Magnetic resonance imaging (MRI) is a noninvasive procedure that allows physicians to observe the inner workings of the human body. In an MRI test, a magnetic field and pulses of radio waves are used to generate cross-sectional images of organs, bone, soft tissue, and almost every other internal body structure.
Unlike computed tomography and traditional x-ray imaging tests, MRI does not use ionizing radiation to take pictures. An MRI machine uses produces a magnetic field that is 10 times stronger than Earth’s to generate its images. When the magnetic field interacts with the human body, it forces the body’s hydrogen atoms to “line up” in similar formation. Radio waves are then sent toward the hydrogen atoms. The hydrogen atoms reflect the radio waves, which are analyzed by a computer (similar to SONAR technology) to create a cross-sectional picture of the human body.
How is MRI Used to Diagnose and Treat Cancer?
Magnetic resonance imaging can help physicians assess the following:
- Is a tumor present somewhere in the body?
- What is the size, shape, and location of the tumor?
- Where should incisions and/or certain instruments be located in the event of surgery or other invasive procedures?
- What is the best treatment strategy to rid the body of cancer and/or help the patient cope with symptoms?
- Following treatment, how has the cancer responded to medication, surgery, therapies, and other treatment modalities?
How is the Test Performed?
The patient will be asked to wear a hospital gown and remove any metal accessories from the body. Metal causes the magnetic field to produce inaccurate images. Next, the patient will lie on a narrow examination table, which slides into the MRI machine. Straps and bolsters are commonly used to help the patient maintain the correct imaging position.
In some cases, contrast dies are used to illuminate certain structures in the body. These dies may be injected directly into the bloodstream with a needle and syringe or they may be swallowed, depending on the area of the body being studied.
Once the exam is finished, the patient may be asked to remain in the machine until the technologists confirms that the images are accurate.
Duration: An MRI test typically involves capturing several images. Each image may take up to 15 minutes to capture. As a result, an MRI may 45 minutes or longer to complete.
Preparing for an MRI
Patients are frequently asked to fast 4 to 6 hours before the test. Depending on the part of the body being studied, this will result in a clearer image. Other preparations are not needed.
The magnetic field produced by an MRI machine may interact negatively with certain substances and devices:
- Brain Aneurysm Clips
- Inner Ear (Cochlear) Implants
- Recently Placed Artificial Joints
- Certain Implants, such as Pacemakers
- Certain Types of Vascular Stents
If you have any of the aforementioned devices in your body, you consult your doctor before having an MRI test. Furthermore, people exposed to small fragments of metal in the workplace should have skull x-ray performed before receiving MRI. A skull x-ray will be used to check for metal fragments in the eyes and ears, which may interact negatively with the MRI’s magnetic field.
What to Expect
MRI tests are painless. Some patients report feelings of mild to severe anxiety and/or restlessness during the test. If you are claustrophobic, or if it is difficult for you to lie still for long periods of time, you may be given a mild sedative before the test.
MRI machines produce loud banging, thumping, and humming sounds. Wear earplugs to reduce the noise.
“Recovery time” does not apply to an MRI test. Once the procedure is complete, you can resume your normal daily activities, dietary habits, medications, and sleep routine.
Why is an MRI Performed?
Magnetic resonance imaging is used to locate tumors, bleeding sites, blood vessel diseases, and infections. An MRI test may be recommended in addition to a CAT scan, ultrasound, or x-ray in order provide a more complete picture of internal body structures.
To diagnose cancer, magnetic resonance imaging may be used to observe tumors in the head, chest, blood vessels, abdomen, pelvis, bones and joints, and spine. If a tumor is detected, additional MRI tests may be recommended to observe the tumor’s growth and response to treatment.
References
- Radiological Society of North America, Inc. (RSNA). 2009. Retrieved on April 20, 2009 from.
- Healthwise, Inc. Family of Sites. 1995-2008. Retrieved on April 20, 2009 from.
- A.D.A.M., Inc. Family of Sites. 1997-2009. Retrieved on April 20, 2009 from.
