A good example of the fantastic imaging capabilities of PET is shown in the images at the left, made by Dr. Marcus Raichle, at the Neuroimaging Lab or the Washington University School of Medicine, St Louis, USA.
They were taken under two different conditions. In the first one (uppermost image), an individual was hearing a text, in order to learn a new language task. The color map shows the regions of the brain which were activated by this task, in other words, where there were cells working more than in their resting state, with a higher metabolism (using more energy and more blood flow). The PET machine shows the degree of activity in several tones of color, like in a rainbow. Yellow and red regions are "hotter", that is, they indicate a higher cell activity. Blue and black regions show decreased activity or none at all. While obtaining this image, the patient was still unpracticed at the language learning task. The highest brain activities are shown in an area called temporal lobe, responsible for the hearing perception, and in another area called prefrontal cortex, responsible for understanding language.