PET-CT scan (Positron emission tomography–computed tomography (PET-CT))
A specialised scan that combines a PET scan with a CT scan, using a small amount of a radioactive tracer to show how tissues are working — often used in cancer to find, stage or check the response of disease.
✓ Medically reviewed by a GMC-registered consultant · last reviewed September 2026 · next review September 2027 · how we review
In short
- A PET-CT combines a tracer-based PET scan with a CT scan to show how tissues are working, often used in cancer to find, stage or monitor disease.
- It is powerful but not perfect: infection or inflammation can also light up, and some cancers show little tracer, so a specialist interprets it with other information.
- It uses a radioactive tracer plus CT, so the radiation dose is higher than an ordinary X-ray — comparable to a few years of natural background radiation.
- Tell staff if you are or might be pregnant or are breastfeeding, and expect to avoid close contact with others, especially children and pregnant people, for the rest of the day.
A plain-English summary. The detail — including risks and recovery — is below.
At a glance
A general guide. Your radiologist will give you advice for your situation.
Can detect active disease, including some cancers, that other scans may miss.
When the clinical question can be answered by a lower-dose or non-radiation test such as ultrasound or MRI.
After the tracer injection you rest quietly for about an hour so it can spread through your body. Moving about can affect the images.
Clear aftercare advice on fluids and limiting contact with children and pregnant people.
After the tracer injection you rest quietly for about an hour so it can spread through your body. Moving about can...
You lie still on a bed moving through the scanner, usually for 30–60 minutes. It is usually not painful but can...
Drink plenty of fluids and empty your bladder regularly to clear the tracer. Avoid prolonged close contact with...
The tracer has largely gone and normal contact is fine. You can return to usual activities.
What is a PET-CT scan?
A PET-CT scan combines two scans in one. The PET (positron emission tomography) part uses a small amount of a radioactive tracer to show how active different tissues are, while the CT (computed tomography) part provides detailed pictures of the body's structure. Together they show both where something is and how it is behaving.
The tracer is usually a form of sugar labelled with a small amount of radioactivity, given by injection into a vein. Cells that are very active — including many cancers — take up more of the tracer and show up brighter on the scan. This makes PET-CT especially useful in cancer, for finding disease, working out how far it has spread (staging), and checking how it responds to treatment.
PET-CT is powerful but not perfect. Some normal tissues and some non-cancer conditions (such as infection or inflammation) can also light up, and some cancers take up little tracer, so results are always interpreted by a specialist alongside other information. A scan cannot, on its own, prove or disprove cancer in every case.
Because it uses both a radioactive tracer and a CT scan, a PET-CT gives a higher radiation dose than a single ordinary X-ray — comparable to a few years of natural background radiation. The dose is justified by the important information the scan provides, and staff keep it as low as possible.
Types, options & approaches
There may be different ways to do this. The right approach depends on the clinical question and your circumstances.
PET-CT versus an ordinary CT scan
| Point | Ordinary CT | PET-CT |
|---|---|---|
| What it shows | Structure / anatomy | Structure plus tissue activity |
| Tracer injection | Not usually | Yes, a radioactive tracer |
| Radiation dose | Moderate | Higher (tracer plus CT) |
| Main use here | Detail of anatomy | Finding and staging active disease |
The right scan depends on the clinical question. PET-CT adds information about how active tissue is, at the cost of a higher radiation dose.
Preparing for your scan
- Follow the fasting instructions you are given — usually no food for about 6 hours before, drinking only water.
- Tell the department if you are, or might be, pregnant, or if you are breastfeeding.
- Tell staff if you have diabetes, as blood sugar affects the scan and you may need special advice.
- Avoid strenuous exercise for a day or so beforehand, as muscle activity can affect the images.
- Wear clothing without metal (zips, poppers), or expect to change into a gown, and remove jewellery.
- Arrange your day so you can avoid prolonged close contact with young children and pregnant people afterwards.
- Bring details of recent scans and a list of your medicines.
What happens
A PET-CT visit usually takes a few hours, although the scan itself is shorter. After checking in and confirming your details, a small cannula is placed in a vein and the radioactive tracer is injected. You then rest quietly for around an hour while the tracer spreads through your body — moving about too much can affect the images.
When you are ready, you lie on a bed that moves slowly through the ring-shaped scanner. You need to lie still, and the scan commonly takes around 30 to 60 minutes. It is usually not painful, though lying still can feel long. Some scans use a CT contrast agent as well, given through the cannula.
Afterwards, you can usually go home. You will be advised to drink plenty of fluids and empty your bladder regularly to clear the tracer, and to avoid prolonged close contact with others — especially young children and pregnant people — for the rest of the day. The images are reviewed by a specialist, who sends a report to your doctor.
Is this scan right for me?
A good consultation should explore whether it's the right choice for you now — including reasons to wait or consider something else.
May not be suitable if…
- When the clinical question can be answered by a lower-dose or non-radiation test such as ultrasound or MRI.
- Routine PET-CT in people with no clear indication, where it would not change management.
- Pregnancy, unless the scan is genuinely essential.
- Poorly controlled diabetes or recent strenuous exercise, until addressed, as these can spoil the images.
Delay or rearrange if…
- You are or might be pregnant, until this is assessed.
- You are breastfeeding and need specific advice first.
- Your blood sugar is too high on the day, for an FDG scan.
- You have an active infection or recent surgery that could confuse the result, where timing matters.
Alternatives to discuss
- Diagnostic CT or MRI for many staging and structural questions.
- Ultrasound, which uses no radiation, for some questions.
- Biopsy, which is often still needed to confirm a diagnosis.
- Other nuclear-medicine scans for specific conditions.
- No scan if it would not change your treatment.
Before you decide
Use this as a shared-decision checklist. The aim is not just “can this be done?”, but whether it is right for you, now, with the risks and alternatives clearly understood.
What matters most to me?
Think about symptoms, daily life, work, caring responsibilities, sport, fertility, travel, appearance and anxiety — the right choice depends on your priorities, not just the medical facts.
What are all my options?
Ask about waiting, monitoring, medicines, rehabilitation, a smaller or larger procedure, a different test, NHS referral, or a second opinion where that would help.
What would make me pause?
Active infection, pregnancy, unstable medical problems, smoking, medicines that increase bleeding, poor support at home, or feeling pressured are all reasons to slow down and get tailored advice.
What happens if I do nothing today?
For some problems, waiting is safe; for others, delay can make treatment harder. A good consultation should explain the trade-off in plain English.
Benefits
- Can detect active disease, including some cancers, that other scans may miss.
- Shows both the location and the activity of tissue in one test.
- Helps stage cancer and plan surgery, radiotherapy or other treatment.
- Can show whether treatment is working, sometimes earlier than other tests.
- May reduce the need for some other investigations by answering several questions at once.
- Whole-body coverage can reveal disease in unexpected places.
Risks & complications
- Discomfort from the cannula and injection.
- Having to lie still for a while, and a long overall visit.
- Needing to fast beforehand and to limit contact with others afterwards.
- Incidental findings — areas that light up but turn out not to be cancer, sometimes needing more tests.
- False positives (infection or inflammation showing up) and false negatives (some cancers showing little tracer).
- Bruising at the injection site.
- Allergic reaction to a CT contrast agent, where one is used.
- A very small increase in lifetime cancer risk from the combined radiation dose.
- Risk to a pregnancy or to a breastfed baby, which is why pregnancy and breastfeeding are checked first.
A PET-CT uses both a radioactive tracer and a CT scan, so the radiation dose is higher than an ordinary X-ray — typically comparable to a few years of natural background radiation. This is justified by the important information it gives, usually in cancer. The biggest day-to-day issues are incidental findings and false results, so the scan is always interpreted by a specialist alongside your other tests. Tell staff if you are or might be pregnant or are breastfeeding.
Published figures to discuss
PET-CT accuracy varies with the type of cancer, the tracer and the clinical situation, so single accuracy figures are not meaningful and are not given here. The key points to understand are that some normal or inflamed tissue can take up tracer (false positives) and some cancers take up little tracer (false negatives), and that the combined tracer-and-CT radiation dose is higher than an ordinary X-ray, typically comparable to a few years of natural background radiation.
| Figure | Reported range | How to interpret it | Source / confidence |
|---|---|---|---|
| Radiation dose, whole-body FDG PET-CT | Comparable to roughly 3–4 years of natural UK background radiation (an order of magnitude or more above a chest X-ray) | Exact dose depends on the tracer activity and the CT settings used; staff keep it as low as reasonably possible. | Guide sourcesClinical context |
| False-positive FDG uptake | Common because infection and inflammation can be metabolically active | PET-CT findings often need correlation with CT appearance, history, biopsy or follow-up. | Royal College of Radiologists — Benefits and risks of imaging (patient information)rcr.ac.ukSource-linked context |
| Small or low-grade tumour being missed | Possible | Some cancers are not strongly FDG-avid, and very small lesions may be below resolution. | Guide sourcesClinical context |
These are literature figures, not a personalised prediction. Your own risks and likely benefits depend on your circumstances, your health, and how your care is carried out and followed up.
What happens afterwards
There is no physical recovery from the scan itself, but you carry a small amount of radioactivity for a few hours, so you will be asked to limit close contact with others, especially young children and pregnant people, for the rest of the day.
- Feeling normal physically after the scan.
- Passing more urine as you flush out the tracer.
- Mild bruising or tenderness where the cannula was.
- Waiting a few days for the specialist report.
Aftercare
- Drink plenty of fluids and empty your bladder regularly to clear the tracer.
- Avoid prolonged close contact with young children and pregnant people for the rest of the day.
- If you are breastfeeding, follow the specific advice you are given about feeding and contact.
- Resume eating and your usual medicines as advised.
- Make sure you know who will give you the results and when.
- Keep your follow-up appointment to discuss the findings and any next steps.
- Fasting and diabetes instructions followed.
- Pregnancy or breastfeeding declared to staff.
- A plan to avoid close contact with children and pregnant people afterwards.
- Plenty of fluids planned for the rest of the day.
- Details of recent scans and your medicines brought along.
- Knowing how and when you will receive results.
⚠ Get urgent help if…
- Signs of an allergic reaction after a contrast agent — rash, swelling, wheeze or breathing difficulty (call 999 if severe).
- Severe pain, swelling or spreading redness at the injection site.
- New severe symptoms while waiting for results — seek medical advice.
- Any collapse, severe breathlessness or chest pain — call 999.
- Realising you may be pregnant or are breastfeeding when you were not asked — tell the department.
- Not receiving your results in the expected time — chase them up.
Who to contact: your clinician, clinic or test provider first (keep their number to hand). For urgent advice when you can't reach them, call NHS 111. In an emergency, call 999.
General guidance — it doesn't replace the specific advice your radiologist gives you.
Results & realistic expectations
A PET-CT report describes where tracer uptake is increased and what it is likely to mean, combined with the CT detail. In cancer, this helps confirm a diagnosis already suspected, show how far disease has spread, or whether treatment is working. A specialist interprets it alongside your other tests and scans.
A PET-CT cannot, by itself, prove or rule out cancer in every case. Infection and inflammation can light up (false positives), and some cancers take up little tracer (false negatives), so a biopsy or further tests are sometimes needed to be sure. Your doctor will explain what the result means for you.
A PET-CT is a snapshot of disease activity at one point in time. In cancer care, scans are often repeated to check response to treatment or to look for recurrence, so a single scan does not give a permanent answer. Because each scan carries a radiation dose, repeats are planned only when they will change management.
Related tests, treatments or support
PET-CT is usually one part of a wider assessment. It is often combined with other scans (such as MRI or diagnostic CT), blood tests and a biopsy, and the results are discussed by a multidisciplinary team. The CT part of the PET-CT may itself be done with or without contrast depending on the question.
Follow-up & long-term care
A specialist reports the scan and sends the findings to your doctor or cancer team, usually within several days. Results are often discussed at a multidisciplinary team meeting before being explained to you. Ask who will give you the results, when, and what the next step is depending on what the scan shows.
Repeat, follow-on and what comes next
- Findings may be unclear and need a biopsy or further scans to confirm.
- Scans are often repeated to check treatment response or recurrence.
- False positives can lead to additional, sometimes invasive, tests.
- A negative scan does not always rule out disease and may need follow-up.
Ask what happens if the result is unclear or needs repeating, and what is included if further tests or follow-up are needed.
What good aftercare looks like
- Clear aftercare advice on fluids and limiting contact with children and pregnant people.
- A defined route to the specialist report and who will explain it.
- Discussion of results in a multidisciplinary team where appropriate.
- A clear plan for biopsy or further tests if the scan is unclear.
- Sensible use of repeat scans, balancing benefit against dose.
What affects the cost
Costs vary a great deal between people and providers, and we don't publish prices. What matters is understanding what drives the cost and making sure your quote is complete. The main things that affect it:
- The type of scan and tracer used (some specialist tracers cost more).
- Whether a CT contrast agent is included.
- The reporting specialist's fee and how quickly results are provided.
- The facility fee and the cost of producing the tracer.
- Whether a follow-up consultation to explain results is included.
- Whether further tests, such as a biopsy, are then recommended.
- The scan and tracer fee and the reporting specialist's fee.
- Whether contrast is included and any extra cost.
- How and when you will receive the written report.
- Whether a consultation to discuss results is included.
- What happens, and any cost, if further tests are recommended.
- The cancellation policy and what happens if the scan is inconclusive.
On the NHS? PET-CT is available on the NHS when clinically indicated, usually in cancer care; private scans may be used for speed or choice, but should still only be done when they will change your management.
You're entitled to your total cost in writing — including reports, follow-up and what happens if the result is inconclusive — before you decide.
Consent traps and marketing red flags
These are not small details. They are often where patients lose choice, time to reflect, or realistic expectations.
Consent traps
- Not being told the scan can give false positives or false negatives.
- Pregnancy or breastfeeding not being checked before the scan.
- No clear explanation of the higher radiation dose.
- No plan for who explains the result and what happens if it is unclear.
- Incidental findings not being explained or followed up.
Marketing red flags
- Offering whole-body PET-CT as a 'cancer screen' for healthy people with no symptoms.
- Implying a normal PET-CT rules out all cancer.
- Downplaying the radiation dose or aftercare precautions.
- Promising instant or guaranteed answers without specialist reporting and, where needed, biopsy.
- Encouraging frequent repeat scans without clear clinical need.
Choosing a specialist safely
- Check the radiologist is on the GMC Specialist Register for this area.
- Make sure they work at a CQC-registered service, and look for membership of the relevant Royal College or professional body.
- You're entitled to time to consider and to have your questions answered before you agree — the radiologist who looks after you should explain it, not a salesperson.
- Be wary of pressure: time-limited offers or deposits taken before you've had time to think are red flags, not bargains.
- You're entitled to your total cost in writing — including any follow-up — before you decide.
Questions to ask your medical professional
Take this to your consultation. A good radiologist will welcome every one of these.
- Why is a PET-CT the right scan for me, and what will the result change?
- What happens if it shows something unexpected or unclear?
- Could the result be a false positive or false negative, and would I need a biopsy?
- How does the radiation dose compare with other scans I might have?
- What precautions do I need afterwards, especially around children or if breastfeeding?
- Who will explain my results, and when?
- Are you on the GMC Specialist Register for this area, and which Royal College or professional body are you a member of?
- Will you be the radiologist who carries out my scan, and who looks after me afterwards?
- What are the risks for someone like me, and how often do your own patients have a problem or need it repeated or redone?
- What does a realistic result look like — and what can this scan not achieve?
- What are my options, including waiting, doing nothing for now, or choosing a different approach?
- Can I have written information, results and aftercare instructions in a format I can use, including any accessibility or communication support I need?
- What is the total cost in writing, including any follow-ups, and how much time do I have to decide?
Frequently asked questions
Is a PET-CT available on the NHS?
How much radiation does a PET-CT involve?
Is the radioactive tracer dangerous to others?
Does a PET-CT prove whether I have cancer?
Can I have a PET-CT if I am pregnant or breastfeeding?
Why do I have to fast and avoid exercise beforehand?
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How we made this page
Medically reviewed by a GMC-registered consultant. Written in plain English, checked against NHS, NICE, GMC and relevant Royal College / specialist-society guidance, and kept under review. No clinic paid to appear on this page, and we publish no pricing. This is general information to help you prepare — it is not a substitute for advice from your own clinician. How we review our guides →
Source hierarchy: UK regulator and NHS/NICE guidance first, then relevant Royal College or specialist-society guidance, then peer-reviewed evidence for procedure-specific figures where available.
Sources & standards: NHS — PET scan UKHSA / GOV.UK — Ionising radiation: dose comparisons Royal College of Radiologists — Benefits and risks of imaging (patient information) Cancer Research UK — PET-CT scan IAEA — Radiation protection of patients during PET/CT
Reviews reflect patients' experience of care, not clinical outcomes. For procedure volumes and outcome data see PHIN.
Last medically reviewed 2026-09-21. Spotted something wrong or out of date? Report an error in this guide.
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