CT Scan: What to Expect

What is a CT scan?

CT stands for computed tomography.

During a CT examination, an X-ray tube rotates around the body while detectors collect information from many different angles.

A computer then reconstructs this information into thin cross-sectional images.

Radiologists can review these images in different planes and can often reconstruct them into three-dimensional views.

CT is used to assess many areas of the body, including:

• —brain
• —lungs
• —heart and blood vessels
• —abdomen
• —pelvis
• —bones and joints
• —trauma and injuries.

What does a CT scanner look like?

A CT scanner looks like a large ring or doughnut rather than a long tunnel.

You lie on a flat table that moves through the centre of the scanner.

For most people, CT is less enclosed than MRI and the actual image acquisition is much faster.

How should I prepare?

Preparation depends entirely on the type of CT you are having.

You may be asked to:

• —eat and drink normally
• —avoid eating for a period beforehand
• —drink water before the examination
• —drink oral contrast
• —have blood tests before contrast administration
• —arrive early for preparation
• —change into a gown.

Always follow the instructions provided by the imaging department performing your scan.

Their instructions take priority over general information online.

What should I tell the CT department beforehand?

Tell the team if you:

• —are pregnant or think you may be pregnant
• —have kidney problems
• —have thyroid problems
• —have diabetes
• —have asthma
• —have previously reacted to CT contrast
• —have significant allergies
• —take regular medicines.

These factors do not necessarily mean you cannot have CT or contrast, but the team may need to take them into account when planning your examination.

What happens during the scan?

A radiographer will position you on the CT table.

You may have pillows or supports to help keep you comfortable and correctly positioned.

The radiographer then moves to the control room. They can see and communicate with you throughout the examination.

During the scan:

• —The table moves through the scanner.
• —The X-ray tube rotates around you.
• —You need to remain still.
• —You may be asked to hold your breath for several seconds.

The actual scanning portion can be extremely quick.

The NHS advises that a typical CT appointment often takes around 10–20 minutes, although this varies depending on the examination and preparation required.

Does a CT scan hurt?

The CT scan itself is painless.

You may find holding a particular position uncomfortable if you already have pain or restricted mobility.

Tell the radiographer if you are uncomfortable before the scan begins.

What is CT contrast?

Some CT examinations require iodinated contrast medium.

This is usually injected through a small cannula placed into a vein in your arm.

Contrast makes certain tissues and blood vessels appear more clearly.

It is commonly used for examinations such as:

• —CT chest, abdomen and pelvis
• —CT pulmonary angiography
• —CT coronary angiography
• —CT angiography
• —many cancer-related examinations.

Not every CT scan requires contrast.

What does the contrast injection feel like?

When intravenous contrast is injected, it is common to briefly experience:

• —a warm sensation through the body
• —a metallic taste
• —a sensation as though you have passed urine.

These feelings normally disappear quickly.

Can you be allergic to CT contrast?

Yes, although significant reactions are uncommon.

A recent systematic review of more than 2.5 million contrast-enhanced CT examinations reported acute reactions in a small proportion of examinations and found that a previous contrast reaction was one of the strongest predictors of another reaction.^[4]

This is why you should tell the radiology team if you have previously had a reaction to iodinated contrast.

Most reactions are mild, but serious reactions can occur.

If you feel unwell during or after the injection, tell the radiographer immediately.

Does contrast damage the kidneys?

Modern assessment of kidney risk from iodinated contrast is more nuanced than the older belief that contrast routinely causes kidney injury.

For most people with normal or reasonably preserved renal function, clinically important kidney injury related to intravenous contrast is uncommon.

However, your healthcare team may need to assess kidney function if you have significant kidney disease or other relevant risk factors.

What about radiation?

Unlike MRI and ultrasound, CT uses ionising radiation.

Radiation dose varies considerably depending on:

• —the area being scanned
• —the size of the patient
• —the clinical question
• —the CT protocol
• —the scanner technology.

The radiation exposure from a medically justified CT scan carries a small theoretical long-term risk.

However, the reason your healthcare team has requested the examination is that the expected diagnostic benefit is considered greater than this risk.

CT protocols are designed to use the lowest radiation exposure that provides images of sufficient diagnostic quality.

What if I am pregnant?

Tell the radiology department if you are pregnant or think you may be pregnant.

Whether CT can be performed depends on:

• —the part of the body being examined
• —the urgency of the situation
• —whether an alternative test could answer the same question.

In emergencies, CT may still be the most appropriate investigation.

The clinical team and radiology department will balance the benefits and risks.

What if I am anxious?

Feeling anxious before imaging is common.

Research has shown that people undergoing CT may worry about:

• —the result
• —radiation
• —contrast injections
• —claustrophobia
• —uncertainty about what will happen.^[2]

Clear information can help.

A 2024 study found that both written and audiovisual information reduced anxiety before CT, with audiovisual preparation producing an even greater reduction in that study.^[3]

If you are worried, tell the department beforehand.

Knowing exactly what to expect often makes the experience easier.

What happens after the CT?

Most outpatients can go home shortly after the scan.

If you have received intravenous contrast, some departments may ask you to remain for a short period afterwards.

Unless you have specifically been told otherwise, you can usually return to normal activities.

Follow any instructions given by your own imaging department.

Who looks at my CT scan?

The images are usually interpreted by a radiologist, a doctor specialising in medical imaging.

A CT examination can contain hundreds or thousands of images.

The radiologist reviews them systematically, considers the clinical question and produces a written report.

When will I get my results?

According to current NHS guidance, CT results often take around 1–2 weeks, although they can take longer depending on urgency and local services.^[1]

Urgent or emergency CT scans may be interpreted much sooner.

The radiographer performing the scan will usually not be able to give you the final result at the appointment.

Your referring clinician should tell you how you will receive the result.

Five things to remember

• —Follow the preparation instructions from your own radiology department.
• —Tell the team about pregnancy, kidney problems and previous contrast reactions.
• —CT is generally quick and painless.
• —A warm sensation during contrast injection is common and usually disappears rapidly.
• —CT uses radiation, but examinations are medically justified by weighing expected benefit against risk.