What is a CT scan (computed tomography)?
In conventional x-rays, a beam of energy is aimed at the body part being studied. A plate behind the body part captures the variations of the energy beam after it passes through skin, bone, muscle, and other tissue. While much information can be obtained from a regular x-ray, specific detail about internal organs and other structures is not available.

With computed tomography scan (also called CT or CAT scan), the x-ray beam moves in a circle around the body. This allows for many different views of the same organ or structure, and provides much greater detail. The x-ray information is sent to a computer which interprets the x-ray data and displays it in two-dimensional form on a monitor.

CT scans may be done with or without contrast. "Contrast" refers to a substance taken by mouth or injected into an intravenous (IV) line that causes the particular organ or tissue being studied to be seen more clearly.

What is the preparation for a CT scan?
If your physician schedules a CT scan of the heart or chest and decides to use contrast dye, you may need to be fasting, nothing by mouth, for a period of time prior to the procedure. You will receive instructions about this from your physician or another healthcare professional.

You will need to let your physician know if you have ever had a reaction to any contrast dye, or if you are allergic to iodine. The risk of a serious allergic reaction to contrast materials containing iodine is rare, and radiology departments are equipped to handle them. A reported seafood allergy is not considered to be a contraindication for iodinated contrast. If you are pregnant or could be pregnant, you should notify the physician prior to the procedure.

You may receive a mild sedative before the procedure to make you feel more comfortable, and to help you to remain still and quiet during the procedure, which may last 30 to 60 minutes.

How is the CT scan performed?
The CT scanner is located in a large room. You will lie on a narrow table that slides into the hollow tube-shaped scanner.

You may have an intravenous (IV) line for contrast medication. The contrast medication may be injected prior to the procedure or during the procedure.

The CT physician and staff will be in an adjacent room where the equipment controls are located. However, they will be able to see you through a large window and will be monitoring you constantly during the procedure. If you are not sedated you will be given a call bell device to let the staff know if you need anything during the procedure. Speakers are located inside the scanner so that you can hear instructions from the CT staff and they can hear you respond.

Once the procedure begins, you will need to remain very still at all times so that movement will not adversely affect the quality of the images. At intervals, you will be instructed to hold your breath, if possible, for a few seconds. You will then be told when to breathe.

If the CT scan is being done "with and without contrast," you will receive contrast medication through an IV about halfway through the procedure. You may feel warm or flushed just after the dye goes into the vein - this is a normal feeling and it will go away shortly.

Once the procedure is finished, the table will slide out of the scanner. If you received medication for relaxation or sleep, you will be monitored until the medication wears off and you are awake again. If an IV was inserted, it will be taken out after the procedure is over and you are awake. 

You may be asked to wait for a short time while the radiologist reviews the scans to make sure they are clear and complete. If the scans are not sufficient to obtain adequate information, additional scanning may be done.

The test normally takes approximately 30 to 60 minutes.

What happens after the procedure?
Without sedation, you should be able to resume normal activities immediately, unless your physician instructs you otherwise.

With sedation, you may feel groggy, tired, or sleepy for a period of several hours after the procedure. However, the sedation effects should disappear within a day or so.

Depending on the results of the CT scan, additional tests or procedures may be scheduled, to gather further diagnostic information.