In 1952, the Nobel Prize in Physics was awarded for the discovery of nuclear magnetic resonance, which laid the groundwork for one of the most unique and important inventions in medical imaging since the discovery of the X-ray.

Magnetic resonance imaging (MRI) is a method of looking inside the body without using surgery, harmful dyes or radiation. The method uses magnetism and radio waves to produce clear pictures of the human anatomy.

Although MRI is used for medical diagnosis, it uses a physics phenomenon discovered in the 1930s in which magnetic fields and radio waves, both harmless to humans, cause atoms to give off tiny radio signals. In the 1940s, research physicists found that the length of time these response signals are emitted after an atom is stimulated by radio waves varies widely depending upon the substance being examined. This amazing phenomenon also holds true for biological tissue.

It wasn't until 1970, however, that Raymond Damadian, a medical doctor and research scientist, discovered the basis for using magnetic resonance as a tool for medical diagnosis when he found that different kinds of animal tissue emit response signals of differing length. He also discovered differences in response signals between cancerous and non-cancerous tissue, and among the response times of other kinds of diseased tissue.

In the early 1980s, MRI caught the attention of clinicians by its ability to visualize abnormalities in sections of the brain and in the upper cervical spine. Over the next few years, MRI became a supplementary method of diagnostic imaging in central nervous system investigations, complementing computer tomography (CT), a previously established technique that uses X-rays.

MRI played a small part in the other regions of the body. But MRI examinations took as long as two hours for each patient, and, except for the head and the spine which can be fixed and prevented from movement, MRI images from the chest and abdomen were blurred due to respiratory and heart motion.

Many of the problems encountered were from the use of low-field strength magnets and the limits of the prevailing technology of the time. However, with the introduction of high-field magnets in the mid-1980s came faster scan times and better techniques, and soon MRI was the superior choice over CT scans.

In the last three to four years, improved computer technology in hardware and software allowed MRI to obtain better quality images in most of the body. MRI has proven to be unusually capable in the detection, localization, and assessment of the extent and character of disease in the central nervous, musculoskeletal, and cardiovascular systems. In the brain for example, MRI has a proven ability to define some tumors and the plaques of multiple sclerosis better than any other technique.

MRI provides information that differs from other imaging modalities. One of its major technological advantages is that it can characterize and discriminate among tissues using their physical and biochemical properties, such as water, iron, fat, and blood. Blood flow, cerebrospinal fluid flow, and contraction and relaxation of organs, both physiologic and pathologic, can all be evaluated. Also, because calcium emits no signal on MRI images, tissues surrounded by bone, such as the contents of the head and the spine, can be seen and evaluated more clearly than with other diagnostic methods.

Another advantage is MRI produces high-resolution sectional images in multiple planes without moving the patient. This ability makes it versatile offers special advantages for radiation and surgical treatment planning.

As biomedical engineers, like Shelton Caruthers, Ph.D., at the Boston Medical Center, work with physicians and technicians to develop refinements and new applications, MRI's importance in health care continues to grow at a tremendous pace. Caruthers and other biomedical engineers push the limits of image acquisition and scanning time, having achieved rates in milliseconds for some of today's most advanced machines.

Increased resolution produces exceptionally sharp and detailed pictures and help bring about new diagnostic capabilities, such as in a study to analyze brain tissue malformations in schizophrenics, where subtle changes in the volume of brain structures are in the milliliter range. Until recently, the imaging technology didn’t have sufficient resolution to detect these small changes.

Other clinical applications of magnetic resonance are expanding through development of magnetic resonance spectroscopy and functional MRI for studies of tissue metabolism and physiologic function. Although it is not yet commonly available in a clinical setting, functional MRI, or fMRI, not only has the potential to be a powerful diagnostic tool, but it also can help determine the effectiveness of new drugs and therapies. Studies on neurological disorders, such as Parkinsons and epilepsy, now benefit from fMRI's ability to view the brain as it functions, helping to zero in on which areas of the brain are responsible for tremors or a seizure.

Today, biomedical engineers are adapting MRI for guiding surgical procedures.