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Positron emission tomography (PET) scan

A positron emission tomography (PET) scan is an imaging test that helps reveal how your tissues and organs are functioning. A PET scan uses a radioactive drug (tracer) to show this activity.

The tracer may be injected, swallowed or inhaled, depending on which organ or tissue is being studied by the PET scan. The tracer collects in areas of your body that have higher levels of chemical activity, which often correspond to areas of disease. On a PET scan, these areas show up as bright spots.

A PET scan is useful in revealing or evaluating several conditions, including some cancers, heart disease and brain disorders.

Why it's done Risks How you prepare What you can expect Results

PET scan is an effective procedure, which assists in detecting chemical activity levels in the body.  It is helpful in ruling out various disorders in brain and heart, including cancers. It is quite different from CT-scan (Computerized Tomography) and MRI (Magnetic Resonance Imaging), as it helps doctors to figure out problems effectively, providing detailed images and body functioning of the patient.  There can be multiple conditions, which can be diagnosed using the PET scans. Some of the disease conditions are as mentioned.

Brain Disorders: Multiple brain disorders including

Cancer Cells:

Cancerous lesions are seen as bright spots in a PET scan as the cancer cells have high levels of metabolic rate as compared to the normal cells. Thus the PET scans are helpful in the following scenarios:

  • Examining cancerous lesions
  • Finding out if the cancer has spread or multiplied
  • Examining relapse or progression of disease on treatment (effective or non- effective)
  • Cancer recurrences

It is very important to read the findings on a PET scan very carefully, as PET scans may sometimes show non-cancerous cells as cancers (malignant) or cancer cells as non-cancerous lesion (Benign). There can be multiple types of cancers, which can be detected and diagnosed by PET scans. Some of these are highlighted below.

  • Breast cancer
  • Brain cancer
  • Lung cancer
  • Esophageal cancer
  • Cervical cancer
  • Colorectal cancer
  • Lymphoma
  • Melanoma
  • Head
  • Neck
  • Thyroid
  • Prostate
  • Pancreatic


Heart disorders: Multiple different types of heart related disorders can be diagnosed with PET scans. Some of these disorders include.


  • Examine decreased blood flow in the arteries
  • Overall blood circulation
  • Detect blocked arteries (deposition of cholesterol or calcium)
  • Examine progression of any treatment done by the doctor (effective or non-effective) e.g. coronary artery bypass surgery or angioplasty (open blocked arteries).
  • Cardiomegaly (enlarged heart)
  • Valve abnormalities of the heart either structural or functional.


For your PET scan, a radioactive drug (tracer) will be put into your body. The amount of radiation you're exposed to is small, and the risk of negative effects from it is low. But the tracer might:

  • Cause a major allergic reaction, in rare instances
  • Expose your unborn baby to radiation if you are pregnant
  • Expose your child to radiation if you are breast-feeding

Talk with your doctor about the benefits and risks of a PET scan.

Tell your doctor:

  • If you've ever had a bad allergic reaction
  • If you've been sick recently or you have another medical condition, such as diabetes
  • If you're taking any medications, vitamins or herbal supplements
  • If you're pregnant or think you might be pregnant
  • If you're breast-feeding
  • If you're afraid of enclosed spaces (claustrophobic)

Your doctor will give you detailed instructions on how to prepare for your scan. A general rule is to avoid strenuous exercise for a couple of days before the study and to stop eating a few hours before the scan.

During the procedure:

  • The PET scan machine is similar to a CT-Scan machine. In terms of shape, the machine is donut shaped or big hollow circular shaped.
  • The procedure takes around 2 hours to complete and no hospitalization or admission is required and the procedure can be performed in an out-patient facility in the radiology Department.
  • During the procedure, a radioactive drug known as tracer is given to the patient. It can either be inhaled, swallowed or injected, depending upon the tissue or organ to be examined.
  • The patient is then asked to wait for about 60 minutes for the tracer to get absorbed in the body.
  • Further, the patient is asked to lie down on a thin padded examination table, which slides into the scanner.
  • The patient is asked to stay still during the scan, as the images from the scan can get blurred, if the patient moves during the scan. This step takes approximately 30 minutes to complete.
  • During the scan, the PET scan machine makes a buzzing, clicking sounds but this will not harm the patient at all.
  • The PET scan is a painless procedure. However, the patient might feel a little anxiety while in the scanner especially if the patient is claustrophobic. However, if the discomfort level increases, the patient must inform the technician or nurse. In such cases, a drug can be given to calm the patient.
  • Sometimes, the patient might be advised to undergo both CT- scan as well as PET scan. In such cases, the CT-scan will be done first and will be followed by PET scan.
  • The images captured during the scan are sent to the lab for further interpretation.


After the procedure:

After the procedure, the patient is asked to change into normal clothes and is advised to drink plenty of water/fluids in order to flush out or remove the tracer from the body. The patient can go home after the PET scan is performed and resume normal routine activities. The patient can drink and eat normally after the PET scan procedure is complete.

The nuclear physician interprets the images from the scan and prepares the report, which will further be handed over to the concerned doctor. The doctor examines the report carefully and discusses the results with the patient in detail. If the report is normal, it means the patient is fit and healthy with no abnormality detected. If the report is abnormal, it means that there are some abnormalities, which would need the attention of the doctor. The cancerous cells appear as bright spots in the image. The bright spots indicate cancer cells with high metabolic activity.

If a CT-scan was also advised, then the images of the CT scan will also be provided to the doctor after the procedure. PET scan is a very useful procedure and helps in early diagnosis of various problems, especially cancer related issues. Abnormal test results may indicate some of the following problems:

  • Any type of cancer (of any body part)
  • Infections
  • Structural and functional problems with any body organ.

Pictures from a PET scan display bright spots where the radioactive tracer collected. These spots reveal higher levels of chemical activity and details about how your tissues and organs are functioning. A doctor specially trained to interpret scan images (radiologist) will report the findings to your doctor.

The radiologist may also compare your PET images with images from other tests you've undergone recently, such as computerized tomography (CT) or magnetic resonance imaging (MRI). Or the pictures may be combined to provide more detail about your condition.



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