MRI
MRI (magnetic resonance imaging) is a diagnostic procedure that combines a powerful magnet, radio waves and computer technology to provide detailed images of tissues, muscles, nerves and bones. Because MRI uses magnetic force and radio waves to create images, there is no radiation exposure during the procedure. MRI is often used instead of CT to study soft tissues or organs because bones do not obscure the organs and soft tissues as they do with CT imaging.
MRI can be used to assess everything from ruptured discs in the spine to detecting brain tumors and vascular diseases through techniques such as:
- Breast MRI can be a more effective imaging technique than mammography for some women, and can provide additional details for diagnosing and evaluating breast abnormalities.
- Spectroscopy (MRS) assesses chemical abnormalities in the brain for conditions such as coma, Alzheimer's disease, stroke, brain tumors, head injury and MS.
- Angiography (MRA) evaluates blood flow, or detects brain aneurysms or blood vessel abnormalities. It is used to visualize renal, carotid and vertebral arteries, or examine the aorta for aneurysm.
- Perfusion and diffusion scanning examines blood flow through tissues to evaluate strokes.
The Technology
You will be imaged in a tubular device approximately 24 inches (60 cm) in diameter. If your feet or knees are being imaged, your head will be outside of the magnet. If your head, shoulder, or chest is being imaged, your feet will be outside of the imager. Some claustrophobic individuals get anxious in situations like this, but be assured that you are in constant intercom contact with the technologists in the control room and can get out at any time. When you first lie on the bed of the imager, the technologist will move your body to position a specific area of your body at a crossed light beam. This spot on your body will be advanced to the isocenter of the magnet before the scan begins. This process is called landmarking.
The Exam
Your exam will last between 30 and 60 minutes. You will need to lie still for periods of 3 to 10 minutes at a time while the series of images are collected. You can breathe freely during this time. You may, in some cases, be allowed to move slightly between scans, but not so much that your position changes dramatically. The imaging session creates a series of repetitive knocking sounds when the magnetic field gradients are turned on and off during the procedure.
The Results
In medicine, the diagnosis of disease is rarely the result of a single exam or test performed by a single individual. Your primary care physician takes advantage of input from many specialists. One of these specialists is the radiologist. A radiologist is a medical doctor trained to interpret the information in magnetic resonance images. A radiologist will read the magnetic resonance images from your scan, and provide your physician with a report. Your physician will share the findings from the radiologist and other medical specialists with you.