A PET scan (Positron Emission Tomography) is a medical imaging test used to observe the metabolic or biochemical function of organs and tissues in the body. It is primarily used for:

• Detecting and monitoring cancers, as it can show where cancer is located, its size, and whether it has spread.
• Differentiating between active tumors and scar tissue.
• Assessing neurological diseases like Alzheimer's, Parkinson's, and epilepsy by showing how different areas of the brain are functioning.
• Evaluating cardiovascular conditions by assessing blood flow to the heart and detecting damaged heart tissue.
• Helping doctors decide on the best treatment for cancer and monitoring how well the treatment is working.

The scan involves injecting a small amount of radioactive tracer, which accumulates in areas of higher metabolic activity, such as cancer cells, making these areas appear "brighter" on the scan images. PET scans are often combined with CT or MRI scans to provide more detailed structural and functional information. Thus, a PET scan is mainly used to detect cancer, neurological diseases, and heart-related conditions by showing how tissues and organs are functioning in real time rather than just their structure.