But it's living tissue that holds the most promise for this method, Wind said, because there is no good way to see what is happening in many areas of the body, especially at the boundaries of organs and tissues and bone or air cavities such as lungs and sinuses. Here, the large magnet used in NMR generates small magnetic fields that broaden the spectral lines so much that information about those fine details is lost.
Wind's slow-spin technique, which can generate detailed spectra from these boundary regions, takes advantage of a quirk in NMR. NMR generates a spectral signature of compounds in a sample based on the frequencies of the sample's atomic nuclei as they jiggle in a strong magnetic field. NMR pioneers noticed more than a half-century ago that they could get better spectral resolution if they spun a sample at a 54.74-degree angle to the magnetic field. The faster they spun a sample oriented in this so-called magic angle, the more structural detail they obtained.
"This was very fast spinning, an ultra-centrifuge, thousands of rotations per second," Wind said. "If you tried that with intact tissue or a live animal, you'd blow up your bio-sample and kill the subject."
But what if you could slow the spinning down, so that a live animal could withstand the centrifugal force? The problem with slow MAS is that it produced unwanted signals, what Wind and colleagues call "spinning side bands," that obscured the sample's spectra.
Wind let the idea percolate for about six years as he worked on a combined NMR-optical microscope other devices at the W.R. Wiley Environmental Molecular Sciences Laboratory on PNNL's Richland, Wash., campus. When he came at the problem again, he brought reinforcements, most notably in the person of NMR expert and PNNL staff scientist Jian Z. Hu.
Working with Hu, Wind found he could get detailed spectra in biological samples at record-slow MAS speeds by us
Contact: Bill Cannon
DOE/Pacific Northwest National Laboratory