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Positron Emission Tomography / Computed Tomography Scan (PET/CT Scan)

What is Positron Emission Tomography Scan (PET Scan)?

PET is an advanced medical imaging modality which provides detailed information on the function of an organ or system in the body. PET scans are commonly used to evaluate and diagnose cancers, neurological disorders of the brain and cardiovascular diseases. The radiopharmaceutical is injected to patient’s body prior to the scan and images of the body are then acquired by a gamma camera in the PET scanner during the scan. The camera detects the photon emitted from the injected radiopharmaceutical in the body, and a multi-dimensional image of the examined body part will eventually be generated by the computer. The injected radiopharmaceutical usually accumulates in the diseased tissues more than the healthy tissues.

Fusion of PET and CT scans

PET has an innate pitfall that it is not able to locate the signals precisely, meaning that the emitted photons or signals from the patient’s body cannot be addressed to a precise location over the tissues or organs in the images. However, by incorporating the functional information acquired from the PET scan into the “anatomical map” provided by the CT scan, doctors will be able to understand the exact location and extent of the disease, and an effective treatment plan can then be formulated.


The whole examination lasts 3 to 4 hours. It starts with a simple interview consulted by the nurse, followed by a blood glucose level test, and then injection of radioactive isotope. After injection, you will be required to rest for about one hour to facilitate drug metabolism and absorption. The scan will then undergo for about 30 minutes. When the scan is over, rest for another 1-1.5 hours to allow the decay and further metabolism of the drug. Delayed scan may be performed if necessary.


  1. You should not receive any Barium examination within 10 days before the examination
  2. You need to keep fast for 6 hours before examination (except water). Avoid medication with high sugar level (e.g. cough syrup, glucose)
  3. On the day before examination, eat bland and easily digestible food
  4. On the day before examination, drink 6-8 glasses of water to ensure enough hydration of the body
  5. Avoid exercise and carrying weight one day before examination
  6. 6. Female patients who are pregnant or breastfeeding, patients with acute or continuous spasm, patients with unstable mental states, diabetics patients with uncontrollable blood glucose level are not suitable for the examination

For patients with diabetes mellitus (DM):

  1. Your PET scan will be scheduled in the morning (if possible) as this is the time most diabetic patients have the lowest blood glucose level.
  2. You should take your regular insulin or oral medications as usual the day before examination; After midnight, you should start fasting (except for water and non-diabetic medications).
  3. On the morning of the PET scan, please stop all insulin and oral medications.
  4. After completing the PET scan, you are encouraged to take a meal immediately. You may take half the usual regular insulin or regular dosage of oral medications with the post-PET meal to avoid the risk of hypoglycaemia.