Coloured computed tomography (CT) and positron emission tomography (PET) composite scan (left) and coloured CT scan (right) of the axial section through a normal human brain. CT scans provide detailed images of the body?™s internal structures, such as bones, organs and tissues. PET scanning using radioisotopes shows variation in metabolic activity in the bodys internal organs which is often indicative of cancerous cells because they consume more glucose than normal cells.