What PET-CT looks for
Informed by recognized medical guidance
Overview
A PET-CT scan is a type of imaging test that combines two methods — PET (Positron Emission Tomography) and CT (Computed Tomography). It helps doctors find areas of abnormal activity in the body, such as cancer, infection, or inflammation. The scan uses a small amount of a radioactive substance (called a tracer) that shows up on images where cells are more active than usual.
Key facts
- PET-CT can detect many cancers and see if treatment is working.
- It can also find areas of inflammation or infection.
- The scan is painless and usually takes about 30 to 60 minutes.
PET-CT scans are a common and widely used imaging tool in hospitals around the world, especially for diagnosing and monitoring cancer.
People of any age may have a PET-CT scan, but it is most often used in adults when there is a concern about cancer, or to check how well cancer treatment is working. It may also be used for certain infections or heart conditions.
Symptoms
- If you have a severe allergic reaction after the tracer injection — such as trouble breathing, swelling of the face or throat, or hives — call your local emergency number immediately.
- If you experience chest pain, severe shortness of breath, or feel like you are going to pass out during or after the scan.
- ⚠If you develop a high fever or chills within a few hours after the scan.
- ⚠If you have pain or redness at the injection site that gets worse.
Common symptoms
- Unexplained weight loss
- Persistent fever or night sweats
- Lumps or swellings that do not go away
- Unexplained pain
Symptoms in children
- In children, a PET-CT may be used to look for certain cancers (like lymphoma) or to check treatment response. Symptoms that might lead to a scan include unexplained fevers, weight loss, or swollen lymph nodes.
Symptoms in older adults
- In older adults, symptoms like unexplained weight loss, persistent cough, or changes in bowel habits might lead to a PET-CT scan. It can also help tell the difference between benign (non-cancerous) and malignant (cancerous) growths.
Causes
Main causes
- A PET-CT scan is not caused by a disease — it is a test used to investigate possible conditions. Doctors may order it when symptoms suggest cancer, infection, or inflammation.
Risk factors
- Having certain symptoms (like unexplained weight loss, persistent fever, or a lump) may lead your doctor to recommend a PET-CT scan.
- Having a history of cancer may mean you need periodic PET-CT scans to monitor for return of disease.
- Being at risk for certain conditions, such as chronic infections, may also prompt a scan.
When to see a doctor
See a doctor urgently if:
- If you have any new or worsening symptoms that worry you — like unexplained weight loss, persistent fever, or a lump that is growing — see a doctor promptly.
Book a routine appointment if:
- Talk to your doctor about a PET-CT scan if you have been diagnosed with cancer and are due for a follow-up scan.
- If you have a condition like sarcoidosis or a chronic infection, your doctor may schedule a PET-CT to check how things are going.
Diagnosis
A PET-CT scan is a diagnostic imaging test, not a disease. It helps diagnose conditions by showing areas of increased cellular activity. The results are interpreted by a radiologist (a doctor trained in reading scans).
Tests that may be done
- Before the scan, you may have a blood test to check your kidney function (the tracer is removed through the kidneys).
- You will receive an injection of a radioactive tracer (usually a small amount of radioactive glucose).
- The scan itself takes about 30–60 minutes, during which you lie still on a table that moves through the scanner.
What to expect at your appointment
You will be asked to fast (not eat or drink anything except water) for a few hours before the scan. After the injection, you will wait about an hour for the tracer to spread through your body. During the scan, you will be asked to lie still and breathe normally. The entire visit usually takes 2–3 hours. Afterward, you can resume normal activities. The tracer leaves your body naturally in a few hours.
Treatment
A PET-CT scan itself is not a treatment. The information from the scan helps guide treatment. If cancer is found, treatment may include surgery, radiation therapy, chemotherapy, targeted therapy, or immunotherapy. For infections or inflammation, antibiotics or anti-inflammatory medications may be used.
Self-care at home
- Stay well hydrated before and after the scan to help remove the tracer.
- Follow your doctor's instructions about eating and drinking before the scan.
- If you have needle anxiety, tell the staff — they can help you feel more comfortable.
Medical treatments
Treatments depend on what the scan finds. For cancer, common approaches include surgery, radiation, chemotherapy (medicines that kill cancer cells), targeted therapy (drugs that attack specific cancer cell features), or immunotherapy (helps your immune system fight cancer). For infections, antibiotics or antiviral drugs are used. Your doctor will discuss the best plan for you.
When is surgery considered?
If a PET-CT shows a localized tumor (one that has not spread), surgery may be an option to remove the cancer. The scan can also help surgeons plan the operation.
Living with this condition
If a PET-CT finds a condition, your daily life may change depending on the diagnosis and treatment. For many people with cancer, treatment can be tiring, but most continue their normal activities as much as possible. For infections or inflammation, rest and medication are often needed.
Lifestyle tips
- Get plenty of rest, especially if you are undergoing treatment.
- Stay physically active as much as you feel able — even short walks can help.
- Eat a balanced diet to support your strength and immune system.
Diet and exercise
A healthy diet with lots of fruits, vegetables, whole grains, and lean protein can help you feel better. Gentle exercise, like walking or stretching, can reduce fatigue and improve mood. Always check with your doctor before starting a new exercise program.
Mental health and emotional wellbeing
Waiting for results or dealing with a new diagnosis can cause anxiety, sadness, or stress. It is normal to feel this way. Talk to your doctor or a mental health professional. You are not alone.
Prevention
A PET-CT scan is not something to prevent — it is a tool to detect disease. You can reduce your risk of conditions that might require a PET-CT by maintaining a healthy lifestyle: avoid smoking, limit alcohol, eat well, exercise, and get recommended cancer screenings.
Vaccines
Vaccines like the HPV vaccine (for human papillomavirus) and the hepatitis B vaccine can prevent some cancers. The flu and pneumonia vaccines can help prevent infections that might cause inflammation.
Screening programmes
Routine cancer screenings (like mammograms, colonoscopies, and Pap tests) can find cancer early, sometimes before symptoms arise. Talk to your doctor about which screenings are right for you.
Complications
If left untreated
- If a condition found by PET-CT is not treated, it may progress. For example, an untreated cancer can grow and spread, making it harder to treat.
- Untreated infections can become severe or spread to other parts of the body.
- Untreated inflammation can cause long-term damage to organs.
Long-term outlook
Thanks to tools like PET-CT, doctors can find problems earlier and more accurately. Many conditions caught early can be treated successfully. Even if a diagnosis is serious, treatments continue to improve, and support is available to help you through it.
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Always verify with your doctor
Health guidelines vary by country and region. The information in this article is based on international clinical guidelines but may not reflect the specific guidelines, medications, or practices in your country. Always discuss your health concerns with your own doctor or healthcare provider, and refer to your local national health guidelines where available.
Important notice This information is for educational purposes only. It does not replace professional medical advice, diagnosis, or treatment. Always consult a qualified healthcare provider about your specific situation. If you are experiencing a medical emergency, call your local emergency services immediately.
Related conditions
Sources and guidance
This article is educational and is prepared with reference to recognized health information and clinical guidance sources where available. Specific source links may vary by topic.
Last updated: July 19, 2026
Educational note: This information is for education only and is not a diagnosis.
Use it to support, not replace, advice from a licensed clinician.
If symptoms are severe, worsening, or urgent, call your local emergency number or seek emergency care.