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From Structure to Function |
A phenomenal tool for imaging the anatomy and structure of living tissue, MRI was greatly enhanced in the 1980s and 1990s by the development of its ability to capture an organism in action--to study function. The breakthrough that led to functional MRI, fMRI as it is known, came in the early 1980s, when George Radda and colleagues at the University of Oxford, England, found that MRI could be used to register changes in the level of oxygen in the blood, which in turn could be used to track physiological activity. The principle behind BOLD (for blood oxygen level dependent) contrast imaging had been described some 40 years earlier by Linus Pauling. In 1936, Pauling and Charles D. Coryell, both then at the California Institute of Technology, published a paper describing the magnetism of hemoglobin, the oxygen-carrying pigment that gives red blood cells their color. Much earlier, in 1845, English physicist and chemist Michael Faraday, the discoverer of electromagnetic induction, investigated the magnetic properties of dried blood and made a note to himself: "Must try recent fluid blood." As it happened, Faraday never got around to it, leaving it to Pauling and Coryell more than 90 years later. The two chemists found that the magnetic susceptibility of fully oxygenated arterial blood differed by as much as 20 percent from that of fully deoxygenated venous blood.
In 1990, Seiji Ogawa of AT&T's Bell Laboratories reported that, in studies with animals, deoxygenated hemoglobin, when placed in a magnetic field, would increase the strength of the field in its vicinity, while oxygenated hemoglobin would not. Ogawa showed in animal studies that a region containing a lot of deoxygenated hemoglobin will slightly distort the magnetic field surrounding the blood vessel, a distortion that shows up in a magnetic resonance image.
At about the same time, other investigators also were studying these effects in humans. In 1992, for example, a number of researchers, including Ogawa, John W. Belliveau at Massachusetts General Hospital, and Peter Bandettini at the Medical College of Wisconsin, published results of studies of the brain's response to sensory stimulation using functional MRI techniques. Among other uses, fMRI currently can help guide brain surgeons away from critical areas of the brain, detect signs of stroke, and elucidate the workings of the brain.
Today what Rabi began has become a multibillion dollar industry. MRI scanning and spectroscopy are widely used diagnostic imaging technologies in medicine, and as new techniques and ever more powerful machines have come online in the past few years, the speed and precision of MRI and fMRI have increased dramatically.
None of this would have been possible without the nearly four decades of basic research following Rabi's first detection of nuclear magnetic resonance. Those decades included crucial discoveries by physicists and chemists interested in studying the magnetic properties of atoms and molecules, in seeing how they interact, and in elucidating their basic structures. As George Pake, Purcell's second graduate student, put it in 1993, "Without the basic research, magnetic resonance imaging was unimaginable." |
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 | | | Neuroscience for Kids - This site from the University of Washington offers simple explanations of some of the different kinds of imaging. |  | | Physics 2000 - This site from the Univeristy of Colorado's Physics Department is great. You can go here if you want to get an overview of physics concepts, or look at a model of the atom. | | | SpectroscopyNOW.com: MRI - This site includes several resources for information on MRI. | | | The Laboratory of Functional MRI - This site of the Memorial Sloan-Kettering Cancer Center gives you more information on the continuing research on fMRI. | | | Visible Human Project - The National Library of Medicine's Visible Human Project includes a set of MRI scans. |  |
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