Positron emission tomography (PET) scans are powerful medical imaging tests that provide detailed pictures of the metabolic activity within your body. Unlike other imaging tests that primarily show the structure of organs and tissues, a PET scan reveals how these areas are functioning at a cellular level. This is achieved through the use of a radioactive tracer, allowing doctors to detect diseases, often before they become visible on CT scans or MRIs.
During a PET scan, you will lie on a comfortable table that gently slides into a PET scanner, a machine that resembles a large doughnut. The scan itself is typically painless and takes around 30 minutes to capture images of metabolic activity in your organs and tissues.
Why is a PET Scan Performed?
PET scans are valuable tools for diagnosing, monitoring, and managing a wide range of medical conditions. Healthcare providers use PET scans to gain critical insights into various diseases, including:
Detecting and Managing Cancer
Cancer cells are characterized by their rapid and uncontrolled growth, leading to a higher metabolic rate compared to normal cells. PET scans exploit this difference, as cancer cells appear as bright spots due to increased tracer uptake. In oncology, PET scans are instrumental for:
- Cancer Detection: Identifying cancerous tumors, sometimes even before they are detectable by other imaging methods.
- Staging Cancer: Determining if cancer has spread to other parts of the body (metastasis).
- Monitoring Treatment Effectiveness: Assessing how well cancer treatments, such as chemotherapy or radiation therapy, are working. A decrease in tracer uptake can indicate successful treatment.
- Detecting Cancer Recurrence: Identifying if cancer has returned after treatment.
PET scans, particularly when combined with CT or MRI (PET-CT or PET-MRI), are effective in visualizing various types of solid tumors, including cancers of the:
- Brain
- Breast
- Cervix
- Colorectal area
- Esophagus
- Head and Neck
- Lung
- Lymphatic System (Lymphoma)
- Pancreas
- Prostate
- Skin (Melanoma)
- Thyroid
It’s important to note that while PET scans are highly sensitive, some non-cancerous conditions can also exhibit increased metabolic activity and appear similar to cancer on a PET scan. Furthermore, not all types of cancer are detectable by PET scans. The interpretation of PET scan results requires expertise and careful consideration of other clinical factors.
Evaluating Heart Disease
PET scans play a significant role in assessing heart health by revealing areas of reduced blood flow to the heart muscle. This is crucial in determining the extent of damage from heart disease and in planning appropriate interventions. Specifically, PET scans can help determine if patients with coronary artery disease would benefit from:
- Coronary Artery Bypass Surgery: To reroute blood flow around blocked arteries.
- Angioplasty: A procedure to open up clogged arteries.
By visualizing blood flow and metabolic activity in the heart, PET scans assist healthcare providers in making informed decisions about the best course of treatment for heart conditions.
Investigating Brain Disorders
PET scans are also used to evaluate various brain disorders by examining metabolic activity in different brain regions. They can be helpful in diagnosing and monitoring conditions such as:
- Brain Tumors: Identifying and assessing the metabolic activity of brain tumors.
- Alzheimer’s Disease: Detecting patterns of decreased metabolic activity characteristic of Alzheimer’s, aiding in early diagnosis and differentiation from other forms of dementia.
- Seizure Disorders (Epilepsy): Identifying areas of abnormal brain metabolism that may be causing seizures.
PET scans provide valuable functional information about the brain that complements structural imaging techniques like MRI and CT, leading to a more comprehensive understanding of brain disorders.
Understanding the Risks of a PET Scan
A PET scan involves the injection of a small amount of radioactive tracer. While radiation exposure is a concern, the dose used in PET scans is minimal, and the risk of long-term negative effects is very low. However, it’s important to be aware of potential risks:
- Radiation Exposure to Unborn Babies: Pregnant women should inform their healthcare provider as the tracer could expose the fetus to radiation. PET scans are generally avoided during pregnancy unless absolutely necessary.
- Radiation Exposure to Breastfeeding Infants: Breastfeeding mothers should also inform their provider as the tracer can be excreted in breast milk and expose the infant to radiation. Temporary interruption of breastfeeding may be advised.
- Allergic Reactions: Although rare, allergic reactions to the tracer are possible. Inform your healthcare provider of any known allergies.
It is crucial to discuss any concerns and potential risks with your healthcare provider to weigh them against the benefits of the PET scan in your specific situation.
Preparing for Your PET Scan
Proper preparation is essential for obtaining accurate PET scan results. Your healthcare provider will give you detailed instructions tailored to your individual needs. General guidelines include:
- Inform Your Doctor: Disclose any allergies, recent illnesses, medical conditions (especially diabetes), medications (including vitamins and herbal supplements), pregnancy or breastfeeding status, and claustrophobia.
- Avoid Strenuous Exercise: Refrain from intense physical activity for a couple of days before the scan, as it can affect tracer distribution.
- Fasting: Typically, you will need to stop eating for at least four hours before the scan to ensure optimal tracer uptake.
- Hydration: Drinking plenty of water in the hours leading up to the scan can help with tracer excretion after the procedure.
Following these instructions carefully will contribute to the success and accuracy of your PET scan.
What to Expect During the PET Scan Procedure
The PET scan procedure is generally straightforward and well-tolerated. Here’s what you can expect:
- Arrival and Preparation: Upon arrival, you may be asked to change into a hospital gown and empty your bladder.
- Tracer Injection: A healthcare professional will inject the radioactive tracer into a vein in your arm or hand. You might feel a brief cold sensation.
- Waiting Period: You will rest quietly in a reclining chair for 30 to 60 minutes. This allows the tracer to circulate and be absorbed by your body’s tissues.
- Scanning Process: You will lie down on a narrow table that slides into the PET scanner. It’s crucial to remain still during the scan to prevent blurred images. The scan itself takes about 30 minutes for a PET-CT and 45 minutes for a PET-MRI. The machine may produce buzzing and clicking sounds.
- Managing Anxiety: If you experience claustrophobia or anxiety about enclosed spaces, inform the staff. Medication to help you relax can be provided.
The PET scan is painless, and the staff will ensure your comfort throughout the procedure.
After Your PET Scan
Following the PET scan, you can usually resume your normal daily activities unless instructed otherwise by your healthcare provider. It is recommended to:
- Drink Plenty of Fluids: This helps flush the radioactive tracer out of your body more quickly.
The small amount of remaining radioactivity in your body will naturally decay and be eliminated within a short period.
Understanding Your PET Scan Results
A radiologist, a doctor specializing in interpreting medical images, will analyze your PET scan images and send a report to your healthcare provider. The radiologist may compare your PET scan with other imaging tests, such as CT or MRI, to gain a comprehensive understanding of your condition. The combined information from PET and other imaging modalities often provides a more detailed and accurate diagnosis.
Clinical Trials and PET Scans
Explore Mayo Clinic studies are continuously being conducted to further refine and expand the applications of PET scan technology in preventing, detecting, treating, and managing various diseases. Participation in clinical trials can offer access to cutting-edge diagnostic and treatment approaches.
Positron emission tomography scan care at Mayo Clinic
Sept. 10, 2024
References:
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- What is PET? Society of Nuclear Medicine and Molecular Imaging. https://www.snmmi.org/AboutSNMMI/Content.aspx?ItemNumber=5649. Accessed April 6, 2021.
- Umterrainer M, et al. Recent advances of PET imaging in clinical radiation oncology. Radiation Oncology. 2020; doi:10.1186/s13014-020-01519-1.
- Adam A, et al., eds. Adrenal imaging. In: Grainger and Allison’s Diagnostic Radiology. 7th ed. Elsevier; 2021. https://www.clinicalkey.com. Accessed April 6, 2021.
- ACR-SPR practice parameters for performing FDG-PET/CT in oncology. American College of Radiology. https://www.acr.org/Clinical-Resources/Practice-Parameters-and-Technical-Standards/Practice-Parameters-by-Modality. Accessed April 6, 2021.
- Cervical cancer. Radiological Society of North America. https://www.radiologyinfo.org/en/info.cfm?pg=cervicalcancer. Accessed April 8, 2021.
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- Collins DA (expert opinion). Mayo Clinic. April 24, 2021.
