Magnetic resonance imaging (MRI), is a noninvasive imaging technique. It is used to view organs, soft tissue, bone, and other internal body structures.
A cranial MRI can be used for several reasons. It is the most sensitive type of exam to identify: brain tumorsbrain abscessesstrokesneurological diseases such as multiple sclerosisbrain abnormalities in people who have dementiadiseases of the pituitary glandabnormalities of the vision pathwayinner ear disorders
Before the test, the healthcare professional will ask if the person: has a pacemaker or any electronic device implantshas any mechanical heart valves or heart stentshas any history of brain surgery where a metal clip was placedhas any metal in the body (people who have had occupations cutting or grinding metal will require an X-ray to screen for small unknown particles of metal in the eyes)has any drug allergies or history of allergic reaction to medicineshas experienced claustrophobia, which is a fear of enclosed or small spaces. If this is a problem, mild sedating medicine 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 donut-shaped machine where the scanning takes place. To help keep the final images clear, the person must lie very still during the whole test.
A special substance called a contrast agent is often given before or during the test. The contrast agent is used to enhance internal structures and improve image quality. Typically, this agent is injected into a vein in the arm.
The scanning process is painless. However, the part of the body being imaged may feel somewhat warm. This feeling is harmless and is not a cause for concern. The person may hear loud banging and knocking noises during many stages of the exam. Earplugs are provided for people who are uncomfortable with the noises.
After the test, the person is asked to wait until the images are viewed to see if more pictures are needed. If they look satisfactory, the person can leave.
Before the test, the person is asked to remove all metal objects that might affect imaging. These items include jewelry, hearing aids, hairpins, eyeglasses, and removable dental work. Also, the person should inform the MRI technologist about any previous surgery that required placement of metal or electrical devices remaining in the body.
Internal metal objects that cannot be removed may make an MRI unsafe, because some metal implanted objects can be dislodged by the strong magnet used during the test. Electronic devices such as a cardiac pacemaker or defibrillator also make an MRI unsafe. In these people, other diagnostic tests must be used instead of MRI.
Since the magnetic field can damage watches and credit cards, these objects are not taken into the MRI scanner. Food and fluid do not need to be restricted before an MRI.
A special doctor called a radiologist analyzes the MRI images. The person's healthcare professional will consult with the radiologist regarding the next course of action based on the MRI findings.
Pagana, Kathleen D. and Timothy J. Pagana, Mosby's Manual of Diagnstic and Laboratory Tests, St. Louis, 1998.
"MR Imaging (MRI) - Head,"Radiological Society of North America (RSNA), 2000.