Describe a common use for a PET scan.

A PET scan, or positron emission tomography scan, is primarily used to assess metabolic activity in tissues, which is particularly useful in cancer diagnosis. Unlike other imaging techniques that primarily focus on the anatomical structure, PET scans provide functional imaging. They detect gamma rays emitted from radioactive tracers that are introduced into the body, usually through an injection. These tracers are taken up by cells in proportion to their metabolic activity.

Cancer cells typically have a higher metabolic rate than normal cells, which allows PET scans to identify areas of increased activity indicative of tumors. This capability makes PET scans an invaluable tool in oncology for not only diagnosing cancer but also in evaluating treatment response, determining the extent of disease, and monitoring for recurrence.

Other methods listed, such as assessing bone density and finding fractures, are more aligned with X-rays or bone scans rather than PET scans, which focus on metabolic rather than structural assessment. Similarly, while soft tissue injuries can be visualized with techniques such as MRI and ultrasound, they are not the primary purpose of PET imaging. Thus, the use of PET scans in assessing metabolic activity is a well-established and crucial application, particularly in the context of cancer evaluation and management.