Definition & Overview

A positron emission tomography scan or PET scan is an imaging test used to help evaluate the functions of different organs and tissues. It uses nuclear or radioactive material (called a radiotracer) to provide imaging feedback into a special computer.

Physicians use the results of the PET scan to measure several physiological functions. These include oxygen use, sugar metabolism, blood flow, and even inflammatory responses. The test uses radiotracers to emit gamma rays, a special camera, and a computer to record and analyse data. Its goal is to identify any changes or deviations at the cellular level that could indicate the onset of a disease or medical condition. This early detection is crucial for the successful management and treatment of various conditions.

In some cases, the results of positron emission tomography are superimposed with computed tomography results (PET CT scan) to provide more precise diagnoses and detailed information that may not be available in other tests such as magnetic resonance imaging (MRI). The specific location of the anatomic anomaly is also easier to determine with combined imaging tests.

Who Should Undergo and Expected Results

There are a lot of uses for positron emission tomography scans. In oncology, a person with close relatives diagnosed with cancer can be offered this test for early detection. A PET scan for cancer can also be advised after cancer diagnosis to determine if the cancer has spread in the body. Those who underwent cancer treatments can also be asked to undergo a PET scan cancer to see if the treatment has been effective or, in the case of those going into remission, if cancer has returned or recurred.

Patients with different heart conditions are also eligible to undergo the test. Aside from determining early signs of heart disease, the test can also evaluate the impact of a heart attack on the muscles and tissues of the heart. Some physicians would also order a PET scan to help determine if the patient is suitable for coronary bypass surgery and other related heart procedures.

For those suffering from brain seizures or memory disorders, a PET scan can be helpful in mapping out the brain function to determine where an abnormality might occur. This technology is especially useful for those diagnosed with brain tumours and Alzheimer’s disease.

PET scan results can also be used to develop specialised and more effective treatment approaches for different individuals with varied conditions.

Because of the use of low-level radioactive materials, pregnant and breastfeeding women are not advised to undergo this test. It is also not recommended for diabetic patients with uncontrolled blood sugar levels and those who recently underwent radioactive therapy.

Positron emission tomography scanning is also an important tool in medical research. It has been used on research subjects to evaluate the function of skeletal muscles at rest and during physical activities.

The procedure is relatively simple and patients are not required to stay in the hospital. They can also resume normal activities after the scan. The radioactive tracers inside the body are processed naturally and passed through urine or stool a few days after the procedure. Patients are advised to drink plenty of fluids to help hasten this process.

The results of the PET scans are sent to specialists for interpretation. The patient would be asked to make a follow-up visit with their physician a few days after the scan to discuss the results.

How is the Procedure Performed?

There are several ways of introducing the radiotracer into the body. An intravenous catheter may be inserted into a vein of the hand or arm or the patient may be asked to swallow the radiotracer. In some cases, the radiotracer is in gas form and inhaled by the patient.

The physician will have to wait for about an hour for the radiotracer to be absorbed by the affected organ or tissue. A contrast material may be offered in liquid form. This material will settle in the intestines and provide additional reference for the test.

After the radiotracer has travelled to the rest of the body, the patient will be placed inside the PET scan machine. Patients have to stay still during the scan, which can last from several minutes to several hours, depending on condition being tested and the type of radiotracers being used.

After the PET scan, the intravenous catheter is removed and the patient is allowed to go home.

Possible Risks and Complications

Some patients may experience soreness and redness at the injection site where the catheter was inserted.

In rare cases, the patient may exhibit allergic reactions to the radiotracer. Women who are unknowingly pregnant may expose their unborn child to mild dosage of radiation.


  • Positron emission tomography — Computed tomography (PET/CT). Radiological Society of North America.

  • Mitchell CR, et al. Operational characteristics of (11)c-choline positron emission tomography/computerized tomography for prostate cancer with biochemical recurrence after initial treatment. Journal of Urology. 2013;189:1308.

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