CT scan

The computed tomography (CT) scan is a medical imaging procedure that uses x-rays and digital computer technology to create detailed two or three-dimensional images. Unlike other forms of medical imaging, the CT scan can image every type of body structure at once including bone, blood vessels and soft tissue.

The equipment consists of a large square machine with a circular hole. Inside the machine is a rotating gantry that carries the x-ray source and electronic x-ray detectors. An attached table slides the reclining person into the hole.

Multiple x-rays are taken in thin cross-sections along the person’s body (imagine a loaf of sliced bread). The detectors collect the x-ray information from each cross-section and send them to a special computer that combines them into a single image.

The CT scan may also be referred to by its older name of computed axial tomography or ‘CAT’ scan.

When a CT scan is used

Some of the common uses of the CT scan include:

• Assessment of a body part’s structure or shape
• Diagnosis of disease, particularly cancer
• Diagnosis of trauma or injury
• Diagnosis of vascular disease
• Aid to planning particular surgeries
• Aid to planning radiotherapy
• Visual aid to radiotherapy administration
• Visual aid to certain surgical procedures such as biopsy or needle aspiration
• Measurement of bone strength
• Alternative to some types of exploratory or diagnostic surgery.

Medical issues to consider

Medical considerations prior to the CT scan may include:

• Tell the doctor if you are pregnant or think you may be pregnant. Another type of test may be recommended.
• Tell the doctor if you have allergies, diabetes or renal impairment.
• Tell the doctor if you experience claustrophobia. The doctor may give you mild sedatives to help you relax during the procedure.
• Tell the doctor about any implanted device you may have such as a pacemaker or medication pump, as metal objects may distort the images.
• Follow all the instructions you are given. Some CT scans require the use of contrast material to improve the image quality. The contrast material may be taken orally or by an intravenous injection (or both).
• You may have to go without food and drink for a certain length of time before the procedure. Your doctor will give you detailed instructions on how to prepare for the test and what to expect.
• A very obese person may be too big for the circular hole of the CT machine. The doctor may advise another type of medical imaging or diagnostic test.

CT scan procedure

Generally, the procedure includes:

• You may be given a large drink to consume before the procedure. This drink is a contrast agent that helps to enhance pictures of the stomach, small intestines and bowel. In some cases, the contrast agent is administered as an enema.
• You will be asked to undress and wear a hospital gown. You must remove all metal objects including jewellery and wristwatch.
• You lie down on the scanner table. The radiographer may use straps and foam pillows to position your body and help keep you still.
• You may be given an intravenous injection of an iodinated contrast medium (a type of dye) to help produce better images. This substance may cause a strange warm feeling that lasts for a few seconds, a funny metallic taste in the mouth or the sensation that you have ‘wet’ yourself.
• The table slides into the circular hole in the machine.
• Depending on the body part and particular condition being investigated, a number of images may be taken as the table edges forward.
• The gantry moves in a circle around you as it takes the x-ray images. Each revolution (turning) of the gantry takes less than a second and there may be a number of revolutions depending on the examination.
• Lie very still. This is very important, as movement will blur the images. You may be asked to hold your breath for a few seconds while the gantry rotates.
• The equipment makes noises such as clicks and buzzes while taking the images. Don’t be alarmed – this is normal.
• Depending on the nature of the medical investigation, the CT scan may take anywhere from a few minutes to half an hour or more.

Immediately after the CT scan

You may be asked to wait while the radiographer reviews the images. In some cases, more images must be taken. Once they are deemed satisfactory, you can dress and leave. The medically qualified radiologist assesses the scans. The results are usually sent to your referring doctor so you will need to make a follow-up appointment.

Complications of a CT scan

The CT scan is a very safe procedure. Some people who have an injection of iodinated contrast material may feel nauseous for a short time afterwards. On rare occasions, a person may have an allergic reaction to this substance.

Taking care of yourself at home

The CT scan is a non-invasive, painless and relatively safe procedure that doesn’t require any recovery time. Be guided by your doctor but, generally speaking, you can resume normal activities as soon as you leave.

Breastfeeding after a CT scan

Nursing mothers should avoid breastfeeding for about 24 hours after a CT scan that requires the use of medium. This is because some of the ingredients in the dye that is used can pass into your breast milk and may be passed on to your baby. Tell your doctor or radiologist that you are breastfeeding before your CT scan and ask about what they recommend for you.

Long-term outlook

There are no known long-term side effects from having a CT scan. However, the procedure is thought to very slightly increase a person’s chance of developing cancer. To keep this small risk in perspective, a typical CT scan will expose you to the same amount of radiation that you would receive from the general environment over about three years.

Alternatives to a CT scan

Alternatives to a CT scan depend on the medical condition under investigation, but could include:

• MRI scan
• Ultrasound
• Blood test
• Biopsy
• Exploratory surgery.

Where to get help

• Your doctor
• Radiographer
• Radiologist

Things to remember

• The CT scan is a medical imaging procedure that uses x-rays and digital computer technology to create detailed pictures of the body.
• It can image every type of body structure at once including bone, blood vessels and soft tissue.
• The CT scan is a non-invasive, painless and relatively safe procedure that doesn’t require any recovery time.

You might also be interested in:

• MRI scan.
  
• PET scan.
  
• Ultrasound scan.
  
• X-ray examinations.
  

Want to know more?

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This page has been produced in consultation with and approved by:

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Monash University - Department of Medical Imaging and Radiation Sciences

Last reviewed: November 2011

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The computed tomography (CT) scan is a medical imaging procedure that uses x-rays and digital computer technology to create cross-section images of the body. It can image every type of body structure at once including bone, blood vessels and soft tissue. The CT scan may also be referred to by its older name of computer assisted tomography or 'CAT' scan.

Content on this website is provided for education and information purposes only. Information about a therapy, service, product or treatment does not imply endorsement and is not intended to replace advice from your qualified health professional. Content has been prepared for Victorian residence and wider Australian audiences, and was accurate at the time of publication. Readers should note that over time currency and completeness of the information may change. All users are urged to always seek advice from a qualified health care professional for diagnosis and answers to their medical questions.

For the latest updates and more information, visit www.betterhealth.vic.gov.au

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