OCTOBER 15--Using a technique similar to magnetic resonance imaging (MRI) widely applied by hospitals for medical diagnosis but at a resolution 10,000 times greater, physicists at Northwestern University (Evanston, IL) have gained insight into a high-temperature superconductor that might one day benefit hospital MRI technologies and the patients who rely on them. The research, led by William Halperin, professor of physics and astronomy, in collaboration with scientists from Northwestern, Argonne National Laboratory, and the National High Magnetic Field Laboratory, was reportedly the highest magnetic-field-imaging experiment ever conducted. The findings, including the direct evidence of an electronic Doppler effect, will be published in Nature.
"Currently, hospitals use low-temperature superconductors in MRI, but high-temperature superconductors--a relatively new discovery--may be a better material, with the bonus of requiring less cooling, thus reducing costs," said Halperin. To advance its potential application in future technologies, the researchers first need to understand the physical properties of these materials and especially how they behave in the presence of very large magnetic fields. "The goal in the medical world is to get better resolution in MRI technology to improve diagnoses--the better the resolution the more detail for analysis," said Halperin. "Our imaging method is a major technical advance in the study of superconductors and one that has basic implications for magnetic imaging."
For the first time, researchers were able to peer into the cores of vortices--tiny electrical tornadoes swirling around in the copper oxide compound, YBa2Cu3O7, the classic high-temperature superconducting material. (The vortices result from magnetic fields trapped inside the material.) The core of the vortex in the superconductor is very much like the eye of a hurricane except that it is so small it is hard to investigate. Each core measures only 3 nm across. Extremely high resolution--made possible by a large magnetic field--was required to look inside the vortex core.
The most important component of the MRI technology used in hospitals is the main magnet, which supplies the steady magnetic field critical for high-quality imaging. Superconducting magnets are the most widely used because they require less electricity, thus reducing the cost of operation. Also important are the gradient magnets that generate magnetic fields that vary in space. These nonuniform fields make it possible to distinguish one region of the body from another, generating three-dimensional images from any angle and direction, in a noninvasive fashion.