Brain and Spinal Cord Magnetic Resonance Imaging

Definition

Magnetic Resonance Imaging (MRI) is a diagnostic technique that provides high-quality cross-sectional images of organs and structures within the body, without X-rays or radiation.

It has special use in diagnosing disorders of the central nervous system (brain and spinal cord)(see Health Profile: MRI (Magnetic Resonance Imaging).

Description

The MRI image gives information about the chemical makeup of tissues, thus helping to distinguish normal, cancerous, atherosclerotic, and traumatized tissue masses in the image.

Evaluating Brain Tumors

MRI is the procedure of choice for the evaluation of neurologic dysfunction in a patient suspected of having cancer.

MRI and contrast-enhanced CT (computed tomography) scanning have now largely replaced the combination of skull X-ray, electroencephalogram, radionuclide brain scan, and arteriography as the principal tests for the evaluation of patients with suspected brain tumor.

MRI delineates most metastatic and primary tumors of the nervous system. In general, lesions (a wound, injury, or pathological change in body tissue) of the skull base and those in the brainstem, cerebellum, and spinal cord are visualized in greater detail with MRI than with CT, myelographic, or radionuclide images.

In addition to greater sensitivity and delineation of anatomic detail, MRI involves no radiation exposure. Paramagnetic contrast with intravenous gadolinium diethylene-triamine pentaacetic acid (gadolinium DTPA) produces contrast changes in MRI similar to those observed following the use of organic iodides in CT. The combination of paramagnetic agents and higher energy MRI units may provide better separation of tumor from non-tumor tissue and better resolution of the spinal cord and brachial plexus.

Gadolinium DTPA administration occasionally produces hypotension (low blood pressure), nausea or vomiting.

Magnetic resonance angiography (MRA) can also provide detailed information on the status of the intracranial (within the brain) circulation.

Diagnosing Multiple Sclerosis

The exquisite image contrast and spatial detail of MR images has led to its widespread use in patients with a variety of suspected neurological diseases, including Huntington's disease. One of the major uses of magnetic resonance imaging (MRI) has been in the diagnosis of multiple sclerosis (MS).

Multiple sclerosis is difficult to diagnose when patients with nonspecific neurological symptoms are seen early after their appearance. This, plus the fact that even the suspicion of MS is understandably worrisome to many patients, has frequently led physicians to suggest an MRI for patients with vague and nonspecific symptoms, as a means of establishing (or excluding) the diagnosis.

One review on the accuracy of MRI estimated that its sensitivity for MS was approximately 88 percent, with a false-positive rate of about 6 percent. MRI of the head is much more accurate than contrast-enhanced computed tomography (CT) for diagnosing MS.

In patients with objective neurological signs and a high likelihood of MS, MRI provides a fast, painless, and noninvasive way to confirm the diagnosis. However, MRI may not be especially sensitive for diagnosing MS in the absence of typical MS lesions. Therefore, clinicians and patients should not be reassured that a normal, unenhanced (no use of contrast dye to enhance the image) MRI necessarily excludes an MS diagnosis, especially if clinical symptoms of MS are present.

Risks

Despite the relative safety of MRI, two basic risks are associated with the procedure. The first risk relates to the immediate environment of the magnetic resonance imaging suite, where appliances and other magnetic materials may become high-speed projectiles in the presence of powerful magnetic forces.

The second risk involves patients who have metallic implants, including:

• Pacemakers

• Prosthetic cardiac valves

• Surgical clips

• Orthopedic appliances

• Penile implants

• Cochlear implants

• Intravascular filters

• Stents or coils

• Dental materials

• Shunt connectors

• Shrapnel

Questions to Ask Your Doctor

What is MRI and how does it work? How long does the test take?

Are there any risks or complications from the test?

Will Gadolinium DTPA or any other medium be administered? What are the side effects?

What happens if I feel claustrophobic or if I panic while in the tube?

How long does it take for the results?

What is the chance of a missed lesion or tumor? What is the chance of a false reading?