Alternative Names MRI, head, MRI, cranial, cranial magnetic resonance imaging, magnetic resonance imaging, cranial, magnetic resonance imaging, head
Definition Magnetic resonance imaging (MRI) is a noninvasive imaging technique. It is used to view organs, soft-tissue, bone, and other internal body structures. In a cranial MRI, the person's head is exposed to radio waves while in a magnetic field. A cross-sectional picture of the skull and brain is produced by energy emitted from hydrogen atoms in the body's cells. An individual is not exposed to radiation during this test.
Who is a candidate for the test? A cranial MRI can be used for a variety of purposes. It is the most sensitive type of examination for identifying:
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 examination. 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.
What is involved in preparation for the test? Before the test, the person is asked to remove all metal objects that might affect imaging. These items include jewellery, hearing aids, hairpins, eyeglasses and removable dental work. Also, the person should inform the MRI technologist about any previous surgery, which required placement of metal, such as a hip pinning. Internal metal objects that cannot be removed may distort the final images. Since the magnetic field can damage watches and credit cards, these objects are not taken into the MRI scanner. Food and fluid restrictions are not required before an MRI.
What do the test results mean? A special doctor called a radiologist analyses the MRI images. Cranial MRIs can reveal the size and location of tumours, blood vessel abnormalities, haemorrhages and other soft-tissue problems. MRI is useful in evaluating bony disorders that affect the skull. The patient's doctor and the radiologist will use this information to help guide the next course of action for the individual's condition.
Author: Stephanie Slon, BA Reviewer: HealthAnswers Australia Medical Review Panel Editor: Dr David Taylor, Chief Medical Officer HealthAnswers Australia Last Updated: 1/10/2001 Contributors Potential conflict of interest information for reviewers available on request
