PET (Positron Emission Tomography) is a state-of-the-art nuclear medicine technique for evaluating biochemical and physiological processes in the body. In the early stages of most diseases, such functional processes are altered. First, PET detects these changes, often before anatomical or structural changes are evident on MRI or CT scan. In short, PET is a functional imaging modality, as compared to CT scan, which is a structural imaging modality.