Magnetic resonance imaging (MRI) is a safe and painless test that produces clear cross-sectional or three-dimensional images of the body’s tissues, even through bone and other obstructions. Unlike x-rays and computed axial tomography (CAT) tests, which use radiation, MRI relies on radiofrequency sound waves and a magnetic field to produce images of the body.
Because of its safety and clarity, the MRI is a valuable tool that can aid in the diagnosis of a wide range of conditions. There is little preparation necessary for the standard MRI and requires only that the patient remove all metal objects such as jewelry prior to the test.
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 usually injected into the patient’s vein prior to the test. In some cases, the contrast material may be swallowed in a liquid.
MRI is often used to diagnose cancer and to determine the extent of the disease. It is most effective in detecting cancer of the musculoskeletal system, brain and spinal cord and internal organs such as the lungs, liver and kidney. It is a common choice for examining the male and female reproductive systems to detect abnormalities and functional disorders. In addition, physicians are increasingly using MRI to supplement mammography to aid in breast cancer diagnosis.
Because the MRI test relies on a large magnetic field, certain people should avoid the test. These include patients with implanted pacemakers and implantable cardioverter defibrillators (ICDs). Patients with certain other medical implants, such as metal plates or heart valve replacements, should consult their physicians about the restrictions of the test. In all cases, patients should inform the physician or technician of any metal objects present in their bodies. Also, pregnant women should generally avoid MRI because the risk to the developing fetus is unknown. However, there may be some instances when an MRI is warranted in pregnant patients.
The test 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 before the MRI. Using a less enclosed type of MRI machine, such as an open MRI, may be another option. If patients receive sedatives, they may be unable to drive home following the test. Otherwise, patients are free to go about their daily activities after the MRI is completed.
About MRI & cancer
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. If a contrast medium (dye) is not used, the test can be completed without the use of needles.
An MRI works by placing the patient in a chamber surrounded by a magnetic field. The centers (nuclei) of atoms in the patient’s body responds to the magnetic force in characteristic ways. THe procedure allows a computer to produce clear cross-sectional or three-dimensional images of tissues and organs in the body.
MRI can be used to help detect several types of cancer, particularly those that are present in the central nervous system and the spine, such as cancers of the brain, spinal cord, and head and neck. Research has also found that MRIs may detect very early stages of breast cancer that may be missed by standard mammography. In addition, MRI may provide better images in women with dense breast tissue.
MRIs can also be used to determine the extent of cancer growth and how far it has spread, a system known as cancer staging. However, unlike CAT scans and x-rays, MRI does not reveal calcifications, which are tiny mineral deposits that often suggest cancer.
MRI may be 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 caused by heart attack or heart disease
- Blood vessel plaques and blockages
- Bone and joint damage, infections, injuries or degenerative disorders
- Functional disorders of organs such as the lungs, liver, pancreas, kidney and spleen
- Reproductive system and bladder problems
Sometimes MRI involves the use of a contrast medium (dye) to make the body’s tissues more responsive to the magnetic waves. The dye can highlight tissues and organs, increasing the clarity of the images. Contrast medium is typically provided through intravenous injection, but in some cases, it may be swallowed in liquid form.
Cancers diagnosed with MRI
There are many types of cancer that can be either detected or staged using magnetic resonance imaging (MRI). In some cases, images provide enough detail that physicians can distinguish a noncancerous (benign) tumor from a cancerous (malignant) tumor. However, a tissue biopsy is still necessary to definitively diagnose cancer.
MRIs can be used for detection and staging of the following cancers:
- Brain cancer. When used with contrast agents injected into a vein in the arm, an MRI is the most effective way to detect tumors in the brain.
- Bone cancer. MRI is effective at detecting the spread of cancer from the bones into nearby muscles, fat and tissues.
- Pituitary gland cancer. MRI is recognized as the best imaging technique for detecting pituitary tumors of all types. It can identify macroadenomas (large pituitary adenomas) and microadenomas (small pituitary adenomas). However, MRIs may fail to detect microadenomas smaller than 3 millimeters (1/8 inch). In addition, these scans often show small abnormalities of the pituitary that may be unrelated to the patient’s symptoms.
- Retinoblastoma. MRI may be used to evaluate the size and pattern of spread of this cancer of the eye.
- Lung cancer. MRI is useful in detecting cancer that has spread from the lungs to the brain, spinal cord or other organs.
- Prostate cancer. MRI provides a clear picture of the prostate, which can help a physician to diagnose the stage of the cancer. For example, MRI scans reveal whether or not the cancer has spread from the prostate into the seminal vesicles. This information will have a significant impact on treatment planning and the patient’s prognosis. In addition, MRI may help physicians evaluate a patient’s response to prostate cancer treatments.
- Endometrial cancer. MRI is now the chief means of comprehensively evaluating the female reproductive system. It is frequently used to diagnose the stage of endometrial cancer prior to surgery.
- Liver cancer. MRIs can help detect cancer that has spread (metastasized) from one area of the body to the liver.
- Breast cancer. Unlike CAT scans and x-rays, MRI does not reveal tiny mineral deposits (calcifications) that often suggest the presence of breast cancer. Special MRI machines are now available in some hospitals that are designed specifically for breast examinations. Research studies have now found that MRI may be more effective than ultrasound or mammography in detecting very early stages of breast cancer. Based on these studies, in 2007 The American Cancer Society (ACS) changed their official breast cancer screening guidelines.
For the first time, the ACS has included MRI in the guidelines for breast cancer screening. Women who are at high risk for breast cancer (defined as greater than 20 to 25 percent lifetime risk) should receive an MRI in addition to a mammogram every year. A woman’s risk is based on a number of factors including family history and the presence of certain breast cancer genes (e.g. BRCA1 or BRCA2 mutations). The ACS estimates that fewer than 1 in 50 women will need an annual breast MRI.
Researchers suggest that more studies are needed before MRI becomes the preferred breast cancer screening method. Although it may be more effective in detecting breast cancer, it is expensive and yields a high number of false-positive results, leading to further testing such as biopsies.
- Thyroid cancer. MRI can reveal the size of the tumor and whether it has spread to nearby tissues or the lymph nodes.
MRI can be used to diagnose and stage the following cancers:
|Bone & spinal cord||Bone & spinal cord|
|Soft tissue (muscle, tendons, fat)||Soft tissue (muscle, tendons, fat)|
|Non-Hodgkin’s lymphoma/ Hodgkin’s lymphoma||Non-Hodgkin’s lymphoma/ Hodgkin’s lymphoma|
|Bladder and ureter||Lung|
|Head and neck|
Before the MRI test
Typically, magnetic resonance imaging (MRI) is an outpatient procedure done at a hospital or clinic. Patients should closely follow their physician’s recommendations in preparing for the test. Usually, patients will be allowed to eat without restrictions and to take their usual medications. At the facility, patients may be asked to change into a gown or to wear clothing without fasteners, such as a sweatshirt and sweatpants. Bras with hooks or underwires may not be permitted, so women wearing them may be asked to change into a gown.
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):
- 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 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 the MRI. Patients with these devices should inform the physician and obtain clearance 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.
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. 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, an MRI is first taken without the use of the dye and a second scan is taken with the dye.
During and after the MRI
The MRI chamber is a relatively tight space, and individuals undergoing a scan may be required to lie still for an hour or more. Some people may feel uncomfortable or claustrophobic in this environment. In many machines, music through headphones or speakers can be played to help the patients relax. Individuals who become anxious in small spaces may want to discuss with their physician use of a sedative before 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. Open MRIs are not an option for the diagnosis of some conditions.
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. The patient may not be able to see the technician from the machine. 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 as it takes multiple views of the target site. These noises are a normal part of the MRI procedure. A nurse or technician provides instructions and 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. However, if a sedative is administered, patients will be monitored until the effects of the sedative have passed. Patients who have received sedatives 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 physician and a full report will be completed with the results. The report will be sent to the ordering physician as well as any other physicians designated by the patient. It is important for the patient to indicate which physicians, such as those on the cancer care team, should receive a copy of the report. The MRI results will help the patient’s physician determine the need for further tests and treatment.
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 before their appointment.
Potential risks with MRI
Pregnant women should avoid having an MRI unless absolutely necessary, because risk to the developing fetus is unknown.
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. This is due to a reaction between iron oxide or other metallic substances commonly found in tattoo ink 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.
Treatments that may follow MRI
Patients who are diagnosed with cancer may be treated with a variety of therapies based on a number of factors. In some cases, one form of treatment will be considered. In most cases, however, a combination of treatments will be used to fight the cancer. Commonly used treatments include:
- Chemotherapy. Uses one or more powerful drugs to destroy cancer cells to prevent them from growing, dividing and spreading throughout the body.
- Radiation therapy. Uses an energy called ionizing radiation to kill cancer cells and shrink tumors. Radiation targets fast-dividing cancer cells and disrupts or destroys their genetic material, preventing the cells from continuing to grow and spread throughout the body.
- Biological therapy. Repairs, stimulates or enhances the immune system so that it can better recognize and destroy cancer cells. Some forms of biological therapy directly attack cancer cells in treatment. This therapy is also used to blunt side effects associated with cancer treatments such as chemotherapy.
- Hormone therapy. Treatment for cancers that depend on hormones to grow and spread. Patients who undergo this treatment sometimes take medications that reduce the levels of certain hormones, such as estrogen (in women) and testosterone (in men). In other cases, patients may take drugs that prevent cancer from attaching to hormones that help the disease to thrive.
- Surgery. Used for the complete or partial removal of a tumor.
- Bone marrow transplants. Replace bone marrow damaged by cancer or cancer treatments with healthy marrow obtained from a donor. Bone marrow contains stem cells that produce red blood cells, white blood cells and platelets necessary for life.
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 uses 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 MRIs. 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 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 MRIs. New software has shown promise for early detection and treatment of breast cancer using serial-time images.
Questions for your doctor about 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 the following questions about magnetic resonance imaging (MRI):
- What do you hope to learn from my MRI?
- Why should I have an MRI instead of another imaging procedure such as a CAT scan?
- Should I have an annual MRI for breast cancer screening?
- Where should I have my MRI?
- How long will my MRI take to complete?
- Will my MRI be taken with or without dye?
- What are the chances I will have a reaction to the dye?
- What will be done if I have an allergic reaction?
- Can my scan be completed in an open MRI machine?
- Should I have a sedative before the test to avoid anxiety?
- When and from whom will I receive the results of the MRI?
- How often will I need MRIs for my condition?
- What test will be substituted if I cannot have an MRI?
- How can I obtain copies of my MRI films?