Understanding CT Scans
3:15 - Video coming soonComputed Tomography (CT) scan, formerly known as a computerized axial tomography (CAT) scan, is a medical imaging technique that uses X-rays combined with advanced computer processing to produce cross-sectional (sliced) images of the body. CT scans can quickly and accurately show bones, soft tissues, blood vessels, and organs, making them invaluable for diagnosing injuries, detecting diseases, and guiding treatment.
How does a CT scan work?
A CT scanner uses a rotating X-ray beam and detectors to take multiple images from different angles. A computer then combines these images to create detailed cross-sectional pictures of the body.
What conditions can a CT scan detect?
CT scans are versatile and can evaluate nearly every part of the body. They are commonly used to detect:
- Head injuries, stroke, or bleeding in the brain
- Chest problems (like pneumonia, lung nodules, or blood clots)
- Abdominal pain (appendicitis, kidney stones, liver or pancreatic issues)
- Bone fractures or spine problems
- Tumors, cancers, and infections
- Internal injuries after trauma
Why choose CT over other scans?
CT scans are very fast and give detailed images of both bone and soft tissue. They are excellent in emergencies, when quick diagnosis is crucial. While MRI is better for some soft-tissue problems, CT is faster, more widely available, and ideal for detecting bleeding, fractures, or lung disease.
How is CT different from MRI?
- CT: Uses X-rays (radiation), takes only a few minutes, ideal for emergencies and bone/lung problems.
- MRI: Uses strong magnets and radio waves, takes longer, better for soft-tissue detail (brain, muscles, joints).
Both can complement each other depending on what your doctor is looking for.
Who can benefit from a CT scan?
CT is useful when the expected information is likely to change diagnosis or treatment, especially in emergencies, trauma, and selected chest, abdominal, bone, or blood-vessel problems. The referring clinician and imaging team should match the scan and body area to a specific clinical question and consider ultrasound or MRI when either would answer it adequately without ionising radiation.
Is a CT scan safe?
CT uses ionising radiation. A medically justified scan usually offers substantially more benefit than its small potential radiation risk, but the dose varies with the body area, protocol, patient size, and number of phases. Children require size-adjusted protocols, and unnecessary repeat or multiphase imaging should be avoided.
Pregnancy Precaution
If you are pregnant or could be pregnant, tell the referring clinician and CT team before imaging. Ultrasound or MRI may be preferred when they can answer the question in time, but a necessary CT should not be withheld when delay could harm you.
What about contrast dye?
Many CT scans use a special dye (contrast) to make blood vessels and organs show up more clearly. The dye may be swallowed, injected into a vein, or both.
Safety Note
Most people tolerate modern iodinated contrast well. Allergic-like reactions can occur and severe reactions are rare. Kidney-function testing is based on risk factors and local policy rather than being required for every patient. The risk that intravenous contrast itself causes acute kidney injury has historically been overstated, although people with acute kidney injury or severe chronic kidney disease need individual review.
Be sure to inform your radiographer if you have:
- Previous reactions to contrast
- Kidney disease
- Asthma or severe allergies
- Diabetes, thyroid disease, recent acute illness, or possible pregnancy
- Metformin or other medicines the centre asks you to report
How should I prepare before my CT scan?
Usually, you can eat and drink normally before a CT scan unless you are specifically instructed otherwise (for example, for some abdominal scans or if contrast will be used). Practices may vary between facilities, so don’t be surprised if fasting is recommended though drinking water is generally fine.
Wear comfortable clothing; you might be asked to change into a hospital gown.
Do I need to stop taking medication?
Do not stop prescribed medication unless your clinical team tells you to. Metformin is not routinely withheld for every contrast CT; the decision depends on kidney function, acute kidney injury, and the type of contrast procedure. Follow the centre's specific instructions.
What happens when I arrive for my CT scan?
You will check in and may fill out a brief questionnaire about your medical history, allergies, and prior reactions to contrast. The radiographer will explain the procedure and may ask you to sign a consent form if contrast is required.
What happens during the scan?
You will lie on a table that slides through a short, doughnut-shaped machine. The scanner will move around you, taking pictures. Try to lie as still as possible to ensure clear images.
Will the scan be painful?
The imaging itself does not usually hurt, but an IV, existing injuries, lying still, oral contrast, or bowel inflation can cause discomfort. IV contrast may cause a brief warm sensation, metallic taste, or feeling of urination. Tell staff immediately about pain or swelling at the injection site, hives, breathing difficulty, or feeling faint.
How long does the scan take?
Most CT scans take 5–15 minutes. With contrast, it may take a little longer. The actual scanning time is very short.
Can I talk to someone during the scan?
Yes, you will be in communication with the radiographer through an intercom. If you feel uncomfortable, you can alert them at any time.
Are there restrictions after the scan?
Most people can resume normal activities immediately. Follow separate instructions if you received sedation, heart-rate medicine, bowel medication, or another treatment. Resume your usual fluids unless your team has restricted them; forcing extra water is not necessary for most people.
Can I breastfeed after iodinated CT contrast?
Yes. Only a very small amount reaches breast milk and an even smaller amount is absorbed by the infant, so routine interruption of breastfeeding is not required after iodinated contrast. If you have an unusual clinical circumstance or remain concerned, discuss it with the radiologist rather than discarding milk automatically.
When will I get my results?
A radiologist will review the images and send a report to the referring clinician. Timing varies by urgency and facility, so ask when and how you will receive the result. Emergency findings may be communicated directly to the treating team.
Can children have CT scans?
CT can be performed in children when it is clinically justified. The protocol should be adjusted to the child's size and the diagnostic task, and alternatives that use no radiation should be considered when they are equally suitable.
What if I am pregnant or think I might be pregnant?
Pregnancy Precaution
Tell the referring clinician and CT team before the scan. Ultrasound or MRI may be used when they can provide the required answer without harmful delay. If CT is the most appropriate test for a serious or urgent condition, pregnancy is not an automatic reason to refuse or postpone it; the team should optimise the protocol and discuss benefits and risks.
Can a CT scan detect cancer?
CT can detect masses and other changes that may represent cancer, show disease extent, guide biopsy, and monitor treatment. It cannot identify every cancer or always distinguish cancer from benign disease; additional imaging, endoscopy, laboratory testing, or biopsy may be required.
Questions to ask your team
- What clinical question will CT answer, and could ultrasound or MRI answer it without radiation?
- Will I receive oral or IV contrast, and what preparation applies?
- Are pregnancy, kidney problems, diabetes medicines, thyroid disease, or a previous contrast reaction relevant?
Sources and further reading
- FDA: Computed tomography benefits and risks
- RadiologyInfo: Body CT
- RadiologyInfo: CT safety during pregnancy
- ACR Manual on Contrast Media
Conclusion
CT is a fast and valuable diagnostic tool when the examination is justified and tailored to the clinical question. Share pregnancy, previous imaging, kidney disease, medicines, and prior contrast reactions, and follow the preparation instructions issued for your exact protocol.