PET scan

PET (positron emission tomography) scan is an imaging test that’s carried out by medical experts to check for diseases in your body. PET scan procedure involves the use of a special dye that contains radioactive tracers.

These dye can either be inhaled, swallowed, or injected into the body through the veins in the arm, depending on the area in the body that requires examination. Specific tissues and organs then absorb the tracer in the body.

When a PET scanner detects the tracer, it then sends images back, helping your doctor to see what might be wrong with your organs and tissues. About 2 million scans are performed every year in the United States alone.

The PET scan can be used to measure oxygen use, blood flow, the body’s use of sugar, and more. A PET scan is mainly an outpatient test. Meaning, a patient can go about their day when they are done with the procedure.

Why do a PET scan?

Your doctor may require a PET scan to give them information on your intake of oxygen, blood flow, or the metabolism of your tissues and organs.

PET scans are used to view complications at a cellular level, providing your doctor with the best view of complex systemic diseases.

PET scans are most mainly used to detect:

  • Heart Problems
  • Cancer
  • Brain disorders, such as complications with the central nervous system (CNS)

Heart problems

PET scans reveal areas of reduced blood flow in the heart. This is possible because a healthy heart tissue will absorb more of the tracer, while an unhealthy tissue will absorb less.

The different colors and degrees of brightness shown on the scan will reveal different levels of tissue function, thus, helping you and your medical doctor decide the next step forward.


The metabolic rate of cancer cells is higher when compared with non-cancerous cells. Cancer cells display as bright spots on the PET scan due to this high level of chemical activity. This is why PET scans help identify cancer in patients and also for;

  • Detecting how far cancer has spread
  • Checking if treatment for cancer is working
  • Checking if cancer has returned

Nonetheless, doctors may need to carefully read the result of these scans, as it is likely for non-cancerous conditions to appear as cancer on a scan. It is also possible for solid tumors not to show up on PET scans.

Brain disorders

Glucose is the primary fuel of the brain. Tracers are commonly attached to compounds like glucose during the procedure. By identifying radioactive glucose, the PET scan can spot what areas of the brain that are using glucose at maximum rates.

The result of the PET scan would be accessed by your doctor to check for the function of the brain and to identify any abnormalities.

Medical experts use PET scans to help analyze and manage several central nervous system (CNS) disorders, and some of them include:

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

How is the PET scan compare to other tests?

PET scans display metabolic changes happening at the cellular level in tissues or in an organ. This is essential because health complications often start from the cellular level. MRIs and CT scans do not show complications at the cellular level.

PET scans can be used to detect diseases at the very early stage of changes in the cells. MRIs and CT scans detect later changes, especially when a condition has altered the structure of tissues or organs in the body.

Recognition of illness at the cellular level provides your doctor with the best view of complex systemic diseases, such as:

  • Brain tumors
  • The CAD (Coronary artery disease)
  • Seizure disorders
  • Memory disorders

A CT scan uses a specific X-ray apparatus to produce images of inside the body. MRI scans, on the other hand, use radio frequency pulses and magnetic fields to form images of the internal structures like the bone, organs, and soft tissues.

When either the MRI or CT scan is performed and combined with a PET scan, the result given is known as “image fusion.”

A computer then combines the pictures from the two scans to form a 3D image. This provides your doctor with more information and gives room for a more precise diagnosis.

Risks associated with a PET scan

Although PET scan involves the use of radioactive tracers, but the chances of patients being exposed to harmful radiation are considered minimal. The volume of radiation in the tracer is less, so the body is at minimal risk of getting affected. It is still advisable to discuss the possible risks with your medical doctor.

The level of risk involved in the procedure is also minimal when compared with the benefits of the results that may reveal signs of underlying medical complications.

The tracer used is basically glucose combined with the radioactive component. This makes eliminating the tracers from the body easy, even when patients have a history of diabetes or kidney disease.

Patients with allergies and other health complications

Experiencing an allergic reaction to the tracers is possible. Patients should inform their doctors if they are allergic to aspartame, iodine, or saccharine.

Patients who can’t receive an iodine tracer may receive diluted barium tracers that are sweetened with saccharin.

People who are most likely to experience an allergic reaction to tracers made up of iodine include individuals with:

  • Asthma
  • Dehydration
  • Heart disease
  • History of allergic reactions to PET scans
  • Kidney disease
  • Blood cell disorders such as polycythemia vera, sickle cell anemia, and multiple myeloma

Pregnant women

Radiation is generally considered unsafe for developing fetuses. Patients should inform their doctors if they are pregnant or if they think they are pregnant before attempting a PET scan.

Preparing for a PET scan

Your doctor may provide complete information about how to prepare for a PET scan. It is advisable to inform your doctor about any supplemental medications and prescriptions that you’re taking.

A few days before your PET scan

You may be required to stop any strenuous physical activity, such as exercise, in the 24 to 48 hours before the test.

The day before your PET scan

You would be asked to maintain a low-carbohydrate, and sugar-free diet 24 hours before the procedure.

Beverages and foods that should be avoided also include;

  • Pasta
  • Cereal
  • Rice
  • Bread
  • Alcohol
  • Candy
  • Chewing gum
  • Dairy products
  • Caffeinated drinks
  • Fruits and fruit juices

Foods that can be eaten include tofu, meat, non-starchy vegetables, and nuts.

Hours before your PET scan

It’s not advisable to drink it eat anything the morning of your procedure, especially if you are receiving anesthesia. A few sips of water may be required if you have to take any meds.

In cases where anesthesia is not needed, you’d still need to avoid eating anything for at least 6 hours before your procedure.

Don’t also forget to avoid chewing on gums, licking cough drops, or sucking on candy. Water may be allowed, especially when you have to take any prescriptions.

Patients may be requested to change into a hospital gown. You may also be required to do away with any jewelry, and this includes body-piercings, because the testing equipment may be interfered with by metal.

How is a PET scan performed?

Before the procedure, you’ll get tracers through a that you’d be asked to drink, through a vein in your arm, or in a gas that you can inhale.

Patience is needed for your body to absorb the tracers fully. At least one hour is required before you can proceed with your scan.

The duration it takes for your body to completely absorb the tracer depends on what part of the body that needs scanning.

Movement needs to be restricted while waiting. It is crucial that you relax and do your best to stay warm. You’d have to avoid music, television, and reading if it’s a brain scan you’re undergoing.

The PET scan can last for 30 to 50 minutes, and it involves lying down on a narrow table that is attached to the PET machine. The table is designed in such a way that it slides upward for the scan to be conducted and downward for patients to step out.

While lying down, the technician would ask that you lay still. You may also be required to hold your breath for some seconds. You would hear clicking and buzzing sounds during the procedure.

You have nothing to worry about, as this is normal and part of the test. After all the images needed have been collected and recorded, the table would slide out, and that’s it.

What next after a PET scan?

After the PET scan, you are free to go about your day unless your doctor gives further instructions. Nevertheless, since radioactive residue is still in your body, you’d have to minimize your contact with infants and pregnant women for at least 24 hours.

Plenty of fluid should also be consumed to help flush out tracers in the body system. Naturally, it takes about two days for tracers to leave the body.

On the other hand, a trained specialist would interpret the images produced by the PET scan and relay the information to your doctor. The results of the test are usually ready within two working days, after which your doctor would inform you of the outcome of the procedure at your next appointment.

Have you ever had to do a PET scan before? What was the experience like for you? How efficient was the machine in helping with your medical issues? Share with us in the comments below.