Alternate Names : Magnetic Resonance Imaging, Nuclear Magnetic Resonance Imaging (NMRI)
Magnetic resonance imaging (MRI) is a noninvasive imaging technique. This special machine is used to view organs, bone and other internal body structures.
The imaged body part is exposed to radio waves while in a magnetic field. The picture is produced by energy emitted from hydrogen atoms in the human body. An individual is not exposed to radiation during this test.
Who is a candidate for the test?
MRI can be used for a variety of purposes. A MRI of the brain, known as a cranial MRI, may be ordered by a healthcare provider to evaluate a person's tumor, seizure disorder or headache symptoms. A MRI of the spine may be requested to examine a disc problem in a person's spine. If an individual has sustained injury to the shoulder or knee, a MRI is frequently used to study these large joints. Disease of the heart, chest, abdomen and pelvis are also commonly evaluated with MRI.
How is the test performed?
Before the test, the doctor will ask if the person:
has any drug allergies, or history of allergic reaction to medications
is allergic to shellfish, or foods with added iodine such as table salt
has experienced claustrophobia, or anxiety in enclosed spaces. If this is a problem, mild sedating medication may be given.
A woman will also be asked if she might be pregnant.
As the test begins, the person lies on a flat platform. The platform then slides into a doughnut-shaped magnet where the scanning takes place. To prevent image distortion on the final images, the person must lie very still for the duration of the test.
Commonly, a special substance called a contrast agent is administered prior to or during the test. The contrast agent is used to enhance internal structures and improve image quality. Typically, this material is injected into a vein in the arm.
The scanning process is painless. However, the part of the body being imaged may feel a bit warm. This sensation is harmless and normal. Loud banging and knocking noises are heard by the person during many stages of the exam. Earplugs are provided for people who find the noises disturbing.
After the test, the person is asked to wait until the images are viewed to see if more images are needed. If the pictures look satisfactory, the person is allowed to leave.