Log In Start studying!

Select your language

Suggested languages for you:
StudySmarter - The all-in-one study app.
4.8 • +11k Ratings
More than 3 Million Downloads
Free
|
|
PET Scan

Have you suffered from a bone injury before? Did you get an X-ray taken? An X-ray would show structures like bones inside your body, and a doctor might use this information to diagnose bone-related injuries like fractures.

If we can see our bones through an X-ray, is there a way to see how much blood is flowing to our heart or how much oxygen is being used in our brain? A PET scan allows us to get this kind of information, and doctors would use this for various reasons, including diagnosing cancer.

  • First, we will discuss what a PET scan is and how it is typically used in different fields.
  • Then, we will distinguish between a PET scan and another imaging procedure called a CT scan.
  • Finally, we will discuss some risks and considerations related to the PET scan.

PET Scan Meaning

Let's start by looking at the meaning of PET scan. A positron emission tomography (PET) scan is an imaging test that uses radioactive substances called tracers to examine blood flow, metabolism, and chemical composition (for example, oxygen concentration) in specific body tissues or organs.

It is a procedure that is typically performed to identify specific conditions or assess how the treatment of certain diseases is working.

Radioactive tracers (also known as radiotracers or radionuclide) are substances that give off particles called positrons which react with negatively charged particles called electrons in the body, producing a tiny amount of energy that is detected by a PET scanner to create images of organs and tissue.

Metabolism refers to the life-sustaining chemical reactions that take place in living cells that either consume or produce energy.

PET Scan Procedures and Interpretation

A small amount of tracer is either injected into a patient intravenously (through a vein), swallowed, or inhaled, depending on what area of the body is being examined. After some time, the tracer would be distributed throughout the body and retained in bodily tissues with a lot of cell activity.

The patient would lie down and slide through the central hole of the PET scanner (Fig. 1). Then, the PET scanner would be positioned at the region of the body that will be scanned.

The PET scanner has a special type of camera that detects positrons released by the tracer in the organ or tissue under study. A computer reconstructs the signals into three-dimensional images and displays them on a monitor.

The radioactive tracers attach to a chemical substance–such as glucose, carbon, or oxygen–that a specific organ or tissue uses during metabolism.

For example, glucose is widely used for metabolic processes in the body. In examining the brain using a PET scan, a radioactive substance is added to glucose, forming a radioisotope called fluorodeoxyglucose (FDG). PET scanning typically uses FDG.

The specific tracer used during the procedure depends on the target organ or tissue. For example, suppose the PET scan aims to look at blood flow and circulation in an organ. In that case, the radionuclide is likely a type of radioactive oxygen, carbon, nitrogen, or gallium.

The first images taken by the PET scanner are used to determine if the machine is positioned correctly. To avoid producing blurry photos and causing errors, the patient must stay still and even hold their breath. The scan can take 30 minutes to an hour, depending on the body part being scanned.

When the images are taken, areas with higher uptake and brighter spots would generally be interpreted as having more activity.

For example, cancer cells typically consume a lot of sugar and appear as bright patches (dubbed "hot spots") on a PET scan. On the other hand, heart tissue that has been damaged will be less active and will consume less sugar. As a result, it would be visible as a darker area compared to normal heart tissue.

PET Scan vs. CT Scan

If you have seen some medical dramas on TV, you may have heard of another imaging procedure called the CT scan.

The computed tomography (CT) scan is a computerized imaging procedure that directs a beam of X-rays toward a patient and rotates it around the body.

Signals produced by this procedure are processed by a computer, generating cross-sectional images of the body. Once it has collected enough photos, the computer stacks these together to form a three-dimensional image of the patient.

While the CT scan shows detailed cross-section images of the organs and tissues of the body, the PET scan shows the activities within these organs and tissues (Fig. 2).

Some machines combine the PET scan with a CT scan, and these are called PET-CT. A PET-CT scan would provide more definitive information about the metabolic changes and their locations in the body.

How a PET Scan is Used to Detect Various Types of Diseases

A PET scan is typically performed to assess organs or tissues for the presence of diseases or other conditions. However, there are other reasons for administering a PET scan, including:

  • Diagnosing neurological conditions like Alzheimer's disease, epilepsy, and stroke.

  • Locating cancerous regions that need to be treated during brain surgery.

  • Detecting how cancer is spreading from the original site to other parts of the body.

  • Assessing blood flow to the heart to determine if there is a need for treatment.

  • Evaluating the effectiveness of cancer treatment.

  • Verifying lesions or masses in the lungs that were detected in a chest x-ray or chest CT scan.

  • Mapping normal human brain and heart function.

Let's look at how a PET scan would be administered and interpreted.

Fluorine-18 (18F) fluoro-deoxyglucose (FDG), often referred to as [18F] FDG PET, is a tracer commonly used for cancer imaging. It is a compound resembling glucose, except its oxygen molecule is replaced with a positron-emitting Fluorine-18. FDG is taken up much like glucose, except it is trapped and retained in tumors after being phosphorylated by an enzyme called hexokinase.

Due to the high metabolic activity in cancerous tissues, a significant amount of glucose is absorbed there. This means that 18F-FDG is also taken up heavily in these areas, resulting in a bright spot on the PET scan.

In this way, FDG PET can be used to diagnose, stage, and monitor cancers, most notably Hodgkin's lymphoma, non-Hodgkin lymphoma, and lung cancer. On the other hand, given that Alzheimer's disease manifests in decreased glucose and oxygen metabolism in the brain, FDG PET can also be used to differentiate between Alzheimer's and other forms of dementia.

PET Scan Side Effects and Other Considerations

A PET scan uses only a little amount of radiation, so there is no need to worry about radiation exposure; a PET scan typically exposes the patient to the same amount of radiation as a conventional CT scan. Moreover, the radiation does not stay in the patient's body for very long.

However, pregnant or breastfeeding women must notify their doctor before undergoing this test. Because their organs are still developing, infants developing in the womb are more vulnerable to the effects of radiation.

Some patients may also experience discomfort, redness, or swelling at the site where they got injected. There is also a small chance of an allergic reaction to the radioactive tracer. For this reason, it is vital to inform the healthcare provider about any allergies or sensitivities to medications, contrast dyes, iodine, or latex.

There is also a possibility of getting less accurate results from the PET scan due to certain factors or conditions, including:

  • High blood sugar or insulin levels in diabetics.

  • Medicines such as sedatives and tranquilizers.

  • Caffeine, alcohol, or tobacco consumption.

  • Excessive movement or inability to lie still.

PET Scan - Key takeaways

  • A positron emission tomography (PET) scan is an imaging test that uses radioactive tracers to examine blood flow, metabolism, and chemical composition in specific body tissues or organs.
  • A small amount of tracer is either injected into a patient intravenously (through a vein), swallowed, or inhaled, depending on what area of the body is being examined.
  • The PET scanner has a special type of camera that detects positrons released by the tracer in the organ or tissue under study.
  • While the CT scan shows detailed cross-section images of the organs and tissues of the body, the PET scan shows the activities within these organs and tissues.

References

  1. Kapoor, Mayank, and Anup Kasi. “PET Scanning - StatPearls - NCBI Bookshelf.” PET Scanning - StatPearls - NCBI Bookshelf, 9 Oct. 2021, www.ncbi.nlm.nih.gov/books/NBK559089.
  2. “PET Scan: MedlinePlus Medical Encyclopedia.” PET Scan: MedlinePlus Medical Encyclopedia, medlineplus.gov/ency/article/003827.htm. Accessed 7 Sept. 2022.
  3. “Positron Emission Tomography (PET) - Health Encyclopedia - University of Rochester Medical Center.” Positron Emission Tomography (PET) - Health Encyclopedia - University of Rochester Medical Center, www.urmc.rochester.edu/encyclopedia/content.aspx?contenttypeid=92&contentid=p07654. Accessed 7 Sept. 2022.
  4. “Lung PET Scan: MedlinePlus Medical Encyclopedia.” Lung PET Scan: MedlinePlus Medical Encyclopedia, cybercemetery.unt.edu/archive/oilspill/20120924205035/http://www.nlm.nih.gov/medlineplus/ency/article/007342.htm. Accessed 7 Sept. 2022.
  5. Johan Vansteenkiste, Christophe Dooms, Jokke Wynants, Chapter 2 - PET Imaging, Editor(s): Richard K. Albert, Stephen G. Spiro, James R. Jett, Clinical Respiratory Medicine (Third Edition), Mosby, 2008, Pages 69-78, ISBN 9780323048255, https://doi.org/10.1016/B978-032304825-5.10002-9. (https://www.sciencedirect.com/science/article/pii/B9780323048255100029)
  6. “Computed Tomography (CT).” Computed Tomography (CT), www.nibib.nih.gov/science-education/science-topics/computed-tomography-ct. Accessed 7 Sept. 2022.
  7. “Computed Tomography (CT).” Computed Tomography (CT), www.nibib.nih.gov/science-education/science-topics/computed-tomography-ct. Accessed 7 Sept. 2022.
  8. DeBerardinis, Ralph J., and Craig B. Thompson. “Cellular Metabolism and Disease: What Do Metabolic Outliers Teach Us? - PMC.” PubMed Central (PMC), www.ncbi.nlm.nih.gov/pmc/articles/PMC3337773. Accessed 7 Sept. 2022.

Frequently Asked Questions about PET Scan

A PET scan is used to assess organs or tissues for the presence of diseases and other conditions, including cancer.

A PET scan is an imaging test that uses radioactive substances called tracers to examine blood flow, metabolism, and chemical composition in specific body tissues or organs.

While the CT scan shows detailed cross-section images of the organs and tissues of the body, the PET scan shows the activities within these organs and tissues

A PET scan shows blood flow, metabolism, and chemical composition in specific body tissues or organs

A PET scan involves different types of tracers depending on the objective of the procedure. For example, suppose the PET scan aims to look at blood flow and circulation in an organ. In that case, the radionuclide is likely a type of radioactive oxygen, carbon, nitrogen, or gallium. 

Final PET Scan Quiz

Question

What does PET in PET scan stand for?

Show answer

Answer

Positron emission tomography

Show question

Question

What is a PET scan?

Show answer

Answer

A PET scan is an imaging test that uses radioactive tracers to examine blood flow, metabolism, and chemical composition in specific body tissues or organs. 

Show question

Question

What do you call the radioactive substance injected into or swallowed/inhaled by  a patient undergoing a PET scan?

Show answer

Answer

Tracer

Show question

Question

______ refers to the life-sustaining chemical reactions that take place in living cells that either consume or produce energy.

Show answer

Answer

Metabolism

Show question

Question

What happens to the tracer after it is administered to the patient?

Show answer

Answer

After some time, the tracer would be distributed throughout the body and retained in bodily tissues with a lot of cell activity.

Show question

Question

The tracer releases _____ in the organ or tissue under study.

Show answer

Answer

Positrons

Show question

Question

What do we mean by "hot spots" in a PET scan?

Show answer

Answer

Hot spots are bright patches on a PET scan, indicating higher levels of activity.

Show question

Question

Heart tissue that has been damaged will be less active and will consume less sugar. As a result, on a PET scan it would be visible as a ____ area compared to normal heart tissue.

Show answer

Answer

darker

Show question

Question

Distinguish a CT scan from a PET scan.

Show answer

Answer

While the CT scan shows detailed cross-section images of the organs and tissues of the body, the PET scan shows the activities within these organs and tissues.

Show question

Question

What is the purpose of a PET scan?

Show answer

Answer

A PET scan is typically performed to assess organs or tissues for the presence of diseases or other conditions.

Show question

Question

Does a patient need to worry about radiation exposure after a PET scan? Why or why not?

Show answer

Answer

A PET scan uses only a little amount of radiation, so there is no need to worry about radiation exposure; a PET scan typically exposes the patient to the same amount of radiation as a conventional CT scan. Moreover, the radiation does not stay in the patient's body for very long. 

Show question

Question

Describe how a PET scan works.

Show answer

Answer

A small amount of tracer is administered to a patient. After some time, the tracer would be distributed throughout the body and retained in bodily tissues with a lot of cell activity. The PET scanner has a special type of camera that detects positrons released by the tracer in the organ or tissue under study. 

A computer reconstructs the signals into three-dimensional images and displays them on a monitor. 



Show question

Question

Cancer cells typically consume a lot of sugar and appear as ______ on a PET scan. 

Show answer

Answer

bright patches

Show question

Question

The following are functions of a PET scan except for:

Show answer

Answer

Detecting how cancer is spreading from the original site to other parts of the body

Show question

Question

What is a PET-CT scan?

Show answer

Answer

Some machines combine the PET scan with a CT scan, and these are called PET-CT. A PET-CT scan would provide more definitive information about the metabolic changes and their locations in the body.

Show question

60%

of the users don't pass the PET Scan quiz! Will you pass the quiz?

Start Quiz

Discover the right content for your subjects

No need to cheat if you have everything you need to succeed! Packed into one app!

Study Plan

Be perfectly prepared on time with an individual plan.

Quizzes

Test your knowledge with gamified quizzes.

Flashcards

Create and find flashcards in record time.

Notes

Create beautiful notes faster than ever before.

Study Sets

Have all your study materials in one place.

Documents

Upload unlimited documents and save them online.

Study Analytics

Identify your study strength and weaknesses.

Weekly Goals

Set individual study goals and earn points reaching them.

Smart Reminders

Stop procrastinating with our study reminders.

Rewards

Earn points, unlock badges and level up while studying.

Magic Marker

Create flashcards in notes completely automatically.

Smart Formatting

Create the most beautiful study materials using our templates.

Sign up to highlight and take notes. It’s 100% free.