imaging armamentarium and, increasingly, of the therapeutic armamentarium as well, in the neurointerventional management of cerebral aneurysms and other blood-vessel lesions and in some varieties of brain tumor. Computerized tomography With the advent of computerized axial tomography (CAT or CT scanning), ever more detailed anatomic images of the brain became available for diagnostic and research purposes. The names of William H. Oldendorf (in 1961) Godfrey Newbold Hounsfield and Allan McLeod Cormack (in 1973) are associated with this revolutionary innovation, which enabled much easier, safer, non-invasive, painless and (to a reasonable extent) repeatable neuro-investigation. Cormack and Hounsfield won the Nobel Prize in Physiology or Medicine in 1979 for this work. Radioactive neuroimaging Early techniques such as xenon inhalation provided the first blood flow maps of the brain. Developed in the early 1960s by Niels A. Lassen, David H. Ingvar and Erik Skinhøj in southern Scandinavia it used the isotope xenon-133. Later versions would have 254 scintillators so a two-dimensional image could be produced on a color monitor. It allowed them to construct images reflecting brain activation from speaking, reading, visual or auditory perception and voluntary movement. The technique was also used to investigate, e.g., imagined sequential movements, mental calculation and mental spatial navigation. Soon after the invention of CAT, the development of radioligands started the functional imaging revolution. Radioligands either remain within the blood stream or enter the brain and bind to receptors. Radioligands are either single photon or positron emitters. This is how single photon emission computed tomography (SPECT) and positron emission tomography (PET) got their names. While the first human positron imaging device was developed by Gordon Brownell and William Sweet in the 1950s, Michel Ter-Pogossian, Edward J. Hoffman and Michael Phelps developed the first human PET scanner in 1973 with hexagonal detectors. After the work Marcus Raichle and coworkers, functional imaging took a large step forward with the development of oxygen-15 labelled water (H215O, or H2O-15) imaging. H2O-15 emits positrons and creates images based on regional blood flow within the brain. Since active neurons recruit a robust blood supply, H2O-15 PET allowed investigators to make regional maps of brain activity during various cognitive tasks. Later, a more common sort of functional imaging based on PET scans used FDG, a positron-emitting sugar-derivative which is distributed in the brain according to local metabolic activity. Unlike the short half-life of oxygen-15 (2.25 minutes), the 110 minute half-life of FDG allowed PET