Development of open and closed mobile NMR sensors generating highly homogenous magnetic fields
Final Report Abstract
NMR systems based on magnets build from permanent magnetic materials offer a number of advantages in terms of system mobility, maintenance, robustness and cost compared to standard superconducting magnets. Moreover they can be miniaturized in an easier way since they do not required cryo-cooling. However, in the last decades such magnets have been commercialized as so-called “time-domain” systems only suitable for relaxation and diffusion measurements. Although high-resolution spectroscopy has been achieved in the sixties and seventies with permanent magnets (like the model T-60 from varian) the size of those magnets is comparable to the one of superconducting magnets today. Shrinking the magnet has systematically led to ruin the field homogeneity achieved in standard sample volumes. To achieve spectroscopy resolution in desktop magnets a reduction of the sample volumes more than three orders of magnitude is required which seriously compromises the signal-to-noise ratio of the system. The issues limiting the achievable field homogeneity are imposed by the physical properties of the magnetic material and mechanical errors in size and positioning of the magnet blocks in the array, which are of the order of few percents (1% = 10000 ppm). The main goal of this project has been to develop a shimming strategy that can be applied to permanent magnets in order to recover the field homogeneity predicted by the simulations. Assuming that the magnet array is built from imperfect pieces, the errors can be corrected by moving at least some of the blocks composing the array. To implement this strategy in an efficient way we needed, first, to work out a compact magnet geometry that does not lose efficiency when blocks are moved. Second, to implement a numerical procedure to calculate the magnetic field quick and accurately. Third, to develop a fast field mapping method to measure the magnetic field inhomogeneities with high accuracy. Once these main steps were fulfilled the goal was set to build the smallest magnet still generating a homogeneous spot to fit standard 5-mm NMR tubes. The high sensitivity achieved by keeping the sample volume as large as in conventional high-field machines and the high-resolution achieved with the proposed shimming method has proven to boost the performance of small magnets several orders of magnitude. Weighing only 500 grams, the magnet prototype built in the project can be carried to where needed, and the NMR measurements can be performed on demand at zero maintenance cost of the device. This was demonstrated by installing the setup in a chemistry fume hood to follow reactions online. The novel magnet array developed in this project was scaled up to build a desktop MRI tomograph working on samples 40 mm in diameter. The technological development achieved in this project is of high commercial interest and has been patented by the RWTH. Today several companies are competing hard to establish ultra compact high resolution NMR as a routine method in the chemistry lab.
Publications
- Compact Magnet Array for High-Resolution NMR and MRI with Portable Sensors, The 10th International Conference on Magnetic Resonance Microscopy, West Yellowstone, Montana, USA, September 2009
Ernesto Danieli , Juan Perlo, Federico Casanova, and Bernhard Blümich
- NMR with small magnets and well defined fields, EUROMAR 2009, Göteborg, Sweden, July 2009
B. Blümich, F. Casanova, E. Danieli, and J. Perlo
- NMR with small magnets, SMASH, Chamonix, France, September 2009
B. Blümich, F. Casanova, E. Danieli, and J. Perlo
- "Magnet arrangement and method for providing a magnetic field in a sensitive volume”, US 20100013473. 2010
Blumich; Bernhard; Danieli; Ernesto Pablo; Casanova; Federico; Perlo; Juan Francisco
- Determining object boundaries from MR images with sub-pixel resolution: Towards in-line inspection with a mobile tomography, J. Magn. Reson. 207 (2010) 53-58
E. Danieli, K. Berdel, J. Perlo, W. Michaeli, U. Masberg, B. Blümich, and F. Casanova
- Halbach arrays for NMR and MRI, 32-nd discussion meeting from GDCH- Fachgruppentagung: Magnetische Resonanzspektroskopie, Münster, Germany, September 2010
F. Casanova, E. Danieli, J. Perlo, and B. Blümich
- Halbach Arrays for NMR and MRI, The 10th Bologna Conference on Magnetic Resonance in Porous Media (MRPM10) Leipzig, Germany, September 2010
J. Perlo, E. Danieli, B. Blümich, and F. Casanova
- Small Magnets for Portable NMR Spectrometers, Angew. Chem. Int. Ed. 49 (2010) 4133- 4135
E. Danieli, J. Perlo, B. Blümich, and F. Casanova
- Temperature-compensated portable magnet built from permanent magnetic materials, The 10th Bologna Conference on Magnetic Resonance in Porous Media (MRPM10) Leipzig, Germany, September 2010
E. Danieli, J. Perlo, B. Blümich, and F. Casanova
- “Segmented ring magnet arrangement for providing a magnetic field”, EP 2144076 A1. 2010
Blumich; Bernhard; Danieli; Ernesto Pablo; Casanova; Federico; Perlo; Juan Francisco
- Desktop Magnetic resonance tomograph, Fifth International Symposium on the Separation and Characterization of Natural and Synthetic Macromolecules, Amsterdam, The Nederland, January 2011
F. Casanova, E. Danieli, J. Perlo, and B. Blümich
- Highresolution NMR spectroscopy under the fume hood, Phys. Chem. Chem. Phys., 13 (2011) 13172
Simon K. Küster, Ernesto Danieli, Bernhard Blümich and Federico Casanova
- ‘Single-sided NMR’, Springer, Manheim, 2011, Chap. 2, 4, 5 and 7
F. Casanova, J. Perlo and B. Blümich
- 2012, Mobile Nuclear Magnetic Resonance, Encyclopedia of Magnetic Resonance, John Wiley & Sons
E. Danieli, B. Blümich, and F. Casanova
- Low gradient single-sided NMR sensor for one-shot profiling of human skin, J. Magn. Reson. 215 (2012) 74–84
Maxime Van Landeghem, Ernesto Danieli, Juan Perlo, Bernhard Blümich, Federico Casanova
(See online at https://doi.org/10.1016/j.jmr.2011.12.010)
