Magnetic Resonance Imaging (MRI)
Description: An MRI machine or scanner uses a powerful magnet and radio waves linked to a computer to create remarkably clear and detailed cross sectional images of the body. To visualize an MRI, think of your body as a loaf of bread with its many slices. The MRI allows the physician to see many different “slices” of a body part by taking pictures from outside the body. The “slices” can be displayed on a video monitor and saved on film or disk for analysis.
For some MRI studies, a contrast agent, usually gadolinium may be used to enhance the visibility of certain tissues. The contrast agent is given via a small intravenous (IV) line placed in a vein in your arm. See ACRIN’s “About Imaging Agents or Tracers” Information page for more information.
Examples of Uses: MRI can be used to view, monitor, or diagnose:
- spine, joint or muscle problems
- abdominal tumors and disorders
- brain tumors and abnormalities
- breast cancer
- heart or blood vessel problems
Specialized MRI techniques: Sometimes an MRI scan will include a special method that provides additional information to your physician. Some specialized MRI techniques are described below.
Diffusion MRI- Shows the microscopic movement of water molecules within tissue. It can provide information on the microstructure of the tissue as well as swelling within tissues. This method has been used primarily with brain pathology, but is being studied for other uses.
Dynamic Contrast Enhanced MRI (DCE-MRI) – Uses a continuous series of images taken before, during and after injection of a contrast agent (much like a movie or video). DCE-MRI can provide information about tumor blood flow.
Magnetic Resonance Angiography (MRA)- Uses a magnetic field and radio wave energy to look at blood vessels, most often the arteries in or near the heart, brain, abdomen or legs. . A contrast or imaging agent is often used to make the blood vessels show up more clearly on the image,
Magnetic Resonance Spectroscopy (MRS)- Provides important information about the chemical activity within cells . Some tumors are known to contain high levels of specific chemicals. MRS can also be used to identify the size and stage of a tumor. Often the MRS results are combined with MRI results to help doctors understand the area of interest more completely.
Perfusion MRI- Shows blood flow within the smallest blood vessels (capillaries) within tissue. This scan provides information related to both amount of blood flow and the time involved. A contrast agent is often used. This method has been used primarily with brain related problems, such as stroke and tumors, but can be used in any situation where blood flow is a critical issue.
Preparation: Before an MRI, eat normally and take your usual medications unless otherwise instructed. You will be given a hospital gown to wear or instructed to wear loose clothing without metal fasteners. Remove all accessories, such as jewelry or hair pins/clips. Also remove wigs, dentures, glasses, and hearing aids. Metal objects may interfere with the magnetic field during the exam, affecting the quality of the MRI images. The magnetic field may damage electronic items. Tell the technologist (the person performing the MRI) if you have any of the following:
· prosthetic joints
· pacemaker, defibrillator, or artificial heart valve
· implanted venous access device
· cochlear/inner ear implants
· spinal stimulator
· intrauterine device (IUD)
· metal plates, pins, screws, staples or bullets/shrapnel
· tattoos or permanent make-up
· transdermal patch
· anxiety in confined spaces (claustrophobia)
If you are pregnant or suspect you may be pregnant, tell the technologist.
During the Exam: A conventional MRI unit is a large cylindrical magnet with a central opening. A sliding table rests in the opening. You will lie on the narrow table and be comfortably positioned. A small coil may be placed around the area being examined. The table will then be slid into the opening. The technologist will be in an adjoining room, but can see, hear, and speak to you at all times. In some cases a friend or family member may stay in the room with you. During the exam you will need to remain very still. An MRI exam usually consists of several sequences, each lasting 2-15 minutes. Slight movement between sequences is allowed. The exam is painless. You may feel warmth in the area being examined.
“Short bore” systems are shorter and wider and do not totally enclose the patient. “Open” MRI systems are available for those who are unable to use a conventional MRI; however the image quality varies.
Time Required: 30 to 45 minutes
Noise During Exam: Loudtapping or thumping. Earplugs or earphones may be provided to help block the noise. The technologist will talk to you throughout the exam.
Space During Exam: The MRI opening is usually between 21-26 inches wide. The opening in the MRI scanner is 5-8 feet long. During the exam, you may feel “closed in” or claustrophobic. If this is a concern, speak to your doctor when the MRI is scheduled. Your doctor may suggest a mild sedative to help you feel more comfortable during the MRI exam. The MRI technologist is experienced in working with people who are uncomfortable in close spaces.
· MRI can help evaluate the function as well as the structure of many organs.
· Soft tissue structures (heart, lungs, liver, and other organs) are clearer and more detailed with MRI than other imaging methods.
· MRI provides a fast, non-invasive alternative to x-ray angiography.
· MRI uses no ionizing radiation.
· There are no known harmful effects from exposure to the magnetic field or radio waves used in MRI imaging.
· MRI is generally avoided in the first 12 weeks of pregnancy. In such cases, other imaging methods are used unless there is a strong medical reason to use MRI.
· An undetected metal implant may be affected by the strong magnetic field.
· There is a rare risk of a major allergic reaction to the contrast agent.
· There is a rare risk of complications from the use of gadolinium in those who have kidney disease. Those with kidney disease may be asked to have a blood test before their MRI in order to check their kidney function.
A radiologist, who is a physician with specialized training in MRI and other imaging tests, will analyze and interpret the results of your MRI scan and then send a report to your personal physician. It usually takes a day or so to interpret, report, and deliver the results. Contact your personal physician for information on the results of your exam.