First steps toward micro-imaging: NMR procedure with a 10-fold increase in sensitivity developed by the CEA

D. Sakellariou (SCM), G. Le Goff et J.-F. Jacquinot (SPEC)

Nuclear magnetic resonance (NMR) is an indispensable technique for studying matter. It can be applied to medical imaging (MRI) to obtain 2D and 3D images of the human body. While it opens the door to a wealth of physicochemical information by harnessing the fundamental properties of matter, NMR remains a technique with poor sensitivity, making it very difficult to use on small quantities of solid or heterogeneous material. A group of scientists from the CEA research department dedicated to condensed matter, atoms and molecules (DRECAM) is pushing back this limit by using miniaturised mobile detectors to capture the NMR signal with high resolution and a 10-fold increase in sensitivity for sample volumes of a few hundred nanolitres.

To increase in sensitivity on small samples, it is necessary to approach as much as possible the detector (coils surrounding the sample). So, the difficulty to obtain a spectrum high resolution seems insurmountable since it would be necessary to place the sample in a micro-capillary tube and then spun at several thousand revolutions per second in a stable and reproducible way inside a micro-detector (coil) with an interior diameter of a few hundred microns. To meet this challenge, the CEA team (D. Sakellariou, G. LeGoff and J.-F. Jacquinot) came up with an innovative solution by spinning the micro-detector (coil) and sample in one piece, with power to the detector supplied via induction from an exterior coil, which also enabled the (wireless) transmission of the desired signal. The whole system spins at thousands of revolutions per second, and probably constitutes the world’s fastest set of rotating antennas.

Left: Diagram of the MACS system. Right: Proton NMR spectrum obtained on 300 µg of biological tissue in 33 seconds. Spectral signatures for metabolites are rapidly identified. The sensitivity achieved is around 20 times that of a standard 7-mm NMR detector.

The method proposed is very general and easy to implement in most commercial NMR probes, making it possible to accelerate data acquisition while reducing the minimum quantities of material required. The solution based on rotating micro-coils (MACS or magic angle coil spinning) will be enhanced by the latest miniaturisation techniques and should lead to considerable advances in NMR and micro-imaging (MRMI) as well as metabonomic and biomedical applications (on small biopsies or a few cells) and material science developments. This technique may also pave the way to NMR studies of samples from within containments (e.g. radioactive materials, high-pressure systems).

References:

[1] D. Sakellariou, G. Le Goff et J.-F. Jacquinot,
High-resolution, high-sensitivity NMR of nanolitre anisotropic samples by coil spinning,
Nature 447 (2007) XXX.

[2] D.L. Olson, T.L. Peck, A.G. Webb, R.L. Magin, and J.V. Sweedler
High-Resolution Microcoil 1H-NMR for Mass-Limited, Nanoliter-Volume Samples
Science, 270 , 1967-1970 (1995).

[3] I. Farnan, H. Cho, W. J. Weber,
Quantification of actinide $$-radiation damage in minerals and ceramics,
Nature, 445 , 190-193 (2007).

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