The positron emission tomography is an imaging technique based on the principle of scintigraphy. It belongs to the field of nuclear medicine.
They will inject a radioactive substance via vein which then accumaltest in your body during a short waiting time. The radiation then can be measured by a computer tomography.
Thus, the biochemical and physiological function of a particular organ can be determined. (With other imagine techniques like MRI or CT only the structure can be shown, but not the function)
In our case, the brain metabolism is measured and it can be detected whether there is a dysfunction because of a possible less blood circulation.
Because of the high radiation exposure it should be carefully considered whether this investigation is really necessary.