The foundation of nuclear magnetic resonance (NMR) imaging was laid in 1946, by Professor Felix Bloch, Professor at Stanford University, and one-time ETH physicist, and Professor Edward Mills Purcell of Harvard. They were the first to develop a way to measure the resonance absorption of atoms in static magnetic fields. For their pioneering work they were jointly awarded the Nobel Prize for physics in 1952.

The magnetic characteristics of atomic nuclei are described in physics by the term spin. The spin of an atom is determined by the spin of an atom's elementary particles (protons: spin 1/2 and neutrons: spin 0). We can imagine this spin – which can only really be accurately described with the help of quantum physics – as a small magnet. If an atom with a spin is placed in a strong magnetic field, it is aligned either parallel or anti-parallel to the magnetic field. With NMR spectroscopy the difference in energy of the two states can be measured. This energy difference has a characteristic value for each atom. Apart from the interaction of the spin with the external magnetic field, there are also interactions amongst the spins. For example, every spin produces a small magnetic field, and so influences the magnetic field at the location of another spin.

Progress – rewarded with a Nobel Prize

Great progress has been made in the past fifty years in NMR spectroscopy. With the so-called pulsed Fourier transformation, for example, a way was found to markedly improve the signal-to-noise ratio. The basis for this work was laid down by the (now retired) ETH Professor Richard R. Ernst, who received the Nobel Prize for chemistry in 1991 in recognition of his contribution to the field. Further important work was carried out by the ETH biophysicist, Professor Kurt Wüthrich, who was awarded the Nobel Prize for chemistry in 2002 for his research on the determination of three dimensional structures of biological macro-molecules. The most recent recognition of the field came with the 2003 Nobel Prize for medicine to Paul Lauterbur and Peter Mansfield for their work on magnetic resonance imaging.

Winner of this year's Ruzicka Prize: Matthias Ernst, in the NMR laboratory at Hönggerberg. large

Now a further, prestigious prize has been bestowed on NMR research: the 2003 Ruzicka Prize was awarded to Matthias Ernst from the ETH Laboratory of Physical Chemistry (1). The 39 year-old chemist was recognised for his work on spin decoupling in solid-state nuclear magnetic resonance spectroscopy under "magic-angle" sample spinning, or MAS.

MAS is a cunning contrivance. Researchers discovered that the resolution of the solid-state NMR spectrum is considerably increased if the sample is placed in the magnetic field of the instrument and rotated about an angle of 54.7 degrees. With the spin-spin decoupling, coupled signals – visible as additional lines or broad bands on the NMR monitor – can be made a lot narrower by irridating the spins with additional high-frequency pulses. Coupled signals are caused by the interaction of the spins of different atoms. To take the example of fluormethane, FCH3: without spin-spin-decoupling the spectrum of the fluorine atom is recorded as a quadruplet, a signal with four peaks. This signal describes the interaction between the H atoms with the F atom. With decoupling, by contrast, the spectrum shows just one line. "The work that has been distinguished deals with the theoretical description of this spin-decoupling in rotating samples and the development of the method to obtain higher resolution," says Matthias Ernst. The new method makes it possible to reduce the radio frequency field by a factor of 200 at very fast sample rotation frequencies with only an insignificant reduction in the spectral resolution.

Amorphous compounds can be investigated too

This method is of great importance to chemistry, physics, biology and materials science because magnetic resonance spectroscopy also enables scientists to examine, in contrast to X-ray defraction, non-crystalline structures. These include amyloids, for example, which are proteins deposited in certain diseases, such as Alzheimer's, or prions, which are found in the brains of cows infected with BSE. Only recently the Swiss National Science Foundation presented results of research on the chemical structure of spiders' web fibre that the solid-state group at ETH Zurich succeeded in decoding.