A Positron Emission Tomography (PET) scan is a medical imaging technique that provides a functional view of the body’s tissues and organs. Unlike X-rays or CT scans, it shows metabolic activity rather than just anatomical structures. This helps in detecting, diagnosing, and monitoring various diseases, particularly cancer.
Understanding the PET Scan Process
A PET scan uses a radioactive tracer, typically fluorodeoxyglucose (FDG), a sugar molecule. This tracer is injected into a vein and travels throughout the body. Cancer cells have a high metabolic rate and increased glucose consumption, so they absorb more FDG than healthy cells.
After the tracer is absorbed, a PET scanner detects the emitted radiation. This creates detailed images that highlight areas of elevated metabolic activity. The scanner maps where the sugar is used most actively, providing functional information about the body’s processes.
Identifying Cancer on a PET Scan
On a PET scan, cancer typically appears as “hot spots,” which are areas of increased brightness or intense color. While specific colors (e.g., red, orange, yellow) depend on the chosen scale, intensity signifies higher metabolic activity. These bright spots indicate cells are consuming the radioactive sugar tracer at an abnormally high rate.
This elevated metabolic activity is a hallmark of many cancerous tumors, which often grow and divide rapidly, requiring more energy. The size and intensity of these hot spots can offer clues about a tumor’s activity or potential aggressiveness. Conversely, the absence of hot spots where cancer was suspected can be a significant finding, suggesting a lack of active disease.
Other Conditions That Appear on a PET Scan
Not every “hot spot” on a PET scan indicates cancer. Other conditions can also lead to increased metabolic activity and appear as bright areas, sometimes called false positives. For instance, inflammation from infections, arthritis, or recent surgery can cause cells to become highly active and absorb more FDG.
Benign tumors, which are non-cancerous growths, may also show increased metabolic activity. Furthermore, normal physiological processes, such as muscle activity, brain activity, or the presence of brown fat, naturally consume glucose, appearing as hot spots. Therefore, a PET scan alone is not always definitive for a cancer diagnosis and often requires further evaluation.
Interpreting PET Scan Findings
PET scan results are integrated into a patient’s overall medical picture. These scans are valuable for several aspects of cancer care, including determining if cancer has spread (staging). They also monitor treatment effectiveness, such as chemotherapy or radiation, by observing changes in tumor metabolic activity.
PET scans can also help detect if cancer has returned after treatment. They can guide biopsies by pinpointing suspicious areas for further investigation. A specialized physician, such as a nuclear medicine physician or radiologist, interprets the images in conjunction with a patient’s medical history, physical examination, and other imaging studies like CT or MRI.