CT Scan: What to Expect and How to Prepare

CT stands for computed tomography. A CT scanner takes a series of X-ray measurements from many angles around your body, and a computer combines them into cross-sectional images — in effect, slices — that can also be reconstructed into three-dimensional pictures. You may hear it called a CAT scan.

The scanner is shaped like a large ring rather than a tunnel, so it is much more open than an MRI scanner. You lie on a table that moves through the ring while the images are taken.

A radiographer (also called a medical imaging technologist) carries out the scan. A radiologist — a specialist doctor — reads the images afterwards and writes a report for the doctor who referred you.

CT is fast and gives good detail of bone, blood vessels and many internal structures. Doctors commonly use it to:

• look for injuries after an accident
• examine the chest, abdomen and pelvis
• look at bones, including complex fractures
• examine blood vessels, usually with contrast
• investigate or monitor a known condition
• plan surgery or radiotherapy, or guide a biopsy

Which scan suits a particular question is a clinical decision, and it is made by weighing what the images would show against what the scan involves. If you are unsure why a CT was requested rather than another test, ask the doctor who referred you — that conversation is a normal part of the process, not a challenge to it.

Preparation depends on the part of the body being scanned and on whether contrast is planned, so the instructions the clinic gives you are the ones that apply. As a general guide:

• Ask when you book whether you need to fast, and from what time. Fasting is more often required when contrast is being given.
• Ask whether to take your usual medicines as normal, and mention every medicine you take — including those for diabetes.
• Ask whether you will need a recent blood test showing your kidney function, and arrange it early if so.
• Wear comfortable clothing without metal fastenings around the area being scanned. You may be asked to change into a gown.
• For some abdominal scans you may be given a drink to take before or on arrival; allow time for it.
• Allow more time than the scan itself takes — check-in, questions and cannulation happen first.

Tell the clinic when you book, not when you arrive. Several of the items below change what has to be arranged beforehand — a blood test, a different appointment time, or a different approach to contrast — and none of them can be organised at the front desk on the day.

None of these automatically means you cannot have a CT scan. They are the details the radiologist uses to decide how the scan should be done, whether contrast should be given, and whether anything should be arranged first.

Tell your doctor and the imaging clinic if you are pregnant or think you might be. Say so when you book and again when you arrive, even if it is already written on your referral.

This is not a reason to avoid contacting the clinic, and it does not necessarily mean the scan cannot go ahead. It may change which test is done, how it is done, or whether it is better to wait — and that is a decision for your doctor and the radiologist to make with you, once they know.

If you are breastfeeding, mention that too, particularly if contrast is planned, so the clinic can tell you what applies at that practice.

If there is any chance you could be pregnant and you are not sure, say so anyway. Being asked about the date of your last period, or being offered a pregnancy test, is a normal part of arranging imaging that uses X-rays.

• your referral, if it has not already been sent to the clinic
• your Medicare card, and any concession or DVA card
• private health insurance details, if the scan is being done as a private patient in hospital
• a list of your current medicines, including anything you take for diabetes
• a recent kidney function blood test result, if the clinic has asked for one
• any previous imaging or reports for the same problem, if you have them and they were done elsewhere
• details of any previous reaction to a contrast medium

1. You check in at reception and hand over your referral, along with your Medicare card and any concession card.
2. Staff go through your medical history, allergies, medicines, kidney function and the possibility of pregnancy.
3. You change into a gown if you have been asked to, and remove jewellery or clothing with metal near the area being scanned.
4. If contrast is planned, a small cannula (a thin plastic tube) is placed in a vein in your arm, and you may be asked to sign a consent form.
5. If you are having a drink of contrast for an abdominal scan, you take it and then wait for a period the staff will tell you about.

You lie on the scanner table, usually on your back, and the table moves slowly through the ring. The radiographer operates the scanner from an adjoining room, watching you through a window and speaking to you through an intercom.

CT is quiet compared with MRI — mostly a soft whirring. You will be asked to keep still, and for chest or abdominal scans you may be asked to hold your breath for a few seconds at a time. The actual image acquisition often takes only seconds.

If contrast is injected, many people feel a warm flush spreading through the body, a metallic taste, or a brief sensation of needing to pass urine. These are expected, pass within about half a minute, and are not a reaction. Tell the radiographer immediately if you feel itchy, short of breath, or unwell in any way.

Most CT appointments take around 10 to 30 minutes from the time you are called through, and most of that is preparation and positioning rather than scanning. The scan itself is often over in well under a minute.

Appointments involving contrast you drink take longer, because of the waiting period after you take it. Ask the clinic what to expect for your scan so you can plan the rest of your day.

The scan itself is not painful. You feel nothing from the X-rays, and nothing touches you while the images are taken.

If contrast is given by injection, you will feel the needle when the cannula goes in, much as you would for a blood test, and the warm flush described above. If lying flat or holding a position is painful for you, say so before the scan starts — it can often be made easier.

Many CT scans use a contrast medium, and many do not. Whether it is used depends on the clinical question your doctor is asking and on the scan protocol the radiologist chooses to answer it. The type used in CT is iodine-containing contrast medium.

It may be injected into a vein, swallowed as a drink, or occasionally given another way, depending on what needs to be seen. It leaves the body in your urine over the hours after the scan, and drinking normally afterwards helps that along unless you have been told to limit fluids.

Reactions are uncommon. Most are mild and settle by themselves; serious reactions are rare. Radiology practices and hospital imaging departments keep the medicines and equipment to treat a reaction on hand at all times, and staff are trained to use them.

You can ask why contrast has been recommended, and you can decline it. Declining may mean the scan answers less of the clinical question, so it is worth talking through with the staff at the time.

Yes. CT uses X-rays, which are a form of ionising radiation, and a CT scan generally involves a higher dose than a plain X-ray of the same area. This is worth understanding plainly rather than glossing over.

Everyone is exposed to ionising radiation continuously from natural sources — the ground, building materials, food and cosmic rays. In Australia that background exposure is estimated at around 2 millisieverts a year, roughly equivalent to 100 chest X-rays. A medical scan adds to that background exposure, and how much it adds depends on the scan.

At the doses used in medical imaging, exposure to ionising radiation is associated with a small increase in the lifetime risk of cancer. The increase is small, and it is generally smaller than the risk of a condition going undiagnosed or being treated on incomplete information. Children are more sensitive to radiation than adults, which is why scans for children are planned with particular care.

That balance is exactly why a CT scan is requested by a doctor rather than chosen from a menu: each scan is meant to be justified by what it will show. Once the scanner is switched off there is no radiation left in the room, and a CT scan does not make you radioactive.

If you would like to understand the balance for your own scan, the person to ask is the doctor who referred you. The radiologist at the imaging practice can also explain how the scan is planned to use the dose needed and no more.

A radiologist reviews your images and writes a report, which goes to the doctor who referred you. You are not usually given results at the clinic on the day, and the radiographer performing the scan will not interpret the images for you.

How long the report takes depends on the practice and on how urgent the scan is. Ask the clinic when the report is expected to be sent, then book a follow-up appointment with your referring doctor to go through what it means for you.

Most people go straight back to their usual activities. A CT scan does not make you radioactive, and there is no radiation left in your body once the scan is over.

If you had an injection of contrast, staff will usually ask you to wait a short while before leaving, remove the cannula, and suggest you drink normally over the rest of the day. Follow whatever they tell you about medicines and fluids — it is specific to you and it replaces any general advice here.

Contact your doctor if you feel unwell in the hours or days after the scan, including a rash or swelling. If you become seriously unwell — for example if you have difficulty breathing — seek urgent medical care. In an emergency, call 000.

In Australia, medical imaging is arranged through a referral (also called a request) from a doctor. You take that referral to an imaging provider, and for most types of imaging you may choose which provider you go to, unless your referral names one.

Whether a Medicare benefit applies to a particular scan, and how much of the fee it covers, depends on the item and on your circumstances. Some providers bulk bill some scans; others charge a fee, and you pay the difference between that fee and any Medicare benefit.

• Ask the imaging provider what the scan will cost you before you book, and whether they bulk bill it.
• Ask whether there is a separate charge if contrast is used.
• Services Australia publishes current information on Medicare and bulk billing, and MBS Online publishes the Medicare Benefits Schedule itself. Both are linked in the sources below.