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MRI - Magnetic Resonance Imaging
Overview
Magnetic resonance, or MR, is an imaging system that allows doctors to look
inside of the human body without using x-rays. MR uses a large magnet, radio
waves, an antenna and sophisticated computer processing to produce the images.
MR images
complement other imaging tests because of
their ability to differentiate between tissue types and
to identify very subtle areas of abnormality. In
many disease types, MR images are able to
more accurately identify the type of abnormality
and its extent than other types of imaging, and
as a result, can reduce the need for surgical
evaluation.
MR is used to diagnose cancers, musculoskeletal problems, brain and other
nervous system disorders including stroke, traumatic injuries, multiple
sclerosis and tumors.
How does MR imaging work?
The human body is made up of millions of atoms that are magnetic. Normally,
protons inside the atoms spin randomly. The magnet in the MR causes some of
the protons to spin in the same direction. Radio waves then make the protons
move out of alignment. When the radio waves are stopped, the protons once
again line up and then release energy. A receiver coil measures both the
energy released and the time it takes for the protons to line up again.
The measurements are transferred to a computer that constructs a black
and white image from the information. Any metallic object can interfere with the MR machine’s magnet, stop its functioning or create a hazard. These include:
- Cardiac pacemakers
- Cerebral aneurysm clips
- Insulin pumps or other infusion pumps
- Cochlear (inner ear) implants
- Neurostimulators
- Other metal in the body, especially in your eyes
Common MRI Exam Questions
How is the procedure performed?
You will be asked to lie down on the table connected to the MRI machine.
Other small MRI coils may be placed over or under you. These act as a receiver
for the radio waves. A contrast dye may be used to highlight certain tissues.
If dye is used, you will receive it via an injection into your vein. All
contrast agents are approved by the Food and Drug Administration and are
considered to be safe. You will be offered a headset and headphones so that
you can listen to music if you wish. The table will slide inside the machine
to start the exam. Even with the headset, you will hear a loud thumping
noise. This is normal. You will not feel the magnetic fields or radio waves.
You will need to be completely still for the exam. Occasionally the technologist
will ask you to hold your breath; keeping still prevents the images from
blurring.
What if I'm claustrophobic?
Please let both your doctor and the technologist know if you are claustrophobic.
If you wish, you may be given a sedative to make the procedure more relaxing.
During the procedure, the technologist will watch you through an observation
window, a two-way intercom may be used for communication and you may talk
to the technologist if you become anxious. You may also have a friend
or family member stay in the room with you during the exam. Parents may
stay with their child.
Is the exam safe?
MRI uses no x-rays. The magnetic fields used during the exam are not harmful.
Please let the technologist know if you have had reactions to contrast
agents in the past. Oral and/or intravenous dyes may be used, depending
on the type of exam. These contrast agents are generally safe but, as with
all medications, side effects can occur. A small percent of patients are
allergic to the intravenous agent. Allergic reactions are usually mild
(itching, flushing) but occasionally may be severe. If you have had allergic
reactions to dyes or contrast agents before, or if you have multiple allergies,
you may be at higher risk for a reaction. Let your doctor know if you
have any of these conditions when scheduling your exam. As with any medical
procedure, please let the technologist know if you are or may be pregnant.
What preparation is needed?
Usually no special preparation is required for an MRI exam.
What should I wear?
Wear comfortable cotton clothing without metal snaps. You
may be asked to change into a patient gown or scrubs.
How long will the MRI take?
Please arrive 15 minutes prior to your exam time to verify registration
information and prepare for the exam. The length of time for the exam
depends upon the part of the body being imaged. Generally speaking, you
should plan on one hour for the MRI exam. If multiple areas of your body
are being imaged, the exam may take longer.
What can I expect after the exam?
If you've had a sedative, you will need to have someone to drive you home,
and you may be asked to stay a short time after your exam until you are
awake and alert.
When will my physician get the results?
One of our radiologists will study the images and send a written report to your physician within one to two business days.
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