What is MRI?
Magnetic resonance imaging (MRI) is a noninvasive medical test that helps physicians diagnose and treat medical conditions. MR imaging 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.
What are some common uses of the procedure?
- organs of the chest and abdomen—including the heart, liver, biliary tract, kidneys, spleen, bowel, pancreas and adrenal glands.
- pelvic organs including the reproductive organs in the male (prostate and testicles) and the female (uterus, cervix and ovaries).
- blood vessels (MR Angiography).
Physicians use the MR examination to help diagnose or monitor treatment for conditions such as:
- tumors of the chest, abdomen or pelvis.
- certain types of heart problems.
- blockages or enlargements of blood vessels, including the aorta, renal arteries, and arteries in the legs.
- diseases of the liver, such as cirrhosis, and that of other abdominal organs, including the bile ducts, gallbladder, and pancreatic ducts.
- diseases of the small intestine, colon, and rectum.
- cysts and solid tumors in the kidneys and other parts of the urinary tract.
- tumors and other abnormalities of the reproductive organs (e.g., uterus, ovaries, testicles, prostate).
- causes of pelvic pain in women, such as fibroids, endometriosis and adenomyosis.
- suspected uterine congenital abnormalities in women undergoing evaluation for infertility.
- breast cancer and implants.
How does the procedure work?
Unlike conventional x-ray examinations and computed tomography (CT) scans, MRI does not depend on ionizing radiation. Instead, while in the magnet, radio waves redirect the axes of spinning protons, which are the nuclei of hydrogen atoms, in a strong magnetic field.
The magnetic field is produced 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.
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 physician.
Overall, the differentiation of abnormal (diseased) tissue from normal tissues is often better with MRI than with other imaging modalities such as x-ray, CT and ultrasound.
What are the benefits ?
- 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 enables the discovery of abnormalities that might be obscured by bone with other imaging methods.
- 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.
What are the limitations of MRI?
High-quality images are assured only if you are able to remain perfectly still or hold your breath, if requested to do so, while the images are being recorded. 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 a conventional MRI machine.
The presence of an implant or other metallic object sometimes makes it difficult to obtain clear images and patient movement can have the same effect.
Breathing may cause artifacts, or image distortions, during MRIs of the chest, abdomen and pelvis. Bowel motion is another source of motion artifacts in 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, pregnant women usually are advised not to have an MRI exam unless medically necessary.
MRI may not always distinguish between cancer tissue and edema fluid.
MRI typically costs more and may take more time to perform than other imaging modalities.