Table of ContentsView AllTable of ContentsPurposeProcedureSide EffectsRisks and ContraindicationsResults
Table of ContentsView All
View All
Table of Contents
Purpose
Procedure
Side Effects
Risks and Contraindications
Results
A positron emission tomography (PET) scan provides detailed three-dimensional images of your internal body organs and tissue, which helps diagnose a wide range of conditions.
Some people worry about the side effects of a PET scan because a short-acting radioactive substance is injected into your body to produce the images. However, there are very few risks associated with a PET scan.
This article describes what PET scans are used for, including the diseases they can help diagnose, and how the procedure is performed. It also explains the possible risks and what the PET test results mean.
Purpose of a PET Scan
Positron emission tomography (PET) is an imaging test that detects changes in metabolism and your body’s biochemistry. The patterns of these changes can help diagnose different diseases.
PET scans use various radioactive drugs called radiotracers that are injected into your bloodstream. Tracers may be labeled forms of sugar, amino acids, ammonia, water, or other substances.\
Based on atypical changes, a PET scan can sometimes detect disease before other imaging tests, includingcomputed tomography (CT)ormagnetic resonance imaging (MRI).
PET is primarily used for the following purposes:
Cancer
Those that can include:
Cardiovascular Disease
Cardiovascular conditions PET can diagnose include:
Neurological Disorders
A PET scan can measure brain activity in relation to areas of high and low radioactivity. Since the brain requires large amounts of glucose and oxygen to function, any shortages can easily be detected on a scan.
Neurologic disorders a PET can help diagnose include:
Other ApplicationsIn addition, PET can detect bacterial infections, most specifically enterobacterial types associated withendocarditis,septic arthritis, andosteomyelitis.
Other Applications
In addition, PET can detect bacterial infections, most specifically enterobacterial types associated withendocarditis,septic arthritis, andosteomyelitis.
Combination Scanning
When diagnosing a disease, there is an advantage to looking at both the cause and consequence of a disease. For this reason, a PET is frequently combined with CT or MRI to provide the healthcare provider with both anatomical (physical) and metabolic (biochemical) information.
Modern PET scanners are now available with integrated CT scanners (PET-CT) or MRI scanners (PET-MRI), which create two sets of precisely matched images.
How PET Scans Are Done
Prepare for the Scan
In preparation for the scan, you will need to eat a low-carbohydrate, no-sugar diet 24 hours beforehand to keep your blood sugar within normal limits. As a general rule, you would avoidhigh glycemic index (GI) foodslike bread, dairy, pasta, and juices that raise your blood sugar.
You need to avoid strenuous exercise 24 hours before the test, which can alter your normalinsulin responseand cause a drop in your blood sugar (hypoglycemia).
Six hours before the scan, you will need to stop eating altogether. Four hours beforehand, insulin or any other diabetes medications would also need to be stopped.
PET Scan Procedure
The PET scanner is a large machine with a doughnut-shaped hole in the center, similar to a CT or MRI unit. The procedure itself is relatively standard and performed as follows:
The PET scan can take anywhere from 20 to 45 minutes to complete, depending on the purpose and scope of the test. Some variations of the test can take longer, particularly if a PET-CT or PET-MRI is performed.
Side Effects of PET Scan
The side effects of PET scans are relatively minor and mainly involve pain and swelling at the injection site.
Allergic reactions to the injection are rare, but let your healthcare provider know immediately if you experience symptoms like nausea, nasal congestion, hives, restlessness, or dizziness.
A PET scan is painless and poses few risks. The scanner itself does not emit radiation, and the amount of radiotracer used for the imaging is so small as to not require the use of standard radiation precautions.
Claustrophobia may be a concern for some patients. If being placed inside the tube-like device makes you nervous, let your healthcare provider know. If needed, you may be given a mild sedative such as low-dose Valium (diazepam) or Ativan (lorazepam).
Obesity
A PET scan may not be possible if you are obese and unable to fit into the scanning chamber. Most scanning tables have a maximum weight capacity of 450 pounds and a chamber diameter of only 27.5 inches (70 centimeters). Image quality may be degraded if weight and size limits are exceeded.
Moreover, the radiotracer dose may not be adequate to achieve a quality image if you are extremely overweight. While upping the dose may help, it cannot be raised beyond a certain point due to potential harm.
Newer multidetector scanners can overcome some of these concerns. A few manufacturers are also offering units with chambers as large as 30.5 inches (78 centimeters).
Pregnancy
On the other hand, a PET-CT scan may not be appropriate if you are pregnant. In general, CT scans are not recommended in people with pregnancy unless the benefits clearly outweigh the potential risks.
Always let your healthcare provider know if you are pregnant or nursing before a PET scan.
Diabetes
You can have a PET scan if you have diabetes but need to ensure that yourblood glucose levelsare under 200 mg/dL before scanning. If your glucose levels are high, the radiotracer will not be taken up efficiently in cells.
On the other hand, if your insulin is high, it will cause an increased uptake of the radiotracer and throw off the results.
If your blood sugar is uncontrolled, you need to advise your healthcare provider in advance so that special dietary or pharmaceutical measures can be taken to achieve control.
Results of a PET Scan
The PET images will usually be sent to your healthcare provider within 48 hours, along with a report detailing the normal and abnormal findings.
By contrast, areas with less radiotracer uptake are known as “cold spots.” This indicates areas of low metabolic activity, often the result of reduced blood flow or possiblytissue necrosis(tissue death).
Summary
PET scans can be used to detect different types of cancers, cardiovascular diseases, and neurological disorders. Side effects are few, and there are no absolute contraindications to the scan other than obesity due to the size and weight limitations of the units.
6 SourcesVerywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read oureditorial processto learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.International Atomic Energy Agency.Standard Operating Procedures for PET/CT: A Practical Approach for Use in Adult Oncology.University of California, San Francisco.PET/CT Scan: How to prepare, what to expect, and safety tips.International Atomic Radiation Agency.Radiation protection of patients during PET/CT scanning.Grilo A, Vieira L, Carolino E, et al.Anxiety in Cancer Patients during F-FDG PET/CT Low Dose: A Comparison of Anxiety Levels before and after Imaging Studies. Nurs Res Pract. 2017;2017:3057495. doi:10.1155/2017/3057495Toshimitsu S, Fujino K, Hirokawa Y.Effects of the Obesity Type on FDG-PET Image Quality. Nihon Hoshasen Gijutsu Gakkai Zasshi. 2017;73(8):672-679. doi:10.6009/jjrt.2017_JSRT_73.8.672Burton SC, Frey K, Fahey F, et al.Fetal dose from PET and CT in pregnant patients.J Nuclear Med.2023;64(2):312-319. doi:10.2967/jnumed.122.263959
6 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read oureditorial processto learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.International Atomic Energy Agency.Standard Operating Procedures for PET/CT: A Practical Approach for Use in Adult Oncology.University of California, San Francisco.PET/CT Scan: How to prepare, what to expect, and safety tips.International Atomic Radiation Agency.Radiation protection of patients during PET/CT scanning.Grilo A, Vieira L, Carolino E, et al.Anxiety in Cancer Patients during F-FDG PET/CT Low Dose: A Comparison of Anxiety Levels before and after Imaging Studies. Nurs Res Pract. 2017;2017:3057495. doi:10.1155/2017/3057495Toshimitsu S, Fujino K, Hirokawa Y.Effects of the Obesity Type on FDG-PET Image Quality. Nihon Hoshasen Gijutsu Gakkai Zasshi. 2017;73(8):672-679. doi:10.6009/jjrt.2017_JSRT_73.8.672Burton SC, Frey K, Fahey F, et al.Fetal dose from PET and CT in pregnant patients.J Nuclear Med.2023;64(2):312-319. doi:10.2967/jnumed.122.263959
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read oureditorial processto learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
International Atomic Energy Agency.Standard Operating Procedures for PET/CT: A Practical Approach for Use in Adult Oncology.University of California, San Francisco.PET/CT Scan: How to prepare, what to expect, and safety tips.International Atomic Radiation Agency.Radiation protection of patients during PET/CT scanning.Grilo A, Vieira L, Carolino E, et al.Anxiety in Cancer Patients during F-FDG PET/CT Low Dose: A Comparison of Anxiety Levels before and after Imaging Studies. Nurs Res Pract. 2017;2017:3057495. doi:10.1155/2017/3057495Toshimitsu S, Fujino K, Hirokawa Y.Effects of the Obesity Type on FDG-PET Image Quality. Nihon Hoshasen Gijutsu Gakkai Zasshi. 2017;73(8):672-679. doi:10.6009/jjrt.2017_JSRT_73.8.672Burton SC, Frey K, Fahey F, et al.Fetal dose from PET and CT in pregnant patients.J Nuclear Med.2023;64(2):312-319. doi:10.2967/jnumed.122.263959
International Atomic Energy Agency.Standard Operating Procedures for PET/CT: A Practical Approach for Use in Adult Oncology.
University of California, San Francisco.PET/CT Scan: How to prepare, what to expect, and safety tips.
International Atomic Radiation Agency.Radiation protection of patients during PET/CT scanning.
Grilo A, Vieira L, Carolino E, et al.Anxiety in Cancer Patients during F-FDG PET/CT Low Dose: A Comparison of Anxiety Levels before and after Imaging Studies. Nurs Res Pract. 2017;2017:3057495. doi:10.1155/2017/3057495
Toshimitsu S, Fujino K, Hirokawa Y.Effects of the Obesity Type on FDG-PET Image Quality. Nihon Hoshasen Gijutsu Gakkai Zasshi. 2017;73(8):672-679. doi:10.6009/jjrt.2017_JSRT_73.8.672
Burton SC, Frey K, Fahey F, et al.Fetal dose from PET and CT in pregnant patients.J Nuclear Med.2023;64(2):312-319. doi:10.2967/jnumed.122.263959
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