The use of magnetic waves to make pictures of the inside of the body. Using a large magnet, radio waves, and a computer, an MRI produces two-dimensional and three-dimensional pictures.
PARTS OF THE BODY INVOLVED
An MRI can be used to evaluate any part of the body
REASONS FOR PROCEDURE
- To diagnose internal injuries or conditions
- To monitor effects of medications and treatments inside the body
RISK FACTORS FOR COMPLICATIONS DURING THE PROCEDURE
You may not be able to have an MRI exam if you have any of the following in your body:
- Ear implant
- Metal clips in your eyes
- Implanted port device
- Intrauterine device (IUD)
- Metal plate, pins, screws, or surgical staples
- Metal clips from aneurysm repair
- Retained bullets
- Any other large metal objects implanted in your body (tooth fillings and braces are usually not a problem)
You should tell the doctor/technician if your occupation involves work with metal filings or particles.
WHAT TO EXPECT
Prior to Procedure
- In the days leading up to your MRI exam:
- You may be asked to avoid using hair gel, spray, lotions, powders, and cosmetics before your MRI
- If your doctor prescribes a sedative:
- Arrange for a ride to and from the exam
- Do not eat or drink at least 4 hours before the exam
- Take it 1-2 hours before the exam, or as directed
- If you have not been prescribed a sedative, eat or drink normally, unless your doctor or the technician tells you otherwise
Once at the MRI center:
You will be asked about the following:
- Medical history
- Pregnancy, if female
- Prior head surgery
- You'll remove any metal containing objects, such as jewelry, hairpins, hearing aids, glasses, wigs (with metal clips), and/or nonpermanent dentures
- An x-ray may be taken beforehand if there is doubt as to whether there are metal objects in your body
- You'll also remove all objects from your pockets or change into a hospital gown
- You may be given ear plugs or stereo headphones to wear, due to the loud banging noise the MRI machine makes during the exam
- You may receive an injection of contrast imaging dye
- Often, a family member or friend will be allowed to remain in the MRI examining room with you
Anesthesia – None, unless you are claustrophobic, in which case your doctor can prescribe a sedative (such as Valium) to take before the exam.
Description of the Procedure - You lie very still on a sliding table. Depending on your medical condition, you may have monitors placed to keep track of pulse, heart rate, breathing, etc. The table is slid into the MRI's narrow, enclosed cylinder (unless it is an "Open" MRI). The MRI technician leaves the room, and each of the MRI sequences is performed. The technician gives you any necessary directions, such as to hold your breath momentarily, via the intercom. You are able to talk to the technician through this intercom as well.
If a contrasting dye (usually Gadolinium) is needed, a small IV needle is inserted into your hand or arm before you are slid into the MRI machine. First, a saline solution is dripped into your vein to prevent clotting. Then, usually two-thirds of the way through the exam, the contrasting agent is injected.
When the MRI exam is completed, you are slid out of the machine, the IV needle is removed, and you are asked to dress and wait in the waiting room until MRI images can be checked to be sure no additional images are necessary.
After Procedure – You will be asked to wait until MRI images are examined to determine if more images are needed. If so, more images will be taken at that time.
How Long Will It Take? 40-90 minutes
Will It Hurt? The MRI exam is painless. If you have a contrast dye injected, there may be a momentary stinging when the IV needle is inserted, and you may also feel a slight cooling sensation as the dye is injected.
If you are claustrophobic, you may find this exam very difficult. A conventional MRI machine is a very small, enclosed cylindrical tube, and you need to lie very still in it for an extended period of time. However, you can ask your doctor to prescribe a sedative for the exam. Also, ask your doctor about having the exam done in an "Open" MRI machine, which is much larger then a conventional MRI and is usually open on the sides and in the front and back.
Possible Complications – Allergic reaction to contrasting dye, if used (rare)
Average Hospital Stay – None
- If you took a sedative, do not drive, operate machinery, or make important decisions until the sedative wears off completely
- If you are breastfeeding and receive a contrasting dye injection during the MRI exam, wait at least 24 hours after the exam before breastfeeding again, unless told otherwise by your doctor
After the exam, an MRI radiologist will analyze the images and send a report to your doctor. Your doctor will discuss the results and any further action, tests, or treatment that may be necessary with you.
CALL YOUR DOCTOR IF ANY OF THE FOLLOWING OCCURS
- Any allergic or abnormal symptoms after an exam in which you were injected with contrasting dye
- Worsening of any of the symptoms that prompted the MRI exam
University of Iowa Radiology Department
"How Magnetic Resonance Imaging (MRI) Works," by Todd A. Gould, Registered Technologist in Radiology and Magnetic Resonance Imaging with the American Registry of Radiologic Technologists