Drug treatment of AIDS dementia. Coloured positron emission tomography (PET) scans of axial sections through the human brain. The brain at left (1) is that of a normal control subject. The brain at centre (2) is that of an AIDS (acquired immune deficiency disorder) patient suffering dementia. At right (3) is the same patient 13 weeks after treatment with the anti-retroviral drug AZT (azidothymidine). The increase in red, yellow and green areas denotes a rise in glucose metabolism, indicating an improvement in brain function. PET scans use gamma cameras to detect radioactive tracers that have been injected into the blood, and which accumulate in areas of high metabolic activity.