scans by machines physically distant from the cyclotron producing the isotope (in this case fluorine-18). Magnetic resonance imaging Shortly after the initial development of CT, magnetic resonance imaging (MRI or MR scanning) was developed. Rather than using ionizing or X-radiation, MRI uses the variation in signals produced by protons in the body when the head is placed in a strong magnetic field. Associated with early application of the basic technique to the human body are the names of Jackson (in 1968), Damadian (in 1972), and Abe and Paul Lauterbur(in 1973). Lauterbur and Sir Peter Mansfield were awarded the 2003 Nobel Prize in Physiology or Medicine for their discoveries concerning MRI. At first, structural imaging benefited more than functional imaging from the introduction of MRI. During the 1980s a veritable explosion of technical refinements and diagnostic MR applications took place, enabling even neurological tyros to diagnose brain pathology that would have been elusive or incapable of demonstration in a living person only a decade or two earlier. Scientists soon learned that the large blood flow changes measured by H2O-15 PET were also imaged by MRI. Functional magnetic resonance imaging (fMRI) was born. Since the 1990s, fMRI has come to dominate the brain mapping field due to its low invasiveness, lack of radiation exposure, and relatively wide availability. Physicists have also developed other MRI-based techniques such as arterial spin labeling (where arterial blood is magnetically tagged before it enters into the tissue of interest and the amount of labeling is measured and compared to a control recording obtained without spin labeling), magnetic resonance spectroscopy (for measuring some key metabolites such as N-acetylaspartate and lactate within the living brain) and diffusion tensor imaging (for mapping white matter tracts within the living brain). Whereas structural MRI and CAT scanning have a large place in medicine, fMRI and its brethren techniques are still largely devoted to neuroscience research. However, very recently neurologists have started to use fMRI to begin to answer clinical questions, such as how long after thrombotic stroke is it safe and effective to give clot-dissolving drug like tissue plasminogen activator (TPA). Similarly, PET and SPECT have moved out of neuro-research and are increasingly being used clinically to help diagnose and differentiate types of dementing illnesses (dementia). Magnetoencephalography Magnetoencephalography (MEG) signals were first measured by University of Illinois physicist David Cohen in 1968,. He later used one of the first SQUID detectors, to