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. 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 internal injuries, joint and bone disorders and various diseases, such as arthritis and cancer. The only preparation for an MRI involves removing all metal objects, such as jewelry, from the body.
MRI is used to detect abnormalities or problems in nearly every part of the body, including:
Musculoskeletal system
Blood vessels
Head and brain
Heart and chest
Abdomen and pelvis
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 should consult a physician to find out if an MRI is allowed. In all cases, patients should inform the physician or technician of any metal objects present in their bodies. Pregnant women should generally avoid MRIs because the risk to the fetus is unknown. However, there may be some instances when an MRI is warranted in pregnant patients.
Patients who are nervous in small spaces may wish to ask their physician about the possibility of receiving a sedative during the procedure, which may take up to one hour or longer in a tight space. Using a less enclosed type of MRI machine may be another option. If patients receive a sedative, then they will need someone to drive them home from the test. Otherwise, patients are free to go about their daily activities after the test is completed.
About MRI
Magnetic resonance imaging (MRI) uses a powerful magnetic field to create images of structures and organs within the body. It is a safe and noninvasive or minimally invasive test that can help physicians diagnose a wide range of diseases and conditions without subjecting the patient to radiation or radioactive isotopes.
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.
Because the MRI provides such clear images of the soft-tissue structures near and around the bones, it is the most sensitive test for examination of the body’s major joints, including the spine and the soft tissues of the limbs. MRI images can allow physicians to locate and identify the cause of pain, inflammation or bleeding in the tissues in and around the joints and bones. The images are so detailed that they allow physicians to see even the smallest tears and injuries to the ligaments and muscles as well as some fractures that x-rays cannot see.
MRI is widely used to diagnose sports injuries (e.g., fractures, tendinitis, ligament tear, knee meniscus injury), workplace disorders caused by repeated strain or use of force, and conditions such as carpal tunnel syndrome. MRI images can provide physicians with a clear picture of degenerative diseases such as arthritis, deterioration of joint surfaces, narrowing of the spinal canal (spinal stenosis) or a herniated disc. An MRI image of the brain can be part of a diagnosis of fibromyalgia.
Neurosurgeons often use MRI to evaluate a patient’s spinal cord following an acute injury or trauma. MRI is also useful for the detection and diagnosis of infections, such as septic arthritis or osteomyelitis (bone infection), and tumors involving the musculoskeletal system.
Other conditions revealed by MRI include:
Eye or inner-ear tissue abnormalities
Cardiac damage caused by heart attack, heart disease or conditions such as sarcoidosis
Blood vessel plaques and blockages
Functional disorders of organs, such as the lungs, liver, pancreas, kidneys and spleen
Strokes and chronic disorders of the nervous system
Brain abnormalities in patients with dementia
Diseases of the pituitary gland
Reproductive system and bladder problems
Detection and staging of various forms of cancer
Sometimes MRI involves injection of a contrast medium (dye) into a vein that increases the clarity of the images by making the body’s tissues more responsive to the machine’s magnetic and radio waves. MRI is painless other than the brief discomfort of an injection and possible mild cramping from holding the body in position.
Types and differences of MRI
Almost every part of the body may be studied with magnetic resonance imaging (MRI). The clear pictures obtained from an MRI often provide physicians with information not available through other diagnostic tests such as x-rays, and in some cases may even eliminate the need for exploratory surgery such as arthroscopy.
To gather information about various conditions affecting the body, including those causing unexplained chronic pain, physicians may use several types of MRI scanners, including:
Standard MRI. This scanner resembles a long cylinder with a narrow tube in the center. A patient lies on a moveable bed and the whole body is inserted inside the tube. Although this machine may be confining for some people, it produces the clearest images.
Short-bore MRI. This scanner is similar to the standard, except only half the size. Depending on which areas of the body are being tested, patients position their bodies so that the part being scanned lies within the tube. People who experience anxiety in enclosed spaces may prefer this scanner.
Open MRI. This scanner, which is often shaped somewhat like the letter “C,” may be an option for obese or claustrophobic patients because there is additional room inside the machine. Some facilities offer upright open MRIs in which the patient stands. However, the images produced by open MRIs are not as detailed as those of other MRI scanners.
Researchers are constantly trying to improve MRI and other diagnostic technologies. Newer types of MRI, whose availability may be limited, include:
3.0-Tesla MRI. The strength of MRI is rated in units called Tesla units, with standard high-field MRI at 1.0 to 1.5 Teslas. Some facilities now have powerful 3.0-Tesla and 4.0-Tesla MRI, and 7.0-Tesla MRI is being developed for brain imaging. Research has indicated that 3.0-Tesla MRI can diagnose shoulder cartilage tears noninvasively with an accuracy comparable to that of arthroscopy.
High-resolution prostate MRI. Scientists at Johns Hopkins University and elsewhere are working to make advanced MRI available soon to provide the first reliable screening for prostate cancer, to avoid blind biopsies and questionable blood tests, physical examinations and ultrasounds.
Voxel-based morphometry (VBM). This permits very sensitive measures of small sections of the brain. VBM has been used in studying conditions such as depression.
Magnetic resonance spectroscopic imaging (MRSI). Spectroscopy uses means such as prisms to split radiant energy into its wavelengths or frequencies. Spectroscopic MRI has been found useful in diagnosing cancer.
Nuclear magnetic resonance (NMR) spectroscopy. This low-energy technique avoids deposits of heat in patients and medical staff by detecting “nuclear spin” of particles. A goal is to create a portable, lightweight variation of MRI.
Whole-heart MRI. A potential noninvasive alternative to procedures such as cardiac catheterization in detecting coronary artery disease.
Real-time functional magnetic resonance imaging (rtfMRI). In addition to its diagnostic uses, MRI may have a role in pain management by providing a kind of biofeedback. Researchers have used rtfMRI to provide chronic pain patients with live, visual images of pain centers in their brain. With real-time MRI, some patients have been able to ease their pain by applying mental strategies similar to guided imagery.
Before the MRI
Typically, magnetic resonance imaging (MRI) is an outpatient test performed 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. 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.
It is important for the patient to remove all personal metal objects (e.g., jewelry, watches, hairpins, digital devices) prior to the test. Patients may want to leave these objects at home. Additionally, 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 a spinal pump or implantable insulin pump
MRI may be allowed with some types of medical devices, such as artificial joints and certain types of stents and heart valves. Sometimes a specified period of time must have elapsed. Such patients should inform the physician and get clearance before an MRI. If patients suspect that they have a metal device or fragment (such as from an injury) inside their body, an MRI might not be an option.
Sometimes MRI involves injection of a contrast medium (dye) into a vein in the arm or hand shortly before the procedure. 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.
During and after the MRI
The magnetic resonance imaging (MRI) chamber is a relatively tight space, and individuals undergoing a scan are required to lie still for up to one hour, sometimes as long as two hours.
Some people may feel uncomfortable or claustrophobic in this environment. Sometimes radios are available to help patients relax, but those who become very anxious in small spaces may want to discuss with their physician the possibility of receiving a mild sedative during 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, so the images are not as clear.
The patient is placed on a long bed that slides into the MRI chamber. The individual 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. The MRI equipment will make many 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 will periodically make sure that the patient is comfortable and able to continue.
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. They will then need a friend or relative to drive them home.
Results of the test are recorded on film. After receiving the radiology report, the physician will be more prepared to confirm a diagnosis or prescribe further tests and treatments.
Potential risks with MRI
Pregnant women should avoid having a magnetic resonance imaging (MRI) test 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 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 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. An individual may experience nausea, headache or pain at the site of injection.
Questions for your doctor regarding MRI
Preparing questions in advance can help patients to 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):
Why is an MRI being ordered for me? Why is it recommended for me over another type of test, such as an x-ray?
Do I have any implants or conditions that rule out use of an MRI?
Which type of MRI will I have?
What information about me will the MRI provide you?
Will my MRI cause me pain or discomfort?
Will I be injected with a contrast medium? What does this dye do?
Where and when is my test taking place?
How should I prepare for my MRI?
How is an MRI performed? What should I expect during the test?
What options are there if I’m claustrophobic or very sensitive to noise?
When will my results be ready, and who will explain them to me?
Is real-time MRI a treatment option to help me control my pain?
