You or someone you know has probably had an internal malady examined with a magnetic resonance imaging (MRI) machine. Lying in the claustrophobic confines of the room-size magnetic doughnuts that make MRI possible can be stressful, but the diagnostic value of the resulting high-contrast pictures of the various soft tissues inside the body makes up for any angst. A more generalized version of the technique, nuclear magnetic resonance (NMR), also offers enormous benefits, enabling scientists to characterize the chemical compositions of materials as well as the structures of proteins and other important biomolecules without having to penetrate the objects under study physically.
But doctors and scientists have long yearned for portable NMR devices that could be used outside the laboratory. They have envisioned, for example, paramedics using a helmetlike MRI scanner to pinpoint blood clots in the brain of a stroke victim while still inside a speeding ambulance. And they have imagined a handheld NMR spectroscope that could discern the chemical makeup of pigments, thus permitting art experts to distinguish old-master paintings hanging in museums and galleries from modern fakes.