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Positron Emission Tomography-Computed Tomography, also known as Positron Emission Tomography or PET-CT scan, can display the metabolic state of cells in various parts of the body and check important body functions such as blood flow, oxygen use, and the glucose metabolism of organs. Through the use of 3D colour images and a radioactive material, a PET-CT can pinpoint abnormal metabolic activity in organs and tissues and evaluate how well they are functioning.


Positron emission tomography (PET) is particularly useful in the diagnosis of malignant tumours as most malignant tumours exhibit high metabolic rates and rapid cell division. Its clinical purpose includes:

  • Detecting cancer at an early stage
  • Determining whether a tumour is malignant
  • Determining whether a cancer has spread in the body
  • Identifying the source of a cancer
  • Formulating a treatment plan
  • Evaluating the effectiveness of treatment

Information on the side effects of Positron Emission Tomography (PET), the latest technologies, and services we provide follow below.

Who is applicable for Positron Emission Tomography (PET-CT)?

Positron emission tomography (PET-CT) scans for cancer, assesses whether cancer cells have spread in the body, evaluates the treatment outcome, and detects whether cancer recurrence after treatment. It can also be used to locate infection sites in diseases of the heart or brain. It is often used to investigate epilepsy, Alzheimer’s disease, cancer, and heart disease. One special type of PET scan is PSMA, which stands for Prostate Specific Membrane Antigen. Due to the available clarity, it can identify suspicious lesions for prostate cancer with very low levels of prostate specific antigen and offers a more accurate evaluation from being able to assess the prostate area, as well as the lymph glands and bones.


Before receiving PET-CT, patients are injected with a small amount of radioactive substance, which includes the most commonly used (2-[Fluorine-18]fluoro-2-deoxy-D-glucose, FDG). This will accumulate in the lesion tissue and provide three-dimensional colour images to accurately detect the location of the lesion, together with combined images from PET-CT and computer scanning. This technique is often used to complement X-rays or MRI to provide more insight into the disease and evaluate prognosis of the tumour in the early and late stages of cancer treatments.

What are the side effects of PET-CT?

Radioactive substances and isotopes used in PET-CT are discharged from the human body within a short period. The amount of radiation produced by PET-CT is minimal, and the scanning process causes no pain. It is safe and rarely associated with any significant side effects. After receiving the examination, it is recommended that patients drink plenty of water to help flush out the radioactive substance from their bodies.
However, the side effects of PET-CT on children and with pregnant women have not been studied. Therefore, close contact with children under 5 years old and pregnant women should be avoided within 24 hours after the examination. If you are pregnant or breastfeeding at the time, you are advised not to take the PET-CT so as to avoid potential risk to the foetus or infant.

A PET-CT scan takes about 1 to 2 hours and the procedure is as follows:

  1. You will be changed into a gown for the examination.
  2. Your height, weight, blood pressure, and blood sugar levels will be measured.
  3. We will enquire into your family history and personal medical history.
  4. You will receive an isotope intravenous injection (e.g. F18-FDG glucose*, C11 acetate**).
  5. You then need to rest for about 60 minutes.
  6. You will then need to urinate as much as possible prior to the scan.
  7. The scan itself will need about 15 to 20 minutes. Where you should lie down, relax and breathe normally.
  8. If necessary, you may also be given an injection of contrast media.
  9. You may rest in the lounge after the examination.

*18-F FDG is a type of glucose and is the most common radiopharmaceutical used in PET scan. An FDG PET scan can assess the presence, location and severity of cancers. Glucose is a common substance that every cell in your body needs in order to function and therefore will be taken up by cells. Diabetic patients do not need to worry; it would take 4,000 doses of FDG to equal the glucose in 1 teaspoon of sugar. FDG has a half-life of approximately 110 minutes, so it is quickly expelled from your body.
** C-11 Acetate is another radiopharmaceutical that is used in PET scans. It is particularly useful in imaging liver cancer, low grade lymphoma, and prostate cancer. If a dual-tracer (C-11 Acetate + 18-F FDG) scan is necessary, the patient will receive another dose of 18-F FDG after the C-11 Acetate scan is completed, and the 18-F FDG scan will then be carried out.

Are there any other diagnostic alternatives to PET-CT?

Positron emission tomography (PET-CT) is not the only diagnostic service. The specific features of the various medical screening, imaging/diagnostic and interventional services do vary. Patients should consult their doctor and choose the most suitable check-up plan for their requirements. Understand more


Advantages:X-rays clearly show a detailed outline of the organs in the body.

Application on Cancer Treatment:Breast cancer screening and diagnosis, including computer-reconstructed 3D mammography

Radiation:Minimal radiation exposure


Advantages:Immediate changes in the organs can be seen with ultrasound. However, the ability to penetrate the bones, tissues along with the image resolution is limited.

Application on Cancer Treatment:Cancer screening, such as prostate ultrasound and bladder ultrasound

Radiation:No ionizing radiation


Advantages:The whole body may be scanned by CT by producing hundreds of cross-sectional images to form two-dimensional and three-dimensional images.

Application on Cancer Treatment:Multiple cancer diagnoses

Radiation:Radiation is stronger than X-ray, but in recent years, low-dose Computed Tomography (CT) technology has been developed.

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Advantages:PET-CT is able to improve the accuracy of anatomical imaging by using 3D colour images and data from computer scanning.

Application on Cancer Treatment:Early-staged tumour diagnosis, Malignant tumour differentiation, Determine cancer staging and Monitor the effectiveness of treatment

Radiation:The latest ASIR low-radiation technology can reduce radiation dose by 50% compared with traditional PET-CT scanning.
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Advantages:With MRI, the morphology of the soft tissues and nerve veins are presented with extremely high image contrast.

Application on Cancer Treatment:Diagnose the location of the tumours and the development of the tumours

Radiation:No ionizing radiation

Our centre’s services

  • 3D Mammogram Services
  • Computed Tomography (CT)
  • Positron Emission Tomography–Computed Tomography (PET-CT)
  • 3 in 1 – PET and CT and MRI
  • Ultrasound Check-up


  1. St. Teresa’s Hospital, 正電子電腦掃描 – 常見問題 http://www.sthscan.com/?page=petfaq&lang=zh