What is MRI of the Body? Magnetic resonance imaging (MRI) uses radiofrequency waves and a strong
magnetic field rather than |
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What are some common uses of the MRI procedure?Because
MRI
can give such clear pictures of soft-tissue structures near and around
bones, it is the most sensitive exam for spinal and joint problems. MRI
is widely used to diagnose In addition, MRI of the heart, aorta, coronary arteries, and blood vessels is a fast, noninvasive tool for diagnosing coronary artery disease and heart problems. Physicians can examine the size and thickness of the chambers of the heart, and determine the extent of damage caused by a heart attack or progressive heart disease. Organs of the chest and abdomenincluding the lungs,
liver,
kidney,
spleen,
pancreas,
and abdominal vesselscan also be examined in high detail with MRI,
enabling the diagnosis and evaluation of tumors and functional disorders.
MRI is growing in popularity as an alternative to traditional |
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How should I prepare for the procedure?Because the strong magnetic field used for MRI will pull on any ferromagnetic metal object implanted in the body, MRI staff will ask whether you have a prosthetic hip, heart pacemaker (or artificial heart valve), implanted port, infusion catheter (brand names Port-o-cath, Infusaport, Lifeport), intrauterine device (IUD), or any metal plates, pins, screws, or surgical staples in your body. In most cases, surgical staples, plates, pins and screws pose no risk during MRI if they have been in place for more than four to six weeks. Tattoos and permanent eyeliner may also create a problem. You will be asked if you have ever had a bullet or shrapnel in your body, or ever worked with metal. If there is any question of metal fragments, you may be asked to have an x-ray that will detect any such metal objects. Tooth fillings usually are not affected by the magnetic field, but they may distort images of the facial area or brain, so the radiologist should be aware of them. The same is true of braces, which may make it hard to "tune" the MRI unit to your body. You will be asked to remove anything that might degrade MRI images of the head, including hairpins, jewelry, eyeglasses, hearing aids, and any removable dental work. The radiologist or technologist may ask about drug allergies and whether head surgery has been done in the past. If you might be pregnant, this should be mentioned. Some patients who undergo MRI in an enclosed unit may feel confined or claustrophobic. If you are not easily reassured, a sedative may be administered. Roughly one in 20 patients will require medication to reduce the anxiety associated with claustrophobia. |
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What does the MRI equipment look like?The conventional MRI
unit is a closed cylindrical magnet in which the patient must lie totally
still for several seconds at a time, and consequently may feel The Examples of the radiography equipment that may be used are shown at the top of this page. |
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How does the procedure work?MRI
is a unique imaging method because, unlike the usual radiographs |
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How is the procedure performed?The patient is placed on a sliding table and positioned comfortably for the MRI examination. Then the radiologist and technologist leave the room and the individual MRI sequences are performed. The patient is able to communicate with the radiologist or technologist at any time using an intercom. Also, many MRI centers allow a friend or, if a child is being examined, a parent to stay in the room. Depending on how many images are needed, the exam will generally take 15 to 45 minutes, although a very detailed study may take longer. You will be asked not to move during the actual imaging process, but between sequences some movement is allowed. Patients are generally required to remain still for only a few seconds to a few minutes at a time. Depending on the part of the body being examined, a contrast
material may be used to enhance the visibility of certain tissues
or blood vessels. A small needle connected to an intravenous line is
placed in an arm or hand vein. A saline solution will drip through the
intravenous line to prevent clotting until the contrast material is
injected, about When the exam is over the patient is asked to wait until the images are examined to determine if more images are needed. A radiologist experienced in MRI will analyze the images and send a report with his or her interpretation to the patient's personal physician. This should take only a few days or less. |
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What will I experience during the MRI procedure?MRI causes no pain, but some patients can find it uncomfortable to remain still during the examination. Others experience a sense of being "closed in," though the more open construction of newer MRI systems has done much to reduce that reaction. You may notice a warm feeling in the area under examination; this is normal, but if it bothers you the radiologist or technologist should be notified. If a contrast injection is needed, there may be discomfort at the injection site, and you may have a cool sensation at the site during the injection. Most bothersome to many patients are the loud tapping or knocking noises heard at certain phases of imaging. Ear plugs may help. |
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Who interprets the results and how do I get them?A radiologist, who is a physician experienced in MRI and other radiology examinations, will analyze the images and send a signed report with his or her interpretation to the patient's personal physician. The patient receives MRI results from the referring physician who ordered the test. New technology also allows for distribution of diagnostic reports and referral images over the Internet at many facilities. |
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What are the benefits vs. risks?Benefits
Risks
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What are the limitations of MRI of the Body?Bone is better imaged by conventional To locate a medical imaging or radiation oncology provider in your community, you can search the ACR-accredited facilities database. This procedure is reviewed by a physician with expertise in the area presented and is further reviewed by committees from the American College of Radiology (ACR) and the Radiological Society of North America (RSNA), comprising physicians with expertise in several radiologic areas. |
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This page was reviewed on: June 1, 2004 |