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Seeing Inside the Body

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[MRI cross-section of  brain]

An MRI Cross-Section of a brain showing both hemispheres as well as the ventricles (openings). Source: National Institute of Neurologic Disorders and Stroke

[Patient entering MRI  machine]

Patient entering a magnetic resonance imaging (MRI) machine for medical diagnosis. Source: National Cancer Institute


Over the ages, physicians have sought a means of seeing inside the human body without cutting it open. Fundamental discoveries in physics have given us first x-rays and then the more modern diagnostic methods of magnetic resonance imaging (MRI) and positron-electron tomography (PET), contributing to remarkable advances in medical research.

The development of MRI is illustrative of the often complex path to major new technologies. It began as basic research in nuclear physics--in particular, the curious fact that the nuclei of most atoms behave as though they have a tiny magnet attached to them. Physicists soon learned that when they probed the properties of that magnet with a radio beam in the presence of a strong external magnetic field, they could identify which kind of atom it was. As the technique, known as nuclear magnetic resonance, improved, it became possible even to tell something about an atom's interactions with neighboring atoms. Chemists then developed the technique further as a powerful tool for analyzing the chemical structure of a material, including, eventually, biological tissues. This ability to probe the submicroscopic structure of matter--and hence to map the distribution of certain kinds of molecules in a sample or of cancer cells in a body--provided the scientific base for MRI.

Yet MRI also depends on a number of technologies that evolved separately but in parallel with the basic science, and it was the combination of these with the fundamental physics that made MRI possible. Once the idea emerged of using the nuclear magnetic resonance technique to create images, for example, a host of practical problems remained. For one thing, the technique was initially too slow for medical use. Modern electronics--especially computers-on-a-chip that could be built directly into practical instruments--helped speed it up.

So did the mathematical technique known as tomography--synthesizing a composite image from many different "pictures." Superconducting magnets helped to make more compact and powerful MRI instruments.

The result is a remarkable medical diagnostic tool. MRI gives the most precise picture now available of what is happening inside the body and does so noninvasively and safely. Yet it is most unlikely that MRI could have emerged from a targeted effort to design a better imaging technique--who would have thought to begin by measuring the strengths of magnets within atomic nuclei? For MRI, as for many other important technologies, just such fundamental explorations of nature produced the knowledge that enabled a vision of a life-saving imaging technique.

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