PET-CT Scan

A PET-CT scan combines a small radiotracer dose with detailed images to show body structure and activity.

The radiotracer is usually FDG, a substance related to glucose. Areas that use more of it may appear more active on the PET images. The CT part shows the location and shape of tissues, helping the specialist interpret the PET findings. Learn more about the [FDG Radiotracer](/materials/fdg-radiotracer/) and [PET-CT Scanner](/technology/pet-ct-scanner/).

You receive the radiotracer through an injection and then rest quietly while it travels through your body. You will lie on a narrow table that moves through the scanner. The scan itself does not involve cutting or a biopsy; staying still helps produce clear images.

Tell the imaging team about diabetes, pregnancy, breastfeeding, medicines, difficulty lying flat, or trouble with enclosed spaces. You may be asked to avoid food for a period before the appointment while drinking plain water, according to the centre's instructions.

PET-CT uses ionising radiation, so the imaging team considers whether the information is likely to help before recommending it. The radiotracer leaves the body over time, mainly through urine. The injection can cause brief discomfort, and allergic reactions are uncommon but should be reported promptly.

A PET-CT can show patterns that support cancer assessment, but it cannot identify every abnormality or prove cancer on its own. Inflammation, infection, recent treatment, and normal tissue activity can affect the appearance. Your clinician may combine the images with examination findings, blood tests, or a biopsy.

An area of increased activity does not automatically mean cancer. A radiologist reviews the images and sends a report to the clinician who requested the scan. The next step may be comparison with earlier images, another scan, clinical follow-up, or tissue sampling.

The meaning depends on the body area, your symptoms, previous treatment, and the CT appearance. If the scan is being used to investigate cancer found in an unusual location, your care team may discuss [Cancer of Unknown Primary](/conditions/cancer-of-unknown-primary/) or [Lymphoma](/conditions/lymphoma/) when relevant.

The PET image shows activity; the CT image provides anatomical detail. The two sets of information are interpreted together.

A clinician may request this scan to help stage a known cancer, investigate suspected spread, assess a response to treatment, or look for a source of cancer-related findings. It is selected when information about tissue activity could change the care plan.

Not every tumour or symptom requires PET-CT. The decision depends on the suspected condition, prior imaging, treatment history, and whether another test would answer the clinical question more clearly.

Follow the appointment instructions about eating, drinking, exercise, and medicines. Wear comfortable clothing and remove metal objects if requested. After the tracer is injected, rest without strenuous movement so muscles do not take up extra tracer. During imaging, breathe normally and tell staff if you need help staying comfortable.

Most people return to usual activities after the appointment unless their care team advises otherwise. Drinking water and urinating regularly can help clear the tracer. Keep any instructions about close contact, breastfeeding, or medicines specific to your appointment, since these depend on the tracer and your circumstances.

Possible issues include injection-site soreness, a reaction to the tracer, radiation exposure, and anxiety in the scanner. Kidney problems, diabetes, pregnancy, and breastfeeding may alter preparation or the choice of test. Contact the imaging service urgently if you develop marked swelling, breathing difficulty, or other severe symptoms after the injection.

Depending on the question, alternatives may include CT alone, MRI, ultrasound, a bone scan, or a biopsy. These tests provide different kinds of information; one may be more suitable because of pregnancy, metal implants, kidney function, or the body area being assessed.

Choose an imaging service that can review your medical history, give clear preparation instructions, and arrange specialist reporting. Bring previous scans and the details of your medicines. Ask who will explain the report and how follow-up will be arranged.