Rabies risks and causes


Certain imaging tests can aid in the diagnosis of rabies encephalitis (i.e., acute inflammation of the brain resulting from rabies infection). These imaging tests include head MRIs and head CT scans.

Head MRIs

“MRI” stands for “magnetic resonance imaging,” a procedure that involves using magnets and radio waves to create detailed pictures of your brain and the nerve tissues surrounding it.

Before undergoing a head MRI, you may be given a special dye (called “contrast material”), which helps improve image clarity for the radiologist. This dye is generally administered intravenously through the hand or forearm. Although the dye is very safe, some people may experience allergic reactions. What’s more, the most common type of dye (gadolinium) may be harmful to people with kidney problems.

Usually performed at a hospital or radiology center, head MRIs typically last 30 to 60 minutes. The procedure causes no pain and there’s no recovery time.

During an MRI, you’ll lie on a narrow table, which then slides into a tunnel-shaped scanner. If you’re claustrophobic or uncomfortable in close spaces, tell your healthcare provider before undergoing a head MRI. Medication may help to alleviate your anxiety during the procedure.

You should also tell your healthcare provider if you have:

  • brain aneurysm clips
  • artificial heart valves
  • a heart defibrillator or pacemaker
  • inner ear (cochlear) implants
  • kidney disease or dialysis
  • a recently placed artificial joint
  • a blood vessel stent
  • an allergy to iodine, which is used in the contrast material

In addition, make sure to let your healthcare provider know if you’ve worked with sheet metal in the past.

To prepare for your head MRI, you’ll most likely be asked not to eat or drink anything for 4 to 6 hours beforehand. However, you can go back to your normal diet, activity, and medication use immediately after the test.

Head CT Scans

In a head computed tomography (CT) scan, X-rays are used to create pictures of your head. Like head MRIs, head CT scans are performed at hospitals and at radiology centers.

When undergoing a head CT scan, you’ll lie on a narrow table that slides into the center of a CT scanner. While you’re inside the scanner, the machine’s X-ray beam will rotate around you. The complete scan typically takes somewhere between 30 seconds and a few minutes.

As with some head MRIs, certain CT exams require the use of a special dye delivered intravenously through the hand or forearm. Before receiving the dye, tell your healthcare provider if you have kidney problems or take the diabetes medicine metformin.

Although head CT scans are painless, the contrast material may trigger several side effects, including: 

  • a slight burning feeling.
  • a metallic taste in the mouth.
  • warm flushing of the body.

In rare cases, the dye may cause anaphylaxis (a life-threatening allergic response). If you experience any trouble breathing during the test, alert the scanner operator immediately. Tell a healthcare provider if you have any metal in or on your body, and do not enter an MRI room with anything metal.

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