A: PET stands for Positron Emission Tomography. It is an imaging technique that uses small quantities of radioactive tracers to produce images. PET scanning has now been developed to facilitate the early diagnosis of Alzheimer's disease and shows if there is deposition of amyloid protein in the brain. CT (Computed Tomography) utilises X-rays to produce pictures showing the density of the brain. By combining these two techniques in one scanner important information about the brain in obtained.