Molecular imaging using positron emission tomography (PET) is able to show how brains are altered by addictive drugs. Researchers from the Center for Translational Neuroimaging at the U.S. Department of Energy’s Brookhaven National Laboratory are pioneering radioactively “tagged” molecules for use in PET studies. The radiotracers (compounds labeled with a radioactive form of certain chemical elements such as carbon or fluorine) being studied are injected into a research subject’s bloodstream. A PET scanner picks up the radioactive signal from the tracer and continuously tracks its concentration and movement through the body. The data can be used to reconstruct 3D images that reveal where the compound goes in the body/brain and how long it stays. For the research, radiotracers have been developed to track the movement of various addictive drugs including cocaine, nicotine, and methamphetamine and also to measure the levels of certain “chemical messengers,” or neurotransmitters, and their receptors in the brain. These studies have shown the brain’s ability to respond to pleasure signals becomes depleted as receptors for dopamine are lost. The research has also indicated that initial differences in people’s dopamine systems may help explain why some people find drugs pleasurable and become addicted while others do not and could provide a better understanding of how to cope with a treat addition.