Positron Emission Tomography (PET Scan)

A PET scan is a type of imaging test that uses a radioactive tracer to visualize and measure the metabolic activity of cells in the body. It is commonly used to diagnose and monitor various medical conditions, including cancer, neurological disorders, and cardiovascular disease.

How it Works

A PET scan works by injecting a small amount of a radioactive tracer into the bloodstream. The tracer is typically a glucose molecule that has been tagged with a positron-emitting radionuclide, such as fluorine-18 (F-18). The tracer accumulates in areas of high metabolic activity, such as cancer cells or inflamed tissues.

As the positrons emitted by the tracer interact with electrons in the surrounding tissue, they produce gamma rays. These gamma rays are detected by a special camera called a PET scanner, which is designed to detect and record the gamma rays emitted by the tracer.

Types of PET Scans

There are several types of PET scans, including:

• F-18 FDG PET scan: This is the most common type of PET scan, which uses F-18 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.
• N-13 ammonia PET scan: This type of PET scan uses N-13 ammonia as the tracer and is used to evaluate cardiovascular disease, including coronary artery disease and cardiac sarcoidosis.
• O-15 water PET scan: This type of PET scan uses O-15 water as the tracer and is used to evaluate cerebral blood flow and perfusion.
• Rb-82 PET scan: This type of PET scan uses Rb-82 as the tracer and is used to evaluate myocardial perfusion and coronary artery disease.

Indications for PET Scans

PET scans are commonly used to:

• Diagnose cancer: PET scans can help diagnose various types of cancer, including lung, breast, colon, and lymphoma.
• Monitor cancer treatment: PET scans can be used to evaluate the effectiveness of cancer treatment and detect any recurrence of cancer.
• Evaluate neurological disorders: PET scans can help diagnose and monitor neurological disorders such as Alzheimer's disease, Parkinson's disease, and epilepsy.
• Evaluate cardiovascular disease: PET scans can be used to evaluate coronary artery disease, cardiac sarcoidosis, and other cardiovascular conditions.

Benefits of PET Scans

PET scans have several benefits, including:

• High sensitivity and specificity: PET scans can detect small changes in metabolic activity, making them highly sensitive and specific for diagnosing various medical conditions.
• Non-invasive: PET scans are non-invasive and do not require any surgical incisions or insertion of instruments into the body.
• Low radiation exposure: The amount of radiation exposure from a PET scan is relatively low, especially when compared to other imaging tests such as CT scans.

Risks and Side Effects

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

• Radiation exposure: While the amount of radiation exposure from a PET scan is relatively low, it can still pose a risk to pregnant women and young children.
• Allergic reactions: Some people may experience an allergic reaction to the tracer used in the PET scan.
• Claustrophobia: The PET scanner can be confining, which may cause anxiety or claustrophobia in some individuals.

Preparation for a PET Scan

To prepare for a PET scan:

• Fast for at least 4-6 hours: Fasting can help ensure that the tracer is distributed evenly throughout the body.
• Avoid strenuous exercise: Avoiding strenuous exercise for 24 hours before the scan can help reduce muscle activity and improve image quality.
• Remove metal objects: Remove any metal objects, such as jewelry or glasses, that may interfere with the scan.

What to Expect During a PET Scan

During a PET scan:

• The tracer will be injected into a vein in your arm: The tracer is typically injected about 30-60 minutes before the scan.
• You will lie on a table and be positioned inside the PET scanner: The PET scanner is a large, doughnut-shaped machine that takes pictures of your body.
• The scan will take about 15-90 minutes to complete: The length of the scan depends on the type of tracer used and the area of the body being imaged.