CT Scan

A CT scan (Computed Tomography scan) is a diagnostic imaging test that uses a rotating X-ray machine and a computer to build detailed, cross-sectional pictures of the inside of your body.

As you lie still on a narrow table, the scanner rotates around you and takes many X-ray images from different angles. A computer then combines all those images into 'slices' — like the pages of a book — giving doctors a clear view of organs, bones, blood vessels, and soft tissues that a standard X-ray cannot show.

Doctors order a CT scan when they need a more detailed picture than a standard X-ray can provide. It is used both to detect a problem in the first place and to monitor how a known condition is responding to treatment.

• Head and brain: detecting stroke (a blockage or bleed in the brain), head injuries, tumours, or bleeding inside the skull
• Chest: examining the lungs, heart, and major blood vessels for conditions such as pneumonia, pulmonary embolism (a blood clot in the lung), or aortic aneurysm (a bulge in the main artery)
• Abdomen and pelvis: investigating pain, checking the liver, kidneys, pancreas, spleen, and bowel for tumours, cysts, or stones
• Bones and joints: finding fractures (breaks), infections, or tumours in the skeleton
• Blood vessels: mapping arteries before surgery or detecting narrowings and blockages
• Cancer staging: finding out how far a cancer has spread through the body
• Guiding procedures: helping doctors place a needle accurately when taking a tissue sample (biopsy)

A CT scan may not be the best choice in certain situations. Your doctor will weigh the benefits against the considerations below.

• Pregnancy: radiation exposure to the unborn baby is a concern; an ultrasound or MRI is usually preferred
• Severe kidney problems: the contrast dye (a liquid injected to highlight blood vessels and organs) used in some CT scans is processed by the kidneys and may cause further strain
• Known allergy to contrast dye: special precautions or an alternative scan may be needed
• Children: because they are more sensitive to radiation, doctors carefully consider whether the benefit outweighs the exposure

A CT scan is generally a very safe procedure; for most adults, the information it provides far outweighs the small risks involved.

• Radiation exposure: a CT scan delivers more radiation than a plain X-ray, but the dose for a single scan is considered low for most adults; your doctor requests it only when the benefit justifies it
• Contrast dye reaction (mild): some people feel warm, flushed, or briefly nauseous after the dye is injected — this usually passes within minutes
• Contrast dye reaction (allergic): in rare cases, the dye causes hives (an itchy skin rash), swelling, or breathing difficulty; hospital staff are trained and equipped to manage this immediately
• Contrast-induced kidney strain: the dye can temporarily affect kidney function, particularly in people who already have kidney disease; doctors check kidney blood tests before using dye in at-risk patients
• Anxiety or discomfort: some people feel anxious inside the scanner, though the machine is open at both ends and scans are usually quick

What you need to do before a CT scan depends on which part of the body is being scanned and whether contrast dye will be used. Your care team will give you specific instructions; the points below cover what is typical.

Fasting and diet: if contrast dye will be injected or swallowed, you will usually be asked not to eat or drink (except plain water) for a few hours beforehand. If no dye is used, fasting is often not required.

Medications: most regular medications can be continued, but your doctor may ask you to pause blood thinners or diabetes tablets for a short period if contrast dye is involved. Always bring a list of everything you take.

Clothing and metal: wear loose, comfortable clothing. You will be asked to remove metal objects — jewellery, belts, glasses, hearing aids — because they can interfere with the images.

Pre-scan tests: if contrast dye is planned, the team usually checks your kidney function with a blood test beforehand. People with a history of dye allergy may be given antihistamines (anti-allergy medicine) or steroids (anti-inflammatory medicine) before the scan.

During the procedure, the steps are generally as follows, though the order and details can vary:

• You change into a hospital gown if needed and remove all metal objects
• If contrast dye is being used, a small cannula (a thin plastic tube) is placed into a vein in your arm
• You lie flat on a motorised table; a foam pad or pillow may be placed under your knees for comfort
• The table slides you slowly into the centre of the ring-shaped CT machine
• You will hear humming and clicking sounds as the machine rotates — this is normal
• A staff member may ask you to hold your breath for a few seconds during certain images to reduce blur
• If contrast dye is used, it is injected through the cannula at the right moment; you may feel a brief warm sensation
• The table slides back out; the cannula is removed if no longer needed
• The entire scan usually takes between a few minutes and half an hour, depending on the area examined

Recovery from a CT scan is almost immediate for most people — it is a non-invasive (no cuts or entry into the body) test, so there is no wound to heal and no anaesthetic (sleep medicine) to recover from. The main aftercare steps relate to flushing out any contrast dye and waiting for your results.

• Leaving the department: most people can dress and leave the radiology department as soon as the scan is finished; you can usually drive yourself home unless you were given a sedative (calming medicine) beforehand
• Hydration after contrast dye: if dye was used, drinking plenty of water in the hours that follow helps the kidneys clear it from your body — your team will advise how much is appropriate for you
• Cannula site: if a cannula was placed in your arm, a small plaster covers the spot; mild bruising may appear but usually fades within a few days
• Watching for delayed reactions: in the rare event of a delayed allergic reaction to contrast dye — such as a new rash, swelling, or difficulty breathing appearing hours later — seek medical attention promptly
• Kidney monitoring: patients known to have reduced kidney function may be asked to have a follow-up blood test a day or two later to confirm their kidneys have handled the dye without difficulty
• Returning to normal activities: there are no standard restrictions on eating, drinking, or physical activity after an uncomplicated CT scan
• Getting your results: a radiologist (a doctor who specialises in reading medical images) analyses the scans and sends a report to your referring doctor, who will then discuss the findings with you; turnaround times vary by hospital and urgency