How is a tumor's metabolic activity assessed using PET?

• A. By measuring the size of the tumor
• B. By analyzing blood flow
• C. By measuring the uptake of radiotracers
• D. By observing physical changes in the tumor

Answer: (C)

The assessment of a tumor's metabolic activity using PET (Positron Emission Tomography) primarily involves measuring the uptake of radiotracers. In PET imaging, radiotracers, such as fluorodeoxyglucose (FDG), are injected into the body. These tracers are similar to glucose and are taken up by cells, particularly those that are metabolically active like cancer cells. The degree of uptake can provide critical insights into the tumor's level of metabolic activity. High uptake levels generally indicate heightened metabolic activity, which is often characteristic of malignant tumors.

This method is superior in evaluating the metabolic aspects of tumors compared to other approaches. For instance, measuring the tumor's size alone does not provide information about its biochemical behavior or activity level, which are crucial in oncology. Similarly, analyzing blood flow can contribute valuable information but does not specifically quantify the metabolic processes occurring within the tumor itself. Observing physical changes in the tumor may indicate growth or response to therapy, but again does not directly reflect the metabolic activity which is essential for assessing tumor aggressiveness or response to treatment. Thus, measuring the uptake of radiotracers is critical in diagnosing and monitoring cancer through the lens of metabolic functional imaging.