A special dye, called contrast, may be injected into your hand or forearm before the test starts. Contrast can highlight specific areas inside the body, which creates a clearer image.
You will be asked to lie on your back a narrow table that slides into the center of the CT scanner. Only your head is positioned inside the CT scanner.
You may be allowed to rest your head on a pillow, but this must be done before the scan begins. It is very important that once your head is in place, you do not move it during the test. Movement causes blurred images.
Once inside the scanner, the machine's x-ray beam rotates around you. (Modern "spiral" scanners can perform the exam in one continuous motion.)
Small detectors inside the scanner measure the amount of x-rays that make it through the part of the body being studied. A computer takes this information and uses it to create several individual images, called slices. These images can be stored, viewed on a monitor, or printed on film. Three-dimensional models of organs can be created by stacking the individual slices together.
Generally, complete scans take only a few minutes.
You must sign an informed consent form. Remove dentures, any jewelry, and anything metal.
If contrast is used, you may be asked not to eat or drink anything for 4-6 hours before the test.
Some people have allergies to IV contrast and may need to take medications before their test in order to safely receive this substance.
Some people may have discomfort from lying on the hard table.
Contrast given through an IV may cause a slight burning sensation, a metallic taste in the mouth, and a warm flushing of the body. These sensations are normal and usually go away within a few seconds.
This test is helpful for diagnosing diseases that affect the following areas:
- Blood vessels
- Eye muscles
- Nerves supplying the eyes (optic nerves)
An orbit CT scan may also be used to detect:
- Abscess (infection) of the eye area
- Hard-to-see fractures of the eye socket
- Foreign object in the eye socket
CT scans and other x-rays are strictly monitored and controlled to make sure they use the least amount of radiation. The risk associated with any individual scan is small. The risk increases as numerous additional studies are performed.
In some cases, a CT scan may still be done if the benefits greatly out weigh the risks. For example, it can be more risky not to have the exam, especially if your health care provider thinks you might have cancer.
The most common type of contrast given into a vein contains iodine. If a person with an iodine allergy is given this type of contrast, nausea, sneezing, vomiting, itching, or hives may occur.
If you absolutely must be given such contrast, your doctor may choose to treat you with antihistamines (such as Benadryl) or steroids before the test.
The kidneys help filter the iodine out of the body. Therefore, those with kidney disease or diabetes should receive plenty of fluids after the test, and be closely monitored for kidney problems. If you have diabetes or are on kidney dialysis, talk to your health care provider before the test about your risks.
Rarely, the dye may cause a life-threatening allergic response called anaphylaxis. If you have any trouble breathing during the test, you should notify the scanner operator immediately. Scanners come with an intercom and speakers, so the operator can hear you at all times.