Slurred speech or partial paralysis may signal only a seizure or migraine but can also be symptoms of stroke. Stroke is the third leading cause of death in the United States and a primary cause of serious disability. More than 3 million people who have survived a stroke are left unable to work or to care for themselves. So when a patient enters an emergency room with these symptoms, doctors must make a crucial diagnosis with little time to delay. At a large number of hospitals, physicians can now order an image of the patient's brain, using a technique called magnetic resonance imaging (MRI). The scan can reveal within a few minutes not only whether the patient has had a stroke but also which part of the brain is in danger. The importance of this diagnosis cannot be overstated. This stroke diagnostic tool represents a major clinical application of MRI.

MRI, which provides detailed images of anatomical structure, opens a vital window on other parts of the body as well. In the heart it can detect signs of arterial sclerosis. In the spine, bones, and joints it can find ruptured disks, torn cartilage, and tumors. And in all these cases, MRI works with no harmful interventions.

Since the early 1990s, a variant of conventional MRI called functional MRI (fMRI) has been a tremendous boon to neuroscience research, helping scientists learn more about how the brain works by visualizing changes in the chemical composition of various regions or changes in the flow of fluids that occur over seconds or minutes. fMRI can also be used to increase understanding of the physiology of other organs.

The basic research that made MRI and fMRI possible began in physics laboratories in the early decades of the last century. The following article describes the often winding road that over the last 70 years has led from the work of scientists simply investigating the nature of matter to applications that would ultimately save many lives.

This article is also available in Spanish.