MRI is a noninvasive imaging procedure that creates detailed, high resolution images of our body’s organs, tissues and skeletal system. MRI uses a magnet field and radio waves to construct these images. No radiation is involved. The MRI machine is a large, tube-shaped magnet. When you lie inside the machine, the magnetic field temporarily aligns all the water molecules in your body. Radio waves cause these aligned particles to product very faint signals, which are used to create cross-sectional images of your body – like slices in a loaf of bread. The MRI machine can combine these slices to produce 3-D images that may be viewed from many different angles.
How the test is performed
You may be asked to wear a hospital gown or clothing without metal fasteners. You will be asked to lie on a narrow table which slides into the middle of the MRI machine. If you have a fear of confined spaces, tell your doctor before the exam. You may be prescribed a mild sedative or your doctor may recommend an “open” MRI, in which the machine is not as close the body. Small devices called coils may be placed around the head, arm or leg or other areas to be studied. These devices help send and receive the radio waves and improve the quality of the images. Certain exams require that a special dye be given before the test. The dye is usually given through an intravenous line (IV) in your hand or forearm. The contrast helps the radiologist see certain areas more clearly. During the MRI, the person who operates the machine will watch you from a room next door. Several sets of images are usually needed each taking from 2 to 15 minutes each. Depending on the areas being studied and type of equipment, the exam may take 1 hour or longer.
How to prepare for the test
An MRI can be performed immediately after other imaging studies. Depending on the area of interest, the patient may be asked to fast for 4-6 hours prior to the scan. Other preparations are usually not needed. The strong magnetic fields created during an MRI can interfere with certain implants, particularly pacemakers. Persons with cardiac pacemakers can not receive an MRI and should not enter an MRI area.
What are the risks
There is no ionizing radiation involved in MRI and there have been no documented significant side effects of the magnetic fields and radio waves used on the human body to date. The most common type of contrast used is gadolinium. It is very safe. Allergic reactions to the substance rarely occur. The person operating the machine will monitor your heart rate and breathing as needed.
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