A type of imaging test, a PET (Positron Emission Tomography) scan can provide detailed information on the functioning of your tissues and organs. A small quantity of radioactive substance needs to be administered into your body to show the chemical activity.

The type of radioactive substance that will be used and how it will be administered will depend on the specific tissue or organ being targeted. The radioactive substance can be swallowed, inhaled or injected into a vein.

A larger amount of radioactive substances are absorbed in areas that have increased chemical activity. Areas where disease exists often have high chemical activity and these are displayed as bright spots on images generated through a PET scan. A variety of conditions such as heart disease, neurological problems and cancer can be examined in detail with the help of a PET scan.

Why is a PET scan conducted?

A PET scan provides an effective way to study the chemical activity in specific parts of your body. This can help diagnose abnormalities. PET scans are usually recommended for individuals diagnosed with cancer, brain disorders or heart disease.


A PET scan shows cancer cells as brighter spots since the metabolic rate of these cells is higher than normal cells. A PET scan can help in determining:

  • The spread and extent (stage) of certain types of cancers
  • Whether the cancer is responding adequately to treatment
  • Whether the cancer has resurfaced

PET scan results should be interpreted carefully because even non-cancerous diseases can have symptoms similar to cancer. Moreover, there are many forms of cancers that do not show up on PET scans. A PET scan can detect the following types of cancer.

Brain disorders

Regions inside the brain which are most active while performing specific tasks can be revealed through a PET scan. This imaging test can be used to examine a variety of brain abnormalities, for example:

  • Memory disorders
  • Seizures
  • Tumors

Heart disease

A PET scan can help detect areas with reduced blood flow inside the heart. This can help doctors to determine which specific areas inside the heart will benefit from coronary artery bypass surgery and angioplasty.


Radioactive material is used to conduct a PET scan, but it does not affect the functioning of other parts and processes of your body since radiation exposure levels are too low. However, the radiation can be harmful to the fetus of a pregnant woman or the child of a breast-feeding woman. Exposure risks to the fetus or infant need to be compared to the logic and benefits of performing a PET scan.

How to prepare

PET scans are generally carried out in an outpatient setting. Detailed instructions on how to prepare yourself will be provided to you by the doctor. Prior to the scan, make sure that you inform the doctor about any over-the-counter or prescription drugs, or vitamins or herbal supplements that you might be taking. In case you take certain types of medications or if you have conditions such as diabetes, you will be provided specific instructions prior to the scan.

Typically, you will be required to fast for several hours prior to the scan. You need to be in comfortable clothing when you go for your appointment. The health care team may ask you to remove your clothing and put on a hospital gown. If the targeted site is an area near your bladder, a soft tube (catheter) may be passed into your urethra in order to drain out the urine during the scan.

In case you are pregnant or if you suspect a pregnancy, inform your doctor beforehand. The fetus may be exposed to radioactive material used during the procedure. Tell your doctor in case you are breast-feeding your child. Your child faces radiation exposure risks through your breast milk.

What can you expect?

The PET scanner comprises of a large doughnut-shaped machine, similar to the computerized tomography (CT) scanner.

During the scan

Whether you swallow, inhale or are administered the radioactive material intravenously will depend on the specific organ being examined. In case the material is injected intravenously, you may briefly experience a cold sensation traveling up your arm.

You will be required to wait for at least 30-60 minutes to allow the radioactive material to be absorbed in the tissue or organ being targeted. Thereafter, you will have to lie down on a narrow table that slowly moves inside the PET scanner’s opening. Although the test is a painless procedure, you need to lie very still because images may get blurred due to movement. The test duration is around 30 minutes.

In case you are claustrophobic, you may experience some anxiety when you are positioned inside the scan machine. If you experience any discomfort, make sure you inform the technologist or the nurse. Certain medications can help you achieve a more relaxed state.

After the test

After the test, you may not have to restrict yourself on any of your daily routines. However, make sure that you increase your fluid intake in order to remove the radioactive material from your body.

Images generated by a PET machine have varying colors or degrees of brightness that represent the various levels of organ and tissue function. The images are evaluated by a radiologist who has special training in interpreting PET scans.

Images generated from other tests such as Magnetic Resonance Imaging (MRI) or Computerized Tomography (CT) can be compared or may also be combined with your PET scan images. A number of hospitals have special machines that can simultaneously carry out a PET and a CT scan. The images thus generated usually provide improved clarity.

Comparison of CT and integrated PET-CT based radiation therapy planning in patients with malignant pleural mesothelioma