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CT (computed tomography) scan

Matawai irirangi ā-rorohiko

A CT (computed tomography) scan is a type of scan that uses X-rays to take detailed pictures in very fine slices through the part of your body being investigated.

The pictures are processed by a computer to create cross-sectional images of your soft tissues and bones.

Most scans only take 20 to 30 minutes.

Before Your Scan

Often, you will not need to do anything to prepare for your scan. But for some scans, you'll need to fast (not eat or drink) before your appointment. Fasting for two to four hours is common, but you can usually drink water over this time to avoid dehydration (losing too much water from your body).

You'll be given instructions on what you need to do when you receive your appointment letter.

If you're pregnant, or think you may be pregnant, discuss this with your doctor and the CT staff.

During your scan

You'll be asked to lie on a motorised table. The table will slide through the opening of the scanner, which is shaped like a large ring. The ring contains an X-ray tube and detectors that will rotate around you. You'll hear a whirring noise as they rotate.

The person doing the scan will be able to see and hear you at all times and you'll be able to communicate with them through an intercom. It's important to stay as still as you can throughout the scan.

Sometimes, you'll need an injection or drink of contrast dye. This is an iodine solution that helps highlight some of your body's internal structures. It's usually injected into your arm, and you may feel a warm flush through your body during the injection.

After your scan

A specialist doctor (radiologist) will view the images and write a report about what the scan shows. They will send their report to the health professional who asked for the test, who will then discuss the test results with you during a follow-up appointment, over the phone or by email or text message.

Risks of the scan

A CT scan uses a small amount of radiation. It's greater than the amount you would get during a simple X-ray but it's still a small amount. The low dose of radiation you're exposed to during a CT scan has not been shown to cause harm. You can read more detailed information about radiation risk.

If you need a contrast dye injection, a small plastic tube will be put in a vein in your arm. There is a small chance of an allergic reaction. This is usually mild, but if you have a more severe reaction, the CT staff will treat it.

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Written by HealthInfo clinical advisers. Last reviewed December 2022.

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