Positron Emission Tomography (PET) (2023)

What is positron emission tomography (PET)?

Positron emission tomography (PET) is a type of nuclear medicine procedure that measures metabolic activity of the cells of body tissues. PET is actually a combination of nuclear medicine and biochemical analysis. Used mostly in patients with brain or heart conditions and cancer, PET helps to visualize the biochemical changes taking place in the body, such as the metabolism (the process by which cells change food into energy after food is digested and absorbed into the blood) of the heart muscle.

PET differs from other nuclear medicine examinations in that PET detects metabolism within body tissues, whereas other types of nuclear medicine examinations detect the amount of a radioactive substance collected in body tissue in a certain location to examine the tissue's function.

Since PET is a type of nuclear medicine procedure, this means that a tiny amount of a radioactive substance, called a radiopharmaceutical (radionuclide or radioactive tracer), is used during the procedure to assist in the examination of the tissue under study. Specifically, PET studies evaluate the metabolism of a particular organ or tissue, so that information about the physiology (functionality) and anatomy (structure) of the organ or tissue is evaluated, as well as its biochemical properties. Thus, PET may detect biochemical changes in an organ or tissue that can identify the onset of a disease process before anatomical changes related to the disease can be seen with other imaging processes such as computed tomography (CT) or magnetic resonance imaging (MRI).

PET is most often used by oncologists (doctors specializing in cancer treatment), neurologists and neurosurgeons (doctors specializing in treatment and surgery of the brain and nervous system), and cardiologists (doctors specializing in the treatment of the heart). However, as advances in PET technologies continue, this procedure is beginning to be used more widely in other areas.

PET may also be used in conjunction with other diagnostic tests, such as computed tomography (CT) or magnetic resonance imaging (MRI) to provide more definitive information about malignant (cancerous) tumors and other lesions. Newer technology combines PET and CT into one scanner, known as PET/CT. PET/CT shows particular promise in the diagnosis and treatment of lung cancer, evaluating epilepsy, Alzheimer's disease and coronary artery disease.

Originally, PET procedures were performed in dedicated PET centers, because the equipment to make the radiopharmaceuticals, including a cyclotron and a radiochemistry lab, had to be available, in addition to the PET scanner. Now, the radiopharmaceuticals are produced in many areas and are sent to PET centers, so that only the scanner is required to perform a PET scan.

Further increasing the availability of PET imaging is a technology called gamma camera systems (devices used to scan patients who have been injected with small amounts of radionuclides and currently in use with other nuclear medicine procedures). These systems have been adapted for use in PET scan procedures. The gamma camera system can complete a scan more quickly, and at less cost, than a traditional PET scan.

How does PET work?

PET works by using a scanning device (a machine with a large hole at its center) to detect photons (subatomic particles) emitted by a radionuclide in the organ or tissue being examined.

The radionuclides used in PET scans are made by attaching a radioactive atom to chemical substances that are used naturally by the particular organ or tissue during its metabolic process. For example, in PET scans of the brain, a radioactive atom is applied to glucose (blood sugar) to create a radionuclide called fluorodeoxyglucose (FDG), because the brain uses glucose for its metabolism. FDG is widely used in PET scanning.

Other substances may be used for PET scanning, depending on the purpose of the scan. If blood flow and perfusion of an organ or tissue is of interest, the radionuclide may be a type of radioactive oxygen, carbon, nitrogen, or gallium.

The radionuclide is administered into a vein through an intravenous (IV) line. Next, the PET scanner slowly moves over the part of the body being examined. Positrons are emitted by the breakdown of the radionuclide. Gamma rays called annihilation photons are created when positrons collide with electrons near the decay event. The scanner then detects the annihilation photons, which arrive at the detectors in coincidence at 180 degrees apart from one another. A computer analyzes those gamma rays and uses the information to create an image map of the organ or tissue being studied. The amount of the radionuclide collected in the tissue affects how brightly the tissue appears on the image, and indicates the level of organ or tissue function.

(Video) Positron Emission Tomography (PET)

Why is PET performed?

In general, PET scans may be used to evaluate organs and/or tissues for the presence of disease or other conditions. PET may also be used to evaluate the function of organs, such as the heart or brain. The most common use of PET is in the detection of cancer and the evaluation of cancer treatment.

More specific reasons for PET scans include, but are not limited to, the following:

  • To diagnose dementias (conditions that involve deterioration of mental function), such as Alzheimer's disease, as well as other neurological conditions such as:

    (Video) How does a PET scan work?

    • Parkinson's disease. A progressive disease of the nervous system in which a fine tremor, muscle weakness, and a peculiar type of gait are seen.

    • Huntington's disease. A hereditary disease of the nervous system which causes increasing dementia, bizarre involuntary movements, and abnormal posture.

    • Epilepsy. A brain disorder involving recurrent seizures.

    • Cerebrovascular accident (stroke)

  • To locate the specific surgical site prior to surgical procedures of the brain

  • To evaluate the brain after trauma to detect hematoma (blood clot), bleeding, and/or perfusion (blood and oxygen flow) of the brain tissue

  • To detect the spread of cancer to other parts of the body from the original cancer site

  • To evaluate the effectiveness of cancer treatment

    (Video) Positron Emission Tomography | PET

  • To evaluate the perfusion (blood flow) to the myocardium (heart muscle) as an aid in determining the usefulness of a therapeutic procedure to improve blood flow to the myocardium

  • To further identify lung lesions or masses detected on chest X-ray and/or chest CT

  • To assist in the management and treatment of lung cancer by staging lesions and following the progress of lesions after treatment

  • To detect recurrence of tumors earlier than with other diagnostic modalities

How is PET performed?

PET scans can be done on an outpatient basis. It is also possible that some hospital inpatients may undergo a PET examination for certain conditions.

Although each facility may have specific protocols in place, generally, a PET scan procedure follows this process:

  1. The patient will be asked to remove any clothing, jewelry, or other objects that may interfere with the scan.

    (Video) Positron Emission Tomography (PET) Part 1

  2. If asked to remove clothing, the patient will be given a gown to wear.

  3. The patient will be asked to empty his or her bladder prior to the start of the procedure.

  4. One or 2 IV lines will be started in the hand or arm for injection of the radionuclide.

  5. Certain types of scans of the abdomen or pelvis may require that a urinary catheter be inserted into the bladder to drain urine during the procedure.

  6. In some cases, an initial scan may be performed prior to the injection of the radionuclide, depending on the type of study being done. The patient will be positioned on a padded table inside the scanner.

  7. The radionuclide will be injected into the IV. The radionuclide will be allowed to concentrate in the organ or tissue for about 30 to 60 minutes. The patient will remain in the facility during this time. The patient will not be hazardous to other people, as the radionuclide emits less radiation than a standard X-ray.

  8. After the radionuclide has been absorbed for the appropriate length of time, the scan will begin. The scanner will move slowly over the body part being studied.

  9. When the scan has been completed, the IV line will be removed. If a urinary catheter has been inserted, it will be removed.

    (Video) PET (Positron Emission Tomography) scan: What to expect

FAQs

What is positron emission tomography PET used for? ›

A positron emission tomography (PET) scan is an imaging test that can help reveal the metabolic or biochemical function of your tissues and organs. The PET scan uses a radioactive drug (tracer) to show both normal and abnormal metabolic activity.

What does a PET scan involve? ›

What is a PET scan? A PET scan uses a radiotracer to measure things like blood flow, oxygen use and sugar metabolism. A PET scan shows how your tissues and organs are functioning. It also can let you and your doctors know if cancer treatment is working.

What is the difference between CT and PET scan? ›

A CT scan shows detailed pictures of the organs and tissues inside your body. A PET scan can find abnormal activity and it can be more sensitive than other imaging tests. It may also show changes to your body sooner. Doctors use PET-CT scans to provide more information about the cancer.

What is the most common reason for a PET scan? ›

The most common use for a PET scan is for cancer, when it may be done: To see how far cancer has spread. This helps to select the best treatment approach. To check how well your cancer is responding, either during treatment or after treatment is completed.

Is it safe to be around pets after a PET scan? ›

With a PET or a PET/CT scan, you will give off very low levels of radiation for around 6 hours afterwards. As a precaution, you should avoid being close to women who are pregnant during this time. It should also be safe to be around adult pets, as long as they are not pregnant.

Does a PET scan show all cancers? ›

Not all cancers show up on a PET scan. PET scan results are often used with other imaging and lab test results. Other tests are often needed to find out whether an area that collected a lot of radioactive material is non-cancerous (benign) or cancerous (malignant).

How do they prepare you for a PET scan? ›

Before the PET-CT scan

You may need to remove anything that contains metal, such as eyeglasses, dentures, or hearing aids, during the test. An intravenous (IV) line will be placed into a vein. You will then receive an injection of a radioactive substance, called a radiotracer or tracer.

How does a person prepare for a PET scan? ›

Do not eat or drink anything, except water, for 6 hours before the exam. You may drink water, as much water as you can would be helpful, until arrival. Routine medications may be taken, unless you have been instructed otherwise.

Are you asleep during a PET scan? ›

After the injection, patients wait approximately one hour while the injected material is distributed throughout the body. Then, the patient will be asked to lie on a table that passes slowly through the scanner. The scanner resembles a CT scanner, but has a much larger opening. Some people fall asleep during the scan.

What cancers show up on a PET scan? ›

PET scans can show solid tumors in the brain, prostate, thyroid, lungs, and cervix. The scans can also evaluate the occurrence of colorectal, lymphoma, melanoma, and pancreatic tumors. They are also used to assess if treatment is being effective in eliminating cancer.

What is the biggest disadvantage in using a PET scan? ›

The major drawback to standard PET is that the images are of substantially lower resolution than, for example, those of CT and MRI, and PET is generally poor at delineating anatomic detail.

What are the side effects of PET scan? ›

PET Scan Risks and Side Effects
  • Pain or redness where a tracer is injected.
  • A hard time fitting into the PET/CT machine if you are overweight.
  • Claustrophobia, if you are unable to be in enclosed spaces.
  • Allergic reactions to a tracer, although this rarely happens and may be a mild reaction.
Jun 25, 2020

How long does it take to get the results of a PET scan? ›

When should I get my PET scan results? A radiologist with specialized training in PET scans will review the images, write a report and send it to your healthcare provider. This process usually takes 24 hours.

How painful is PET scan? ›

Depending on which part of the body the machine needs to scan, a PET scan should take about 30–60 minutes. The scan is not painful. If the person feels unwell, they can press a buzzer to alert the staff.

Why do doctors not do PET scans? ›

PET and PET-CT scans have risks.

Also, PET, and especially PET-CT scans, expose you to high levels of radiation. The effects of radiation add up over your lifetime. This can increase your risk of cancer. Multiple scans should not be done unless medical evidence shows that they would help.

How long do you have to stay away from a PET scan? ›

The radioactive tracer gives off very small levels of radiation that go away very quickly. As a precaution, you should avoid close contact with pregnant women, babies and young children for 6 hours after the scan. You need someone to take you home and stay overnight if you've had medicine to help you relax (sedative).

Why can't you be around kids after a PET scan? ›

As a precaution, you may be advised to avoid close contact with pregnant women, babies and young children for a few hours after having a PET scan. This is because you'll be slightly radioactive during this time.

Who should not have a PET scan? ›

Don't have a PET scan if you think you might be pregnant. Nursing Mothers. Additionally, nursing mothers should pump and store breast milk before the test; they will not be able to resume breastfeeding for 24 hours following the test.

Do you need a biopsy after a PET scan? ›

For nodules that are not metabolically active during the PET/CT scan, it's not recommended to follow up with a biopsy. So patients avoid the risks of an unnecessary procedure. However, if the nodule positively reacts to the radiotracer, further investigation and a biopsy are strongly recommended.

What cancers Cannot be detected by PET scan? ›

Though most cancers are picked up on PET CT, there are a few which do not. The most important of these would be cancer of stomach (signet cell type). In such cases performing this test would be waste. However, there are cancers which are very sensitively detected which include lymphoma, GIST, etc.

Can a PET scan tell if a tumor is cancerous? ›

PET imaging can be useful to determine whether a tumor is malignant (cancerous) or benign (not cancerous). Unlike other imaging tests like CT or MRI that show anatomy, the PET scan looks at the physiological changes and cellular activity, so cancer may be diagnosed much earlier.

Can you feel dizzy after PET scan? ›

What happens after a PET scan? Be sure to move slowly when getting up from the scanner table to avoid any dizziness or lightheadedness. You will be instructed to drink plenty of fluids and empty your bladder often for 24 to 48 hours after the test. This will help flush the remaining radioactive tracer from your body.

How do you stay calm during a PET scan? ›

Managing Anxiety Related to Scan Results
  1. Meditate — Practicing mindfulness or meditation can help you stay calm during difficult times. ...
  2. Exercise — Exercise not only benefits your health, but also improves your mood and reduces stress.
Jun 7, 2021

Do you wear clothes during a PET scan? ›

Specific protocols may vary, but generally a PET scan follows this process: You will be asked to remove any clothing, jewelry, or other objects that may interfere with the scan. If you are asked to remove clothing, you will be given a gown to wear.

Does a PET scan look at the whole body? ›

Scanning the whole body all at once

PET (positron emission tomography) is an extremely safe and powerful method for imaging inside the body, used to evaluate organs and other tissues for potential diseases, including cancer.

Can you pee before a PET scan? ›

If you're having a brain PET-CT, it is important to limit brain activity before your scan. Your nurse may tell you not to read or listen to music while you're waiting for your scan. Your care team will ask you to urinate (pee) just before your scan.

How long does it take to do a full body PET scan? ›

The entire PET scan process takes about two hours. It can take up to 60 minutes for your body to absorb the injected radiotracer. During this time, you'll need to sit quietly and limit your movements. The actual PET scan takes about 30 minutes.

What part of the body does a PET scan look at? ›

In general, PET scans may be used to evaluate organs and/or tissues for the presence of disease or other conditions. PET may also be used to evaluate the function of organs, such as the heart or brain. The most common use of PET is in the detection of cancer and the evaluation of cancer treatment.

Why do you have to rest before a PET scan? ›

You will need to wait at the facility for one to two hours so your body can absorb the tracer, and you should rest quietly during this period. Before the scan, you will have the opportunity to ask your technologist any questions you may have about the procedure.

How uncomfortable is a PET scan? ›

The scan is completely painless, but you may feel uncomfortable lying still for this long. If you feel unwell at any point there is a buzzer you can press to alert the medical team.

What are the side effects of a PET scan? ›

PET Scan Risks and Side Effects
  • Pain or redness where a tracer is injected.
  • A hard time fitting into the PET/CT machine if you are overweight.
  • Claustrophobia, if you are unable to be in enclosed spaces.
  • Allergic reactions to a tracer, although this rarely happens and may be a mild reaction.
Jun 25, 2020

Is A PET scan better than an MRI? ›

MRI scans, note that both can detect diseases and abnormalities. However, PET scans can show how your body performs at the cellular level. On the other hand, PET scans include radiation. MRI scans don't expose you to harmful radiation, which can be preferable for certain patients and annual scans.

How many PET scans can you have in your lifetime? ›

Medicare limits the number of PET scans following initial cancer treatment to three per patient. (More could be covered if deemed necessary by the doctor.) “These are good scans and appropriate in many situations,” Healy says.

How long do you stay away from people after a PET scan? ›

The radioactive tracer gives off very small levels of radiation that go away very quickly. As a precaution, you should avoid close contact with pregnant women, babies and young children for 6 hours after the scan. You need someone to take you home and stay overnight if you've had medicine to help you relax (sedative).

Can you brush your teeth before a PET scan? ›

Can I brush my teeth before a PET/CT scan? Normal brushing without swallowing mouthwash or toothpaste within the four hour preparation timeframe will have no effect on the outcome of your PET/CT scan.

Videos

1. What is PET/CT and how does it work?
(Siemens Healthineers)
2. How Does a PET Scan Work?
(NIBIB gov)
3. Introduction to Positron Emission Tomography (2019)
(MGH Martinos Center)
4. PET vs SPECT | Nuclear medicine
(Dr. Paulien Moyaert)
5. Principles of Positron Emission Tomography by Dr. Pankaj Tandon
(Nuclear Medicine Solutions)
6. KMH - Positron Emission Tomography / Computed Tomography (PET/CT)
(KMHCanada)
Top Articles
Latest Posts
Article information

Author: Allyn Kozey

Last Updated: 01/25/2023

Views: 5909

Rating: 4.2 / 5 (43 voted)

Reviews: 82% of readers found this page helpful

Author information

Name: Allyn Kozey

Birthday: 1993-12-21

Address: Suite 454 40343 Larson Union, Port Melia, TX 16164

Phone: +2456904400762

Job: Investor Administrator

Hobby: Sketching, Puzzles, Pet, Mountaineering, Skydiving, Dowsing, Sports

Introduction: My name is Allyn Kozey, I am a outstanding, colorful, adventurous, encouraging, zealous, tender, helpful person who loves writing and wants to share my knowledge and understanding with you.