Symphony in a Second

 

 

Each material plays its own unique "melody," if only we know how to listen in. When molecules are exposed to a magnetic field, the atoms in it begin to spin, and each spinning atomic nucleus emits waves of electromagnetic radiation in a distinctive pattern. For scientists, each electromagnetic symphony contains the secrets for understanding the chemical and physical properties of the material.

 

To decipher those secrets, scientists employ various methods of recording the traces of the radiation emitted by the nuclei. These include nuclear magnetic resonance (NMR) and magnetic resonance imaging (MRI). Both of these techniques are non-invasive and energy-efficient, and they are favored for such chemical and physical studies as revealing the atomic structure of drug molecules. Because they don't harm living tissue, they can be used for such biological research as tracking the development of a fetal brain. There is, however, a drawback to these techniques: The low amount of energy emitted by most materials makes it hard to detect with precision; the measurements therefore may lack sensitivity compared with some other methods of analysis.

 

Prof. Lucio Frydman of the Weizmann Institute's Chemical Physics Department and Damir Blazina of Oxford Instruments Molecular Biotools Ltd. overcame this limitation by creating a method for obtaining multidimensional images of different materials at unprecedented levels of sensitivity and speed. The details were published in Nature Physics.

 

The method is based on a technique for amplifying the signal from the atomic nuclei. Dynamic nuclear hyperpolarization, as it's called, is a method for aligning the spin of the nuclei. It works something like exposing a bunch of compasses to a large magnet so that all of their needles point in the same direction. When the nuclei's spins are all attuned, their signal rises to a chorus – making it much easier to detect. Hyperpolarization can align about 20% (one in five) of the nuclear spins in a sample. That's an enormous improvement over existing NMR methods, which are capable of lining up a mere one in 50,000, at best. Hyperpolarization, however, has its own drawback: It's an exceptional state that takes a relatively long time to prepare, and it can only be sustained for a short time, basically permitting scientists to obtain no more than one "super scan" of a material.

 

To make the most of that one-time scan, the scientists combined it with a technique Frydman and his team had previously developed to speed up the process of obtaining multidimensional NMR images. Standard NMR techniques often take hours or days to complete, as successive images are recorded one at a time and then compiled. Frydman's method, called ultrafast NMR, "carves" the sample into thin slices and images them all at once.

 

The combined method should prove to be more sensitive than existing NMR techniques by several orders of magnitude, as well as many times faster. But the real excitement in this innovation, says Frydman, is in the new research possibilities that the method may open up: Many chemical and physical phenomena have so far remained beyond the reach of scientists because they take place too rapidly for existing techniques to measure them. "An ultrafast, highly sensitive technique will doubtlessly make interesting new scientific discoveries possible."