Positron Emission Tomography (PET) Scans

Positron emission tomography (PET) scans are a type of medical imaging test that uses a radioactive tracer to visualize and measure the metabolic activity of cells in the body.

How PET Scans Work

PET scans work by injecting a small amount of a radioactive tracer, typically a sugar molecule or amino acid, into the bloodstream. The tracer is absorbed by cells in the body, with higher concentrations accumulating in areas of high metabolic activity, such as cancer cells.

The tracer emits positrons, which are positively charged particles that collide with electrons in the surrounding tissue, producing gamma rays. These gamma rays are detected by a PET scanner, which uses specialized detectors to capture and record the signals.

Types of PET Scans

• F-18 FDG PET scan: This is the most common type of PET scan, using fluorodeoxyglucose (FDG) as the tracer. It is used to diagnose and monitor cancer, as well as to evaluate neurological disorders such as Alzheimer's disease.
• Nitrogen-13 ammonia PET scan: This type of scan uses nitrogen-13 ammonia as the tracer and is used to evaluate cardiovascular disease, including coronary artery disease.
• Oxygen-15 water PET scan: This type of scan uses oxygen-15 water as the tracer and is used to evaluate cerebral blood flow and metabolism.

Uses of PET Scans

PET scans are used to diagnose and monitor a variety of conditions, including:

• Cancer: to detect and stage cancer, as well as to monitor response to treatment
• Neurological disorders: such as Alzheimer's disease, Parkinson's disease, and epilepsy
• Cardiovascular disease: to evaluate coronary artery disease and cardiac function
• Infectious diseases: such as tuberculosis and pneumonia

Risks and Side Effects

PET scans are generally safe, but there are some potential risks and side effects to consider:

• Radiation exposure: PET scans involve exposure to small amounts of radiation, which can increase the risk of cancer over time.
• Allergic reactions: some people may be allergic to the tracer used in the scan.
• Claustrophobia: some people may experience anxiety or discomfort during the scan due to the enclosed space of the scanner.

Preparation and Procedure

To prepare for a PET scan, patients are typically asked to:

• Fast for several hours before the scan
• Avoid strenuous exercise and caffeine
• Remove any metal objects or jewelry

The procedure itself typically involves:

• Injection of the tracer into a vein in the arm
• A waiting period of 30-60 minutes to allow the tracer to accumulate in the body
• Lying on a table that slides into the PET scanner
• The scan itself, which can take anywhere from 15-60 minutes