Positron Emission Tomography (PET) scans provide functional information about tissues and organs. Unlike imaging methods that display anatomical structures, PET scans reveal metabolic activity, offering insights into how cells are functioning.
Understanding How PET Scans Work
A PET scan introduces a small amount of a radioactive tracer, often fluorodeoxyglucose (FDG), intravenously. The radiotracer travels through the bloodstream and accumulates in metabolically active cells. Cells with higher metabolic rates, such as cancer cells, tend to absorb more of this tracer.
The PET scanner detects energy emitted as the radiotracer decays. When radioactive atoms release positrons, they collide with electrons, producing gamma rays. The scanner captures these gamma rays, and a computer constructs detailed three-dimensional images that map the tracer’s distribution and metabolic activity.
Decoding What You See in PET Images
PET scan images display colors or intensities representing varying levels of metabolic activity. Brighter, “hotter” areas, often in colors like red or orange, indicate higher radiotracer concentrations and increased metabolic activity. Conversely, darker, “cooler” areas, often in shades of blue, green, or black, suggest minimal radiotracer uptake and lower metabolic activity.
Increased activity, appearing as brighter spots, can suggest several conditions. Rapidly growing cancer cells often exhibit high metabolic rates and absorb more FDG. Inflammation or infection can also cause increased metabolic activity. Tissue healing following injury or surgery might show elevated tracer uptake.
Decreased activity, represented by darker regions, can indicate reduced cellular function, tissue damage, or necrosis. For example, in conditions like Alzheimer’s disease, brain areas may show reduced glucose metabolism. Context is important; a “hot spot” does not automatically mean disease, and a “cold spot” does not always mean health.
Common Applications of PET Scans
In oncology, PET scans are used for detecting cancer, staging its spread, and monitoring treatment effectiveness. They identify metabolically active cancer cells, often before structural changes are visible on other imaging tests. They also help assess recurrence.
In neurology, PET scans evaluate brain disorders by assessing activity and metabolism. They are used in the diagnosis and management of conditions like Alzheimer’s disease, by showing patterns of glucose metabolism, and epilepsy, by identifying abnormal brain activity. They can also differentiate neurodegenerative conditions.
Cardiology uses PET imaging to assess heart function and blood flow. PET scans determine heart attack effects, identify areas with insufficient blood flow, and assess myocardial viability (distinguishing damaged from salvageable tissue). This information guides treatment decisions for heart conditions.
Factors Influencing Image Interpretation
Patient preparation, including fasting and managing blood sugar, is important. High blood glucose affects radiotracer absorption, potentially leading to less clear or inaccurate results. Patients with diabetes receive specific instructions for optimal scan quality.
Benign conditions can also show increased radiotracer uptake, mimicking disease. Inflammation, infection, or muscle contractions can lead to increased metabolic activity. This highlights the need for thorough medical evaluation beyond scan images.
PET scans are often combined with Computed Tomography (CT) or Magnetic Resonance Imaging (MRI) to create hybrid images (PET/CT or PET/MRI). This combination provides both functional and anatomical information, helping precisely locate metabolic activity within body structures. A trained radiologist or nuclear medicine physician interprets PET scan images, integrating findings with a patient’s medical history and other diagnostic tests for an accurate diagnosis.