Q: I have been asked to undergo a MRI scan. I know it is a safe technique, but please tell me what it is all about.
A: A safe, non-invasive procedure that uses powerful magnets and radio waves to construct pictures of the body, Magnetic Resonance Imaging [MRI], unlike an X-ray with its radiation effects, can provide additional imaging information for the clinician, or doctor. It, therefore, helps in making a safe, more accurate diagnosis.
A MRI makes use of radio waves very close in frequency to those of FM radio stations. Hence, the scanner, as you will see when you undergo the test, will be placed within a specially shielded room to avoid outside interference. You will be asked to lie down on a narrow table which slides into a large tunnel-like tube within the scanner.
The MRI has small devices, or body coils, which are placed around your head, arm, or leg, or next to other areas which your doctor wants to study. The body coils are specially made to remit and receive radio wave pulses and also improve the image quality. You will be given intravenous [IV] fluid in a small vein of the hand, or forearm.
A MRI is operated by a technologist trained in operating the machine. The doctor can observe the entire study from an adjoining room.
During a MRI procedure, one may need to take several sets of images. Each image may last from 2 to 15 minutes. A complete scan, depending on the organs studied, sequences performed, and need for contrast enhancement, may take up to an hour or so. Today, there are newer, more advanced scanners, with more powerful magnets which can complete the process in quick time.
For a MRI scan to be done, there is no need for preparatory tests, diet, or medications. The scan can be performed immediately after other imaging studies. However, subject to the nature of the study, it is not uncommon for patients to be asked to fast for at least 4-5 hours before the procedure.
Since very powerful and strong magnets are used in the machine, certain metallic objects are barred. You should, therefore, not carry any of the following items —
- Jewellery, watches, credit cards, and hearing aids
- Pins, hairpins, metal zippers, and other metallic items
- Pens, pocket-knives, and eyeglasses
- Implanted metallic objects
- Removable dental work should also be taken out just prior to the scan
- People who have cardiac pacemakers, artificial heart valves, or joints, ear implants etc., cannot undergo the procedure.