A Guide to Magnetic Resonance Imaging (MRI)

How Magnets and Radio Waves Changed Medicine Forever

Male patient undergoing CAT scan

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Magnetic resonance imaging (commonly called "MRI") is a method of looking inside the body without using surgery, harmful dyes, or X-rays. Instead, MRI scanners use magnetism and radio waves to produce clear pictures of the human anatomy.

Foundation in Physics

MRI is based on a physics phenomenon discovered in the 1930s called "nuclear magnetic resonance"—or NMR—in which magnetic fields and radio waves cause atoms to give off tiny radio signals. Felix Bloch and Edward Purcell, working at Stanford University and Harvard University, respectively, were the ones who discovered NMR. From there, NMR spectroscopy was used as a means to study the composition of chemical compounds.

The First MRI Patent

In 1970, Raymond Damadian, a medical doctor and research scientist, discovered the basis for using magnetic resonance imaging as a tool for medical diagnosis. He found that different kinds of animal tissue emit response signals that vary in length, and, more importantly, that cancerous tissue emits response signals that last much longer than non-cancerous tissue.

Less than two years later, he filed his idea for using magnetic resonance imaging as a tool for medical diagnosis with the U.S. Patent Office. It was entitled "Apparatus and Method for Detecting Cancer in Tissue." A patent was granted in 1974, producing the world's first patent issued in the field of MRI. By 1977, Dr. Damadian completed construction of the first whole-body MRI scanner, which he dubbed "Indomitable."

Rapid Development Within Medicine

Since that first patent was issued, the medical use of magnetic resonance imaging has developed rapidly. The first MRI equipment in health was available at the beginning of the 1980s. In 2002, approximately 22,000 MRI cameras were in use worldwide, and more than 60 million MRI examinations were performed.

Paul Lauterbur and Peter Mansfield

In 2003, Paul C. Lauterbur and Peter Mansfield were awarded the Nobel Prize in Physiology or Medicine for their discoveries concerning magnetic resonance imaging.

Paul Lauterbur, a professor of chemistry at the State University of New York at Stony Brook, wrote a paper on a new imaging technique that he termed "zeugmatography" (from the Greek zeugmo meaning "yoke" or "a joining together"). His imaging experiments moved science from the single dimension of NMR spectroscopy to the second dimension of spatial orientation—a foundation of MRI.

Peter Mansfield of Nottingham, England further developed the utilization of gradients in the magnetic field. He showed how the signals could be mathematically analyzed, which made it possible to develop a useful imaging technique. Mansfield also showed how extremely fast imaging could be achieved.

How Does MRI Work?

Water constitutes about?two-thirds?of a human's body weight, and this high water content explains why magnetic resonance imaging has become widely applicable in medicine. In many?diseases, the pathological process results in changes?in?the water content among tissues and organs, and this is reflected in the MR image.

Water is a molecule composed of hydrogen and oxygen atoms. The?nuclei of the hydrogen atoms?are able to act as microscopic compass needles. When the body is exposed to a strong magnetic field, the nuclei of the hydrogen atoms are directed into order—stand "at attention." When submitted to pulses of radio waves, the energy content of the nuclei changes. After the pulse, the nuclei return to their previous state and a resonance wave is emitted.

The small differences in the oscillations of the nuclei are detected with advanced computer processing; it is possible to build up a three-dimensional image that reflects the chemical structure of the tissue, including differences in the water content and in movements of the water molecules. This results in a very detailed image of tissues and organs in the investigated area of the body. In this manner, pathological changes can be documented.