Magnetic Resonance Imaging (MRI) – Body
Magnetic resonance imaging (MRI) of the body uses a powerful magnetic field, radio waves and a computer to produce detailed pictures of the inside of your body. It may be used to help diagnose or monitor treatment for a variety of conditions within the chest, abdomen, and pelvis. If you’re pregnant, body MRI may be used to safely monitor your baby.
Tell your doctor about any health problems, recent surgeries or allergies and whether there’s a possibility you are pregnant. The magnetic field is not harmful, but it may cause some medical devices to malfunction. Most orthopedic implants pose no risk, but you should always tell the technologist if you have any devices or metal in your body. Guidelines about eating and drinking before your exam vary between facilities. Unless you are told otherwise, take your regular medications as usual. Leave jewelry at home and wear loose, comfortable clothing. If you have claustrophobia or anxiety, you may want to ask your doctor for a mild sedative prior to the exam.
What is MRI of the Body?
Magnetic resonance imaging (MRI) is a noninvasive medical test that physicians use to diagnose medical conditions.
MRI uses a powerful magnetic field, radio frequency pulses and a computer to produce detailed pictures of organs, soft tissues, bone, and virtually all other internal body structures. MRI does not use ionizing radiation (x-rays).
Detailed MR images allow physicians to evaluate various parts of the body and determine the presence of certain diseases. The images can then be examined on a computer monitor, transmitted electronically, printed or copied to a CD or uploaded to a digital cloud server.
What are some common uses of the procedure?
MR imaging of the body is to evaluate:
- organs of the chest and abdomen—including the heart, liver, biliary tract, kidneys, spleen, bowel, pancreas, and adrenal glands.
- pelvic organs including the bladder and the reproductive organs such as the uterus and ovaries in females and the prostate gland in males.
- blood vessels (including MR Angiography).
- lymph nodes.
Physicians use an MR examination to help diagnose or monitor treatment for conditions such as:
- tumors of the chest, abdomen or pelvis.
- diseases of the liver, such as cirrhosis, and abnormalities of the bile ducts and pancreas.
- inflammatory bowel disease such as Crohn’s disease and ulcerative colitis.
- heart problems, such as congenital heart disease.
- malformations of the blood vessels and inflammation of the vessels (vasculitis).
- a fetus in the womb of a pregnant woman.
What does the equipment look like?
The traditional MRI unit is a large cylinder shape tube that surrounds a circular magnet. You will lie on a moveable examination table that slides into the center of the magnet.
Some MRI units, called short-bore systems, are designed so that the magnet does not completely surround you. Some newer MRI machines have a larger diameter bore which can be more comfortable for larger size patients or patients with claustrophobia. Other MRI machines are open on the sides (open MRI). Open units are especially helpful for examining larger patients or those with claustrophobia. Newer open MRI units provide very high-quality images for many types of exams. Older open MRI units may not provide this same image quality. We cannot perform certain types of exams using open MRI. For more information, consult your radiologist.
The computer workstation that processes the imaging information is located in a separate room from the scanner.
How does the procedure work?
Unlike conventional x-ray examinations and computed tomography (CT) scans, MRI does not utilize ionizing radiation. Instead, radiofrequency pulses re-align hydrogen atoms that naturally exist within the body. This does not cause any chemical changes in the tissues. As the hydrogen atoms return to their usual alignment, they emit different amounts of energy depending on the type of body tissue they are in. The MR scanner captures this energy and creates a picture of the tissues scanned based on this information.
The magnetic field produces by passing an electric current through wire coils in most MRI units. Other coils, located in the machine and in some cases, placed around the part of the body being imaged, send and receive radio waves, producing signals that are detected by the coils. The electric current does not come in contact with the patient.
A computer then processes the signals and generates a series of images, each of which shows a thin slice of the body. The images can then be studied from different angles by the interpreting radiologist.
Frequently, the differentiation of abnormal (diseased) tissue from normal tissues is better with MRI than with other imaging modalities such as x-ray, CT, and ultrasound.
Who interprets the results and how do I get them?
A radiologist, a physician specifically trained to supervise and interpret radiology examinations. It will analyze the images and send a signed report to your primary care or referring physician.
Follow-up examinations may be necessary. Your doctor will explain the exact reason for another exam. Sometimes a follow-up exam is because a potential abnormality needs further evaluation with additional views or a special imaging technique. A follow-up examination may also be necessary so that any change in a known abnormality can be monitored over time. Follow-up examinations are sometimes the best way to see if treatment is working or if a finding is stable or changed over time.
What are the benefits vs. risks?
- MRI is a noninvasive imaging technique that does not involve exposure to ionizing radiation.
- MR images of the soft-tissue structures of the body—such as the heart, liver and many other organs— is more likely in some instances to identify and accurately characterize diseases than other imaging methods. This detail makes MRI an invaluable tool in early diagnosis and evaluation of many focal lesions and tumors.
- MRI has proven valuable in diagnosing a broad range of conditions, including cancer, heart and vascular disease, and muscular and bone abnormalities.
- MRI allows physicians to assess the biliary system noninvasively and without contrast injection.
- The contrast material used in MRI exams is less likely to produce an allergic reaction than the iodine-based contrast materials used for conventional x-rays and CT scanning.
- MRI provides a noninvasive alternative to x-ray, angiography, and CT for diagnosing problems of the heart and blood vessels.
- The MRI examination poses almost no risk to the average patient with appropriate safety guidelines.
- There are risks of excessive sedation. However, the technologist or nurse will monitor your vital signs to minimize this risk.
- Although the strong magnetic field is not harmful in itself, implanted medical devices that contain metal may malfunction or cause problems during an MRI exam.
- Nephrogenic systemic fibrosis is currently a recognized, but rare, a complication of MRI believed to be caused by the injection of high doses of gadolinium-based contrast material in patients with very poor kidney function. Careful assessment of kidney function before considering a contrast injection minimizes the risk of this very rare complication.
- There is a very slight risk of an allergic reaction if we inject contrast material. Such reactions are usually mild and easily controlled by medication. If you experience allergic symptoms, a radiologist or other physician will be available for immediate assistance.
- Manufacturers of intravenous contrast indicate mothers should not breastfeed their babies for 24-48 hours after contrast medium is given. However, both the American College of Radiology (ACR) and the European Society of Urogenital Radiology note that the available data suggest that it is safe to continue breastfeeding after receiving intravenous contrast. For further information please consult the ACR Manual on Contrast Media and its references.
What are the limitations of MRI of the Body?
Assure high-quality images only if you are able to remain perfectly still and follow breath-holding instructions while recording the images. If you are anxious, confused or in severe pain, you may find it difficult to lie still during imaging.
A person who is very large may not fit into the opening of certain types of MRI machines.
The presence of an implant or other metallic objects sometimes makes it difficult to obtain clear images due to streak artifacts from the metallic objects. Patient movement can have the same effect.
A very irregular heartbeat may affect the quality of images obtained using techniques that time the imaging based on the electrical activity of the heart, such as electrocardiography (EKG).
Breathing may cause artifacts, or image distortions, during MRIs of the chest, abdomen, and pelvis. Bowel motion is another source of motion artifacts in the abdomen and pelvic MRI studies. This is less of a problem with state-of-the-art scanners and techniques.
Although there is no reason to believe that magnetic resonance imaging harms the fetus, advice pregnant women not to have an MRI exam during the first trimester unless medically necessary.
MRI may not always distinguish between cancer tissue and fluid, known as edema.
MRI typically costs more and may take more time to perform than other imaging modalities.