A magnetic resonance imaging (MRI) scan is a noninvasive test that uses magnets and radio waves to create images of the inside of your body. It allows doctors to see details of your organs and tissues without having to make any incisions.
According to the Mayo Clinic, the magnetic field created by an MRI temporarily aligns the water molecules in your body. The radio waves take these aligned particles and make them produce faint signals, which are recorded by the machine and rendered as images.
Unlike X-rays and CT scans, an MRI does not use radiation. It is considered a safer alternative test, especially for pregnant women.
Your doctor may order an MRI if he or she needs to take a closer look at the vessels, tissues, and organs of your body. According to the Radiological Society of North America, various medical conditions could require this. (RSNA) They include:
- problems with your organs or blood vessels, or within your chest, abdomen, or pelvic region
- lumps in the breasts
- problems with your reproductive system
- heart problems
- cysts in the urinary tract
- birth defects
- blockages or variations in the structure of blood vessels
The test can be used to evaluate problems in the brain, such as bleeding, tumors, and structural damage. During pregnancy, it is sometimes used to monitor the health of the fetus.
Your doctor will explain why he or she believes an MRI is required before you have the test.
Since the test does not use radiation, there are few risks from an MRI scan. To date, there have been no documented side effects of the radio waves and magnets used in the scan.
However, be sure to notify your doctor before your scan if you have a pacemaker or metal implants from previous surgeries or injuries. The magnets used can affect these devices. Common metal implants include:
- artificial joints
- artificial heart valves
- metal clips from an aneurysm surgery
- bullets or other metal fragments
Rarely, a person will have allergic reaction to the contrast dye used during an MRI. The Radiology Society of North America warns mothers not to breastfeed their children for 24 to 48 hours after they have been given contrast dye during an MRI.
If you are claustrophobic, or have a hard time in enclosed spaces, you may feel uncomfortable while in the MRI machine. However, there is nothing to fear. Talk to your doctor about your concerns before the test. He or she may be able to prescribe an antianxiety medication to help with your discomfort. In some cases, patients can be sedated during the process.
Preparations for an MRI vary among testing facilities. Your doctor or the attending technician will give you complete instructions about how to prepare for the test.
Before the MRI, your doctor will explain the test and take a complete medical history. Be sure to tell your doctor about any medication you are taking, including over-the-counter drugs and herbal supplements, or any known allergies.
If you have a pacemaker, your doctor may suggest another method for evaluating your condition, such as a CT scan. However, some pacemaker models can be reprogrammed before an MRI so that they are not disrupted during the examination.
Because the MRI uses magnets, you’ll also need to remove any metal from your body, including jewelry, body piercings, and zippers. You will also be asked to change into a hospital gown before your MRI.
Your MRI may involve the use of a special dye to highlight an area of concern. This dye—called gadolinium — is administered through an IV. While allergic reactions to the dye are rare, alert your doctor of any concerns before the dye is injected.
Other preparations may be required, depending on the area of the body being examined. For instance, if you doctor is inspecting your intestines, you may need to clear your bowels. This will require you to use laxatives or an enema. You also may need to fast for four to six hours before the exam.
You will first be positioned on a bench so that the correct area of your body can be scanned. You may be given a pillow or blanket if the bench in uncomfortable for you.
If your test requires contrast dye, it will be injected via an IV. You may have to wait for about an hour for the dye to work its way through your bloodstream and reach the area being examined.
A technician will control the movement of the bench using a remote control from another room. He or she will be able to communicate with you through a microphone.
You will slide into the machine, and it will make loud noises as the images are taken. Many hospitals offer earplugs, and others have televisions or headphones to help you pass the time.
As the pictures are being taken, the technician will ask you to hold your breath for a few seconds. Remember, you will not feel anything during the test, since the magnets and radio frequencies—those similar to FM radios—cannot be felt.
During some MRIs, you will have to perform small tasks or answer questions. These are called functional MRIs, and they allow the technician to pinpoint the parts of your brain responsible for these actions.
The whole MRI process typically takes about an hour.
If the MRI images are projected onto film, it can take hours to get the film developed. It will also take time for your doctor to review the images and interpret them. Many machines display images on a computer, allowing your doctor to view them more quickly.
Preliminary results from an MRI may arrive within a few days, but comprehensive results can take up to a week or more. Your doctor will fully explain the results when the images are complete.