Before the Scan Day
When your PET CT scan is booked, the clinic will provide specific preparation instructions. Following these instructions carefully helps ensure the images are as clear and accurate as possible.
Fasting: For most PET CT scans using the FDG tracer, you will be asked to fast for 4 to 6 hours before the appointment. This means no food, no sugary drinks, and no sweets. Water is usually allowed and encouraged. Fasting keeps your blood sugar levels stable, which helps the tracer distribute properly.
Hydration: Drinking plenty of water in the 24 hours before the scan is helpful. Good hydration supports tracer clearance and produces clearer images. Stick to plain water rather than juices or flavoured drinks.
Exercise: Avoid strenuous physical activity for 24 hours before the scan. Active muscles take up more of the FDG tracer, which can create false signals on the images and make interpretation more difficult.
Medications and Medical Conditions
Diabetes: If you have diabetes, inform the team when the scan is booked. Blood sugar levels affect FDG uptake, so the team may give you specific instructions about your diabetes medications and meal timing. Do not adjust your medications on your own without guidance from the medical team.
Other medications: Most regular medications can be taken as usual with a small sip of water. However, let the team know about all medications you are taking, as some may require adjustments.
Pregnancy and breastfeeding: If you are pregnant, suspect you might be, or are breastfeeding, tell the team immediately. The scan involves radiation, and special precautions or alternative arrangements may be needed.
Allergies: The radioactive tracer used in PET CT is different from the contrast dye used in some CT scans. Allergic reactions to PET tracers are extremely rare. If you have had reactions to contrast agents in the past, mention this to the team.
On the Day of the Scan
Arrival: Arrive at the time given by the clinic. You may need to complete some paperwork and have your blood sugar checked (especially if you have diabetes).
Tracer injection: A small amount of the radioactive tracer will be injected into a vein in your arm. The injection feels similar to a standard blood draw.
Resting period: After the injection, you will rest quietly for about 45 to 60 minutes while the tracer distributes through your body. During this time, try to stay still and relaxed. Avoid talking excessively, chewing gum, or using your phone extensively, as these activities involve muscle movement that can affect the images.
The scan: You will lie on a narrow table that moves slowly through the scanner. The machine is ring-shaped and open at both ends. The scan itself takes about 20 to 30 minutes. You need to lie still during this time, but you will not feel anything.
After the Scan
Once the scan is complete, you can resume your normal activities, including eating and drinking. The tracer leaves your body naturally through urine, so drinking extra water after the scan helps flush it out faster.
The radiation from the tracer is low and decreases rapidly. As a general precaution, you may be advised to avoid prolonged close contact with young children and pregnant women for several hours after the scan.
Results are typically available within a few days, depending on the centre. The nuclear medicine physician prepares a report that is sent to your referring doctor, who will discuss the findings with you.
Questions to Ask Before Your Scan
If anything is unclear about your preparation instructions, call the clinic and ask. Good questions include: How long should I fast? Should I take my usual medications? How long will the entire visit take? When can I expect my results? Your care team is there to help you feel prepared and comfortable.