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PET Scan

What is PET scan?

PET scan definition

The positron emission tomography (PET) is an imaging test that uses radioactive drugs (traces) to gives the detailed images, and functioning of internal anatomical structure and diseases. The PET scan can detect some diseases before they may appear in other imaging tests.

These radioactive traces given in the form of dye, they are administered into the body by swallowing, inhaling or injected intravenously, it depends on which organ or tissue of the body is being examined.

These traces collect in areas of the body that have higher chemical activity, which is important because certain tissue or organ of the body and certain diseases contain the higher level of the chemical activity. These areas are shown up as bright spots on a PET scan.

A PET scan in very useful for detecting cancer, evaluating several other conditions like brain disorders and heart disease. PET scan can create some special views if combined with CT scans and MRI scans.

A PET scan also measures the oxygen used, blood flow, how body use sugar and much more.

PET scan vs CT scan

A CT scan gives the detailed images of the internal anatomical structures by using x-rays and a PET scan detects if the proper functioning of the organ and tissue. The doctors sometimes recommend a combined PET-CT (Positron emission tomography and computer tomography) scan for the detection of the disease. A CT scan takes images by different angles using x-rays. For a PET the dye contains the radioactive traces are given to the patient. The dye contains radioactive sugar fluorodeoxyglucose-18 (FGD-18). The cells of your body absorb sugar and use more energy to pick up the sugar. The cancer cells used more energy than the normal cells. A PET scan show where the tracer is in the body. After that a computer gives the combined image of both CT and PET scan.

PET scan vs MRI

An MRI uses the electromagnetic waves to gives the image of internal anatomical structures. MRI is totally safe procedure. MRI is done in the case of cancer; tumors and some angiography procedures are also performed with the help of MRI scan these are called magnetic resonance angiography (MRA). A PET the dye contains the radioactive traces are given to the patient. The dye contains radioactive sugar fluorodeoxyglucose-18 (FGD-18). The cells of your body absorb sugar and use more energy to pick up the sugar. The cancer cells used more energy than the normal cells. A PET scan show where the tracer is in the body. After that a computer gives the combined image of both CT and PET scan.

What does a PET scan show?

A PET scan can show the blood flow, oxygen intake and metabolism in the cells. A PET scan can give results by showing a disease at the cellular levels. PET scan gives the best views of complex systemic disease.

A PET scan is commonly performed to detect:

  • Cancer
  • Heart disease
  • Brain disorders


The metabolic rate of cancer cells is higher than other normal cells. These cells have higher level of chemical activities so they show as bright spot on a PET scan. Because of this the PET scan are useful for

  • Detecting a cancer
  • To find if cancer has spread
  • To check whether a cancer treatment is working
  • To check the recurrence of cancer

There are also some cells show on the PET scan that looks like cancer but noncancerous. Many solid tumors also appear on the PET scan.

Heart disease

PET scan reveals the decrease blood flow in the heart. This is because a healthy heart tissue uses more of the tracers as compared to the unhealthy tissue.

Brain disorders

Brain is the source of glucose, during a PET scan the tracers attached to the compounds such as glucose. So, bi detecting the radioactive tracers PET scan detects the areas of the brain that utilizing glucose at highest levels.

PET scans are helpful to diagnose some brain disease like:

  • Alzheimer’s disease
  • Head trauma
  • Epilepsy
  • Depression
  • Parkinson disease

Risks involved with a PET scan:

The PET scan involved radioactive drugs (traces), but the radiation exposure is minimal during a PET scan. If the amount of radiation tracer is low than the risk is also low.

These traces contain sugar attached with radioactive compound so it eliminates easily from the human body.


Some people experience allergic reaction after injecting the tracer. If you are allergic to iodine, aspartame or saccharin tell your doctor.

People with these are more likely to have an iodine tracer allergic reaction:

  • History of allergic reaction to a PET scan
  • Asthma
  • Dehydration
  • Heart disease
  • Sickle cell anemia, polycythemia vera and multiple myeloma
  • Allergies
  • Kidney disease
  • Prescribed drugs like beta-blockers, nonsteroidal anti-inflammatory drugs NSAIDs, or interleukin-2 (IL-2)

The people who cannot have iodine tracer, they get tracer made up of diluted barium sweetened with saccharin.

Pregnant people

If you are going under a PET scan you will be get to exposed to radiation and radiation is harmful to the fetus. So, if you are pregnant you should not go for a PET scan

Other risks

People having kidney disorder and reduced creatinine levels.

You may feel discomfort if you claustrophobic.

Preparation for PET scan

Your doctor will give you all the instructions for how to prepare for the PET scan. Tell your doctor if:

  • You have ever had a bad allergic reaction
  • If you have diabetes
  • If you are pregnant or thinking you might be pregnant
  • If you are breast feeding
  • If you are claustrophobic

A few days before the PET scan you may be asked to avoid strenuous exercise for a few days before the study.


PET scan diet

PET scan diet before the day:

The day before the PET scan you’ll be asked to take a no-sugar diet and stick to a low-carbohydrate diet.

PET scan diet includes meat, nuts, tofu and non-starchy vegetables.

  • Food and beverage, you should avoid:
  • Bread
  • Rice
  • Pasta
  • Juices
  • Milk and yogurt
  • Fruits
  • Alcohol
  • Caffeinated beverage
  • Cereal
  • Candy, chewing gums

Preparation for a PET scan some hours before:

Don’t eat or drink anything on the entire day of your PET scan if you are taking anesthesia. You can drink few sips of water if you need to take any medications.

You have to take a fast for six hours if you are not receiving anesthesia.

You may ask to change into hospital gown before the procedure and remove all the metals.

You may be also asked to empty your bladder because it is approx. two hours long procedure but it is an outpatient procedure that means you don’t need to stay at night.

Procedure for PET scan:

Before the scan, the radioactive traces administered to your body by injecting it into your veins through your arm or through a solution you drink or a gas you inhale. After that you have to wait for approx. one hour because your body needs to take time to absorb the traces. It depends on the are to be scanned.

In the next PET scan procedure, you will undergo the scan, it may take up to 30 to 45 minutes. The PET scan machine is similar to the CT scan machine. You have to lie on the table during the whole scan. The technician will let you know that how many times you need to lie still and when to hold the breath. You may need to hold your breath for several seconds. When all the images recorded then you are asked to come out from the scan room.

After the procedure:

After the PET scan you can carry on your day as usual, unless your doctor gives any instructions.

The radioactive tracers will remain in the body for next 12 hours. Drink plenty of fluids after the PET scan to flush out the tracers from the body systems. Avoid your contact with pregnant women and infants for about 12 hours after the PET scan.


After the procedure the radiologist see the image and make reports according to the chemical activity of the of the tracers in your body. The radiologist may also compare the CT and MRI scans.