Magnetic Resonance Imaging (MRI)

Magnetic Resonance Imaging (MRI) - Head

• What is MRI of the Head?
• What are some common uses for MRI of the Head?
• How is the scan performed?
• Who interprets the MRI scan and how do I get them?
• What are the limitations of MRI of the Head?
• What are the benefits vs. risks?

What is MRI of the Head?

Magnetic resonance imaging (MRI) uses radio waves and a magnetic field rather than x-rays to provide remarkably clear and detailed pictures of internal organs and tissues. This technique has proved very helpful to radiologists in diagnosing tumors of the brain as well as disorders of the eyes and the inner ear. It requires specialized equipment and expertise and allows evaluation of some body structures that may not be as visible with other imaging methods.

What are some common uses for MRI of the Head?

MRI is the most sensitive exam for brain tumors, strokes and certain chronic disorders of the nervous system such as multiple sclerosis. Current MRI systems can depict brain function, and in this way detect a stroke at a very early stage. In addition, it is a useful means of documenting brain abnormalities in patients with dementia and it is commonly used for patients with disease of the pituitary gland. MRI can detect tiny areas of tissue abnormality in patients with disease of the eyes or the inner ear.

How is the scan performed?

The patient is placed on a sliding table and a radio antenna device called a surface coil is positioned around the upper part of the head. After positioning the patient with the head inside the MRI gantry, the technologist leaves the room and the individual MRI sequences are performed. The patient is able to communicate with the technologist at any time using an intercom. Also, many MRI centers allow a friend or, if a child is being examined, a parent into the room. Depending on how many images are needed, the exam will generally take 15 to 45 minutes, although a very detailed study may take longer. During imaging, you will be instructed not to move. You will know when images are being recorded because you will hear tapping or thumping sounds when the coils that create the magnetic field are turned on. In between sequences, you will be able to relax. Patients are generally required to remain still for only a few minutes at a time. Some patients will require an injection of a contrast material to enhance the visibility of certain tissues or blood vessels. The contrast material is injected about two-thirds of the way through the exam. A small needle connected to an intravenous line is placed in an arm or hand vein for the injection.

When your exam is completed, you will wait a short time on the table while the images are examined to ensure no additional images are needed.

Who interprets the MRI scan and how do I get them?

A neuroradiologist, who is a physician experienced in head, neck and spine MRI examinations, will analyze the images and send a signed report with his or her interpretation to the patient's personal physician. A preliminary interpretation may be available shortly after the exam and a formal report of the complete results will be sent to the referring physician within a day. Your primary physician or the radiologist may discuss the findings of the MRI examination with you. New technology also allows for distribution of diagnostic reports and referral images over the Internet to our facility.

What are the limitations of MRI of the Head?

Bone is better imaged by conventional x-rays, and CT is preferred for patients with severe bleeding, acute trauma or who because of their medical condition are unable to tolerate an MR scan procedure. MRI may not always distinguish between tumor tissue and edema fluid and does not detect calcium when this is present within a tumor. In most cases the exam is safe for patients with metal implants but there are a few exceptions, so patients should inform the technician of an implant prior to the test. The exam must be used cautiously in early pregnancy. MRI often costs more than CT scanning.

What are the benefits vs. risks?

Benefits:

• Images of the brain, spine, joints and soft tissue structures are clearer and more detailed than with other imaging methods.

• MRI contrast material is less likely to produce an allergic reaction than the iodine-based materials used for conventional x-rays and CT scanning.

• Exposure to radiation is avoided.

• MRI enables the detection of abnormalities that might be obscured by bone tissue with other imaging methods.

• MRI provides a fast, noninvasive alternative to x-ray angiography for diagnosing problems of the vessels of the head and neck. A variant called MR angiography (MRA) provides detailed images of blood vessels in the brain and other body parts- oftentimes without the need for contrast material. The risk of an allergic reaction from MRA contrast is extremely low and kidney damage does not occur.

• New MRI systems can depict brain function, and in this way detects a stroke at a very early stage.

Risks:

• There are no definite side effects from any type of MRI study, including MR angiography.

• An undetected metal implant may be affected by the magnetic field. The procedure should be avoided in any patient with a pacemaker, implanted neurostimulator, certain types of metallic ear implants(cochlear implants) or metallic object within the eye socket. It should also be avoided if the patient has a port for delivering insulin or chemotherapy (however, many ports are detachable so patients can safely undergo MRI examinations).

• MRI is generally avoided in the first 12 weeks of pregnancy. Doctors usually use other methods of imaging, such as ultrasound, on pregnant women unless there is a strong medical reason.

• Women who are breast-feeding should inform the radiologist and ask how to proceed. If necessary they may pump breast milk before the exam for use until the gadolinium contrast material has cleared from the body.

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