Preparing for PET-CT

Overview

A PET-CT scan is a medical imaging test that combines two types of scans: a PET scan (which shows how your cells are working) and a CT scan (which gives detailed pictures of the inside of your body). Together, they help doctors find areas of disease or injury. Preparing properly helps make sure the scan is safe and gives clear results.

PET-CT scans are common tests used to diagnose, monitor, or stage many conditions, especially cancers, infections, and inflammatory diseases.

People of all ages, including children and older adults, may have a PET-CT scan if their doctor needs detailed information about a health condition.

Symptoms

Common symptoms

• Unexplained weight loss
• Persistent fever or night sweats
• Lumps or swelling in the body
• Pain that does not go away
• Fatigue without a clear cause

Symptoms in children

• Frequent infections that do not get better
• Slow growth or weight loss
• Persistent pain or swelling

Symptoms in older adults

• Changes in energy or appetite
• New or worsening pain
• Unexpected weight loss
• Persistent fever or weakness

Causes

Main causes

• Cancer – to find tumors or see if they have spread
• Infection – to locate hidden infections
• Inflammation – to check for diseases like sarcoidosis or vasculitis
• Heart or brain conditions – to evaluate blood flow or activity

Risk factors

• A family history of certain cancers
• A known diagnosis of cancer or chronic infection
• Having symptoms that suggest inflammation or hidden disease

When to see a doctor

See a doctor urgently if:

• If you experience a severe allergic reaction after the tracer injection (e.g., trouble breathing, swelling)
• If you develop a high fever or severe pain on the day of the scan

Book a routine appointment if:

• If you have questions about how to prepare for the scan (e.g., whether to stop taking certain medicines)
• If you think you might be pregnant or are breastfeeding – tell your doctor or the scanning team beforehand
• If you have diabetes and use insulin – you may need special instructions

Diagnosis

Your doctor will decide if a PET-CT scan is needed based on your symptoms, medical history, and other test results. The scan itself is not a diagnosis – it gives images that your radiologist will interpret and share with your doctor.

Tests that may be done

• You may have blood tests before the scan, such as a pregnancy test if you could be pregnant.
• You might need a blood sugar test because the tracer is affected by high blood sugar.
• You may also have other scans, like an MRI or CT, to compare with the PET-CT results.

What to expect at your appointment

On the day of the scan, you will arrive at the hospital or imaging centre. You will be asked to change into a gown and remove metal objects. A nurse or technologist will insert a small needle into a vein in your arm to give you the radioactive tracer. You will then wait in a quiet, dimly lit room for about 45 to 60 minutes while the tracer spreads through your body. During the scan, you lie on a padded table that slides into the machine. It is important to stay very still. The machine makes humming or clicking sounds. After the scan, you can go back to your normal activities, but you should drink extra water to help flush the tracer out of your body.

Treatment

A PET-CT scan is not a treatment – it is a test that helps guide your treatment. The results can show whether a disease is active, how far it has spread, and how well your current treatment is working. Based on the scan, your doctor may recommend treatments such as medicines, radiation therapy, or surgery.

Self-care at home

• Follow all preparation instructions given by your healthcare team, especially about when to stop eating and drinking.
• Tell your doctor about all medicines and supplements you take – some may need to be stopped before the scan.
• Wear loose, comfortable clothing without metal fasteners on the day of the scan.
• After the scan, drink plenty of water to help your body remove the tracer.

Medical treatments

Treatment depends on the condition being investigated. For example, if the scan shows cancer, your doctor may discuss options such as chemotherapy, radiation therapy, targeted therapy, or immunotherapy. For infections, antibiotics may be prescribed. Your healthcare provider will explain what the results mean for you and suggest the best next steps.

When is surgery considered?

If the scan shows a tumor that can be removed, surgery may be an option. The decision to have surgery depends on the size, location, and type of the abnormality, as well as your overall health.

Living with this condition

After your PET-CT scan, you can usually return to your normal routine immediately. The tracer leaves your body naturally within a few hours. You may need to wait a few days to a week for your results. This waiting period can be stressful – try to keep busy and talk to your loved ones.

Lifestyle tips

• Stay well hydrated – drink extra water on the day of and after your scan.
• Avoid close contact with pregnant women, babies, and young children for a few hours after the scan, as the tracer is very slightly radioactive. Your team will tell you exactly how long.
• Continue any treatments or medicines as directed by your doctor.

Diet and exercise

There are no diet or exercise restrictions after the scan, unless your doctor advises otherwise. Drink fluids to help flush the tracer. If you feel well, you can go back to your usual exercise routine.

Mental health and emotional wellbeing

Waiting for scan results can cause anxiety or worry. It is normal to feel nervous. Talk to your healthcare team about when you can expect results. If you feel overwhelmed, reach out to a trusted friend, family member, or a mental health professional.

Prevention

The need for a PET-CT scan depends on having a condition that requires investigation. You cannot always prevent the conditions that lead to a PET-CT, such as cancer or infection. However, living a healthy lifestyle – eating well, staying active, not smoking, and limiting alcohol – may lower your risk of some diseases.

Complications

If left untreated

• If the condition being investigated is not treated, it may progress – for example, a cancer could grow or spread, or an infection could become more serious.
• Delaying diagnosis after symptoms appear might mean that treatment is less effective.

Long-term outlook

For most people, a PET-CT scan provides important information that helps doctors plan the best treatment. Modern treatments are more effective than ever, and many conditions can be managed well when caught early. Your healthcare team will guide you every step of the way.

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