What should you know about PET-CT scan contrast?

The PET part follows a small amount of radioactive sugar-like material, often called an FDG tracer, as it moves through the body. The CT part creates detailed pictures of organs and tissues. Some examinations add contrast to make certain structures easier to distinguish. Contrast may be swallowed or given through a vein, depending on the scan plan. The tracer and contrast are different substances with different jobs.

Tell the imaging team about previous reactions to contrast, kidney problems, diabetes, pregnancy, breastfeeding, and medicines or supplements. These details can affect preparation and whether a particular contrast agent is suitable. A warm feeling or unusual taste can occur with injected contrast, but report any new symptom during the appointment.

Follow the centre’s instructions about fasting, drinking water, medicines, and activity. Avoid strenuous exercise beforehand if instructed, because muscle activity can affect the images. Wear comfortable clothing and remove metal objects when asked. After the tracer is given, you may rest quietly before imaging; remaining still helps the pictures remain clear. Ask whether you should arrange transport or limit close contact with young children or pregnant people for a short period after the scan.

Tell staff immediately if you develop trouble breathing, swelling of the face or throat, widespread itching, dizziness, or severe weakness during or soon after contrast. Seek urgent medical help for breathing difficulty, fainting, or rapidly worsening symptoms. Mild soreness at an injection site can be monitored, but contact the imaging service if it becomes increasingly painful, swollen, or discoloured.

Ask which tracer and contrast, if any, are planned; whether you need to fast; how diabetes medicines should be handled; when results will be discussed; and what to do if a past contrast reaction is relevant.