A Positron Emission Tomography or a PET scan, is an imaging test that is done to determine any disease conditions in the body. The scan uses a special dye containing radioactive tracers, which are either swallowed or inhaled, or injected into a vein in the arm depending on which region of the body is being examined. This scan helps the doctor to monitor how well organs and tissues are working. The dye gets collected in areas of higher chemical activity in the body.

PET scans reveal metabolic alterations that develop at the cellular level in an organ or tissue. This is vital because disease originates at the cell level, while CT scans and MRIs cannot diagnose problems at the cellular level. PET scans can determine even minute changes in the cells. However, CT and MRI scans can only evaluate changes that happen in the later stages, as diseases advance and alter the structure of the organs and tissues.

Also Read: Chest CT Scan For COVID-19: Know Who Should Get It And The Key Facts
Patient undergoing PET CT

Why It Is Done?

The doctor may suggest a person to get a PET scan to examine the blood flow, oxygen uptake, and the metabolism of organs and tissues. This scan shows any health issues that may develop at the cell level, which gives the doctor a clear-cut idea to assess complex systemic diseases.

PET scans are performed to detect:


Heart problems

Brain disorders, including any problems with the central nervous system (CNS)


Generally, cancer cells have a higher metabolic rate than noncancerous cell due to a high level of chemical activity. The cancer cells show up as bright spots on PET scans and are useful for both detecting cancer and for:

To check if cancer has spread.

To see if cancer treatment is effective.

For monitoring any recurrence of cancer.

PET scan should always be carefully evaluated by a doctor, as there is a chance for noncancerous conditions to resemble cancer on a scan and it is also common for solid tumours to fail to show.

Also Read: 8 Signs Of Cancer: Early Detection Saves Lives

Heart Issues

PET scan discloses regions of decreased blood flow in the heart. Healthy heart tissue will usually take in more of the tracer than unhealthy tissue or tissue that has reduced blood flow.

Different colour ranges and degrees of brightness on the PET scan will help to determine levels of tissue function and help the doctor to plan for better treatment of the condition.

Brain Disorders

Glucose is the chief source of fuel for the brain. During the PET scan, tracers get attached to glucose compounds and by detecting radioactive glucose, the PET scan helps to determine which regions of the brain are using glucose at the highest rates. This test also helps the doctor to monitor how well the brain is working and detect any abnormalities. Furthermore, it is also used to diagnose and treat central nervous system disorders including:

Alzheimer’s disease



Head trauma

Parkinson’s disease    

How To Prepare For PET Scan?

The person going for a PET scan will be thoroughly instructed by the doctor on how to prepare for the PET scan.

A Few Days Before Scan:

You may be asked to limit from doing any strenuous physical activity like an exercise in the 24 to 48 hours prior to the test.

The Day Before Scan:

The day before the scan, you should have a low carb, no sugar diet.

Hours Before Scan:

You should avoid eating or drinking anything the morning before the PET scan and can only take a few sips of water if required to take any medications. You should not wear any jewellery or metal, including body-piercing jewel before the test as metal interferes with the testing machine.

Other Considerations

You should inform the doctor or healthcare provider about any existing medical conditions:

Pregnant women or those who suspect to be pregnant should inform the doctor as this test is unsafe for the foetus.

Lactating mothers should pump and store breastmilk 24 hours prior to the procedure, as they cannot breastfeed for 24 hours after the test.

Diabetic patients should be informed to take normal medications and eat a light meal 4 hours before the scheduled time for a PET scan.

How Is A PET Scan Performed?

Before the procedure you will be injected with a tracer through a vein in the arm or drinking a solution or in a gas, you inhale. The system needs time to absorb the tracers and you are made to wait for an hour before the scan.

The PET scan lasts for 30 to 45 minutes, the individual has to lie down on a narrow table attached to the machine. The table glides slowly into the machine so that the scan be done. Until the scan is completed, you should lie down still and need to hold breath for several seconds. You will be listening to buzzing and clicking noises during the scan. After all, images have taken, the patient will be slide out of the machine.

After The Test

After the test, the person can go about with routine work, unless the doctor gives you specific instructions. However, radioactive material will remain in the body for about 12 hours, where the person should limit contact with both pregnant women and infants during this time.

Additionally, you must be drinking plenty of fluids after the test to help remove tracers out of the body. Usually, it takes about 48 hours for tracers to completely flush out of the system. A trained specialist will interpret the PET scan images and the result will be provided within 24 hours.