The availability of PET has shed a new, exciting light onto many brain diseases and pathological conditions. For example, the image at the right shows the abnormally high activation of the right part of the brain of a patient during an epileptic seizure (the yellow and magenta patches). What you see here is a series of transversal sections, i.e, the apparatus gets images like horizontal slices through the brain. Each slice is made at a different level, a few centimeters from the preceding one. This allows the physician to locate with remarkable precision where the changes induced by the disease are taking place. This information can be used to understand better what is going on, to make a better diagnosis, or even to allow a surgical intervention, if necessary.