COMPUTED TOMOGRAPHY

Conventional X-ray Images

All x-ray imaging is based on the absorption of x rays as they pass through the different parts of a patient's body. Depending on the amount absorbed in a particular tissue such as muscle or lung, a different amount of x rays will pass through and exit the body. The amount of x rays absorbed contributes to the radiation dose to the patient. During conventional x-ray imaging, the exiting x rays interact with a detection device (x-ray film or other image receptor) and provide a 2-dimensional projection image of the tissues within the patient's body - an x-ray produced "photograph" called a "radiograph."

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Computed Tomography (CT)

Although also based on the variable absorption of x rays by different tissues, computed tomography (CT) imaging, also known as "CAT scanning" (Computerized Axial Tomography), provides a different form of imaging known as cross-sectional imaging. The origin of the word "tomography" is from the Greek word "tomos" meaning "slice" or "section" and "graphe" meaning "drawing." A CT imaging system produces cross-sectional images or "slices" of anatomy, like the slices in a loaf of bread. The cross-sectional images are used for a variety of diagnostic and therapeutic purposes.

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HOW A CT SYSTEM WORKS

A motorized table moves the patient through a circular opening in the CT imaging system.

As the patient passes through the CT imaging system, a source of x rays rotates around the inside of the circular opening.
The thickness of the fan beam may be as small as 1 millimeter or as large as 10 millimeters. In typical examinations there are several phases; each made up of 10 to 50 rotations of the x-ray tube around the patient in coordination with the table moving through the circular opening. The patient may receive an injection of a "contrast material" to facilitate visualization of vascular structure.

Detectors on the exit side of the patient record the x rays exiting the section of the patient's body being irradiated as an x-ray "snapshot" at one position (angle) of the source of x rays. Many different "snapshots" (angles) are collected during one complete rotation.

The data are sent to a computer to reconstruct all of the individual "snapshots" into a cross-sectional image (slice) of the internal organs and tissues for each complete rotation of the source of x rays.

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WHY THE TEST IS PERFORMED?

• Diagnose an infection
• Study blood vessels
• Identify masses and tumors (including cancer)
• Guide a surgeon to the right area during a biopsy

RISKS OF CT SCANS INCLUDE:

• Allergic reaction to contrast dye
• Being exposed to radiation

Some people have allergies to contrast dye.
The most common type of contrast given into a vein contains iodine. If you have an iodine allergy, type of contrast may cause nausea or vomiting,sneezing, itching,or hives.
If you absolutely must be given such contrast, your doctor may give you antihistamines or steroids before the test.
Your kidneys help remove iodine out of the body. You may need to receive extra fluids after the to help flush iodine out of the body if you have diabetes or kidney disease.

CT scans expose you to more radiation than regular x-rays. Having many x-rays or CT scans over time may increase your risk for cancer. However, the risk from any one scan is small.

CRANIAL CT SCAN

RECOMMENDED TO HELP DIAGNOSE OR MONITOR:

• Birth (congenital) defect of the head or brain
• Brain infection
• Brain tumor
• Buildup of fluid inside the skull (hydrocephalus)
• Craniosynostosis

RECOMMENDED TO HELP DIAGNOSE OR MONITOR:

• Injury to the head and face
• Stroke or bleeding in the brain

A CRANIAL CT MAY ALSO BE DONE IF THERE IS...

• Sudden changes in thinking or behavior
• Symptoms of damage to part of the brain(vision problems, muscle weakness, numbness, etc...
• Fainting