allergic reaction may experience nausea, headache or pain at the site of injection. In severe cases, the patient may develop an anaphalactic reaction with swelling in the mucous membranes, such as in the throat, resulting in the inability to breathe.
Ongoing research regarding MRI
There are a number of studies being conducted in the area of MRI. Research has focused on advanced MRI technology for the diagnosis and treatment of several medical conditions. Current research studies include the following areas:
New imaging systems. The 7 Tesla MRI system is being tested in several research medical institutions in the United States. This scanning system utilizes stronger magnetic fields that show promise for higher sensitivity, speed and resolution.
Contrast agents. Scientists continue to research the development of new contrast agents that can improve MRI. Some studies are examining the use of several contrast agents together, known as combined contrast enhanced MRI. The combined agents have been accurate in detecting liver fibrosis and liver cancers. In addition, advances with contrast-enhanced imaging has improved techniques for MRI-guided biopsies.
MRI with heart implants. Researchers are developing methods that may allow patients with certain heart implants to undergo MRI testing. The method involves reprogramming the devices and using a lower-energy scan. It has been tested with modern implanted defibrillators and pacemakers. The U.S. Food and Drug Administration (FDA) has not authorized any implanted cardiac device for MRI testing, except in research studies.
New computer analysis. Several researchers and technology companies have focused on developing new software programs for MRI testing. New software has shown promise for early detection and treatment of breast cancer using serial-time images.
Treatment for uterine fibroids. Researchers are examining the effectiveness of MRI technology for the treatment of fibroids in the uterus. In this procedure, MRI images are used to help a physician utilize a technique called focused ultrasound heating that destroys the fibroids. This treatment method is also being applied to tumors of the breast.
Questions for your doctor regarding MRI
Preparing questions in advance can help patients have more meaningful discussions with their physicians regarding their conditions. Patients may wish to ask their doctor or healthcare professional the following questions about MRI:
What do you hope to learn from my MRI?
Why should I have an MRI instead of another imaging procedure?
Where can I go to have my MRI done?
How long will it take to complete?
Will my MRI be done with or without dye?
What are the chances I will have a reaction to the dye?
How will I know I’m having an allergic reaction?
Can I have my MRI done in an open MRI machine?
Should I have a sedative before the test to avoid anxiety?
When will I receive the results of my MRI and by whom?
How often will I need an MRI for my condition?
What test can be substituted if I can’t have an MRI?
