PET studies have included measurements of glucose metabolism, cerebral blood flow, oxygen metabolism, dopamine, opiate, serotonin, and glutamate, as well as the imaging of various other physiological processes. Currently glucose metabolism is measured by [Fluorine-18] fluoro-2-deoxy-D-glucose (FDG), cerebral blood flow is measured by [Oxygen-15], oxygen metabolism is measured by [Oxygen-15]oxygen in combination with [Oxygen-15]water, and L-DOPA uptake and presumably dopamine metabolism is measured by [Fluorine-18] labeled DOPA.
Under normal conditions, the human brain depends on glucose as its only energy source. The majority of glucose is used for maintaining the membrane potentials and restoring ion gradients. [19] When clinically measuring glucose metabolism, the subject lies still for roughly 40 minutes after having FDG intravenously injected into their bloodstream. During this 40-minute time frame, the FDG is taken up by cells and will reach equilibrium. The distribution of the Fluorine-18 is then measured in multiple tomographic sections, and this distribution will be based on cerebral glucose utilization under the specific pathological or mental condition of the brain. One of the more vital uses for measuring glucose metabolism is because of the high glycolic rate of many malignancies. PET imaging has the ability to detect the presence of malignant tissues and to quantify changes in tumor glycolysis during and after treatment. [26]
The Cerebral Blood Flow (CBF) technique utilizes the physiological and pathological alterations in regional blood supply. It is assumed that increases in blood flow are associated with increased functional activity. In order to achieve activation, an activity lasting roughly 3-5 minutes is required. Upon achieving activation, the Oxygen-15 distribution can be measured and then through the use of the color-coded images of CBF it is possible to see where the brain is activated when partaking in certain activities. For example, when a person speaks or reads, the right hemisphere of the brain "lights up".