PET scans show chemical activity levels in the body, which help identify brain disorders such as Alzheimer's disease, heart disease and certain cancers, according to Mayo Clinic. As of 2015, positron emission tomography scans reveal cancers in the breast, cervix, lung, prostate, pancreas and other parts of the body.
Since cancerous cells have a higher metabolic rate than normal cells, the malignant cells appear as bright spots on PET scans. The scans help detect cancer and whether it is spreading, reoccurring or in remission. However, many cancers do not appear on PET scans, notes Mayo Clinic. PET scans also reveal reduced heart blood flow; the data can assist a doctor in determining when to recommend angioplasty or heart bypass surgery.