%0 Journal Article %J Journal of Chemical Physics %D 2009 %T Shimmed matching pulses: Simultaneous control of rf and static gradients for inhomogeneity correction %A Franck, J. M. %A Demas, V. %A Martin, R. W. %A Bouchard, L. S. %A Pines, A. %K design %X

Portable NMR systems generally suffer from poor field homogeneity and are therefore used more commonly for imaging and relaxation measurements rather than for spectroscopy. In recent years, various approaches have been proposed to increase the sample volume that is usable for spectroscopy. These include approaches based on manual shimming and those based on clever combinations of modulated radio frequency and gradient fields. However, this volume remains small and, therefore, of limited utility. We present improved pulses designed to correct for inhomogeneous dispersion across wide ranges of frequency offsets without eliminating chemical shift or spatial encoding. This method, based on the adiabatic double passage, combines the relatively larger corrections available from spatially matched rf gradients [C. Meriles , J. Magn. Reson. 164, 177 (2003)]. with the adjustable corrections available from time-modulated static field gradients [D. Topgaard , Proc. Natl. Acad. Sci. U.S.A. 101, 17576 (2004)]. We explain the origins of these corrections with a theoretical model that simplifies and expedites the design of the pulse waveforms. We also present a generalized method for evaluating and comparing pulses designed for inhomogeneity correction. Experiments validate this method and support simulations that offer new possibilities for significantly enhanced performance in portable environments.

%B Journal of Chemical Physics %V 131 %8 Dec 21 %@ 0021-9606 %G English %U ://WOS:000273036300030 %N 23 %M WOS:000273036300030 %! Shimmed matching pulses: Simultaneous control of rf and static gradients for inhomogeneity correction %R Doi 10.1063/1.3243850 %0 Journal Article %J Journal of Magnetic Resonance %D 2007 %T Design and construction of a contactless mobile RF coil for double resonance variable angle spinning NMR %A Qian, C. Q. %A Pines, A. %A Martin, R. W. %K magnetism %X

Variable angle spinning (VAS) experiments can be used to measure long-range dipolar couplings and provide structural information about molecules in oriented media. We present a probe design for this type of experiment using a contactless resonator. In this circuit, RF power is transmitted wirelessly via coaxial capacitive coupling where the coupling efficiency is improved by replacing the ordinary sample coil with a double frequency resonator. Our probe constructed out of this design principle has shown favorable properties at variable angle conditions. Moreover, a switched angle spinning correlation experiment is performed to demonstrate the probe's capability to resolve dipolar couplings in strongly aligned molecules. (c) 2007 Elsevier Inc. All rights reserved.

%B Journal of Magnetic Resonance %V 188 %P 183-189 %8 Sep %@ 1090-7807 %G English %U ://WOS:000249750800020 %N 1 %M WOS:000249750800020 %! Design and construction of a contactless mobile RF coil for double resonance variable angle spinning NMR %R Doi 10.1016/J.Jmr.2007.06.006 %0 Journal Article %J Review of Scientific Instruments %D 2007 %T Multipole shimming of permanent magnets using harmonic corrector rings %A Jachmann, R. C. %A Trease, D. R. %A Bouchard, L. S. %A Sakellariou, D. %A Martin, R. W. %A Schlueter, R. D. %A Budinger, T. F. %A Pines, A. %K field %X

Shimming systems are required to provide sufficient field homogeneity for high resolution nuclear magnetic resonance (NMR). In certain specialized applications, such as rotating-field NMR and mobile ex situ NMR, permanent magnet-based shimming systems can provide considerable advantages. We present a simple two-dimensional shimming method based on harmonic corrector rings which can provide arbitrary multipole order shimming corrections. Results demonstrate, for example, that quadrupolar order shimming improves the linewidth by up to an order of magnitude. An additional order of magnitude reduction is in principle achievable by utilizing this shimming method for z-gradient correction and higher order xy gradients. (c) 2007 American Institute of Physics.

%B Review of Scientific Instruments %V 78 %8 Mar %@ 0034-6748 %G English %U ://WOS:000245320800056 %N 3 %M WOS:000245320800056 %! Multipole shimming of permanent magnets using harmonic corrector rings %R Doi 10.1063/1.2713438 %0 Journal Article %J Magnetic Resonance in Medicine %D 2005 %T High-resolution nuclear magnetic resonance spectroscopy of biological tissues using projected magic angle spinning %A Martin, R. W. %A Jachmann, R. C. %A Sakellariou, D. %A Nielsen, U. G. %A Pines, A. %K field %X

High-resolution NMR spectra of materials subject to anisotropic broadening are usually obtained by rotating the sample about the magic angle, which is 54.7 degrees to the static magnetic field. In projected magic angle spinning (p-MAS), the sample is spun about two angles, neither of which is the magic angle. This provides a method of obtaining isotropic spectra while spinning at shallow angles. The p-MAS experiment may be used in situations where spinning the sample at the magic angle is not possible due to geometric or other constraints, allowing the choice of spinning angle to be determined by factors such as the shape of the sample, rather than by the spin physics. The application of this technique to bovine tissue samples is demonstrated as a proof of principle for future biological or medical applications.

%B Magnetic Resonance in Medicine %V 54 %P 253-257 %8 Aug %@ 0740-3194 %G English %U ://WOS:000230765700001 %N 2 %M WOS:000230765700001 %! High-resolution nuclear magnetic resonance spectroscopy of biological tissues using projected magic angle spinning %R Doi 10.1002/Mrm.20585 %0 Journal Article %J Magnetic Resonance Imaging %D 2005 %T NMR in rotating magnetic fields: magic-angle field spinning %A Sakellariou, D. %A Meriles, C. A. %A Martin, R. W. %A Pines, A. %K samples %X

Magic-angle sample spinning is one of the cornerstones in high-resolution NMR of solid and semisolid materials. The technique enhances spectral resolution by averaging away rank 2 anisotropic spin interactions, thereby producing isotropic-like spectra with resolved chemical shifts and scalar couplings. In principle, it should be possible to induce similar effects in a static sample if the direction of the magnetic field is varied (e.g., magic-angle rotation of the B-0 field). Here we will review some recent experimental results that show progress toward this goal. Also, we will explore some alternative approaches that may enable the recovery of spectral resolution in cases where the field is rotating off the magic angle. Such a possibility could help mitigate the technical problems that render difficult the practical implementation of this method at moderately strong magnetic fields. (c) 2005 Elsevier Inc. All rights reserved.

%B Magnetic Resonance Imaging %V 23 %P 295-299 %8 Feb %@ 0730-725X %G English %U ://WOS:000228658400030 %N 2 %M WOS:000228658400030 %! NMR in rotating magnetic fields: magic-angle field spinning %R Doi 10.1016/J.Mri.2004.11.067 %0 Journal Article %J Journal of Physical Chemistry A %D 2004 %T NMR studies of C-13-iodomethane: Different behavior in thermotropic and lyotropic liquid crystals %A Shahkhatuni, A. G. %A Shahkhatuni, A. A. %A Panosyan, H. A. %A Park, G. H. J. %A Martin, R. W. %A Pines, A. %K biomolecules %X

High-resolution NMR spectra of C-13-iodomethane dissolved in thermotropic and lyotropic liquid crystalline solvents have been used to measure H-1-H-1 and C-13-H-1 dipolar couplings. The ratio of these two couplings, which is a function of the H-C-H bond angle in C-13-iodomethane, is, in general, different from that expected from the known molecular structure; solvent-solute interactions in liquid crystalline solutions are responsible for this difference. In thermotropic liquid crystalline solutions, the apparent bond angle deviation (Deltatheta(a)) increases with decreasing molecular ordering. In contrast, in lyotropic liquid crystals, no significant spectral aberration has been observed. These results indicate a fundamental physicochemical difference between the intermolecular interactions that prevail in thermotropic and lyotropic liquid crystals.

%B Journal of Physical Chemistry A %V 108 %P 6809-6813 %8 Aug 19 %@ 1089-5639 %G English %U ://WOS:000223289700001 %N 33 %M WOS:000223289700001 %! NMR studies of C-13-iodomethane: Different behavior in thermotropic and lyotropic liquid crystals %R Doi 10.1021/Jp047330g %0 Journal Article %J Proceedings of the National Academy of Sciences of the United States of America %D 2004 %T "Shim pulses" for NMR spectroscopy and imaging %A Topgaard, D. %A Martin, R. W. %A Sakellariou, D. %A Meriles, C. A. %A Pines, A. %K acquisition %X

A way to use adiabatic radiofrequency pulses and modulated magnetic-field gradient pulses, together constituting a "shim pulse," for NMR spectroscopy and imaging is demonstrated. These pulses capitalize on phase shifts derived from probe gradient coils to compensate for nonlinear intrinsic main magnetic field homogeneity for spectroscopy, as well as for deviations from linear gradients for imaging. This approach opens up the possibility of exploiting cheaper, less-than-perfect magnets and gradient coils for NMR applications.

%B Proceedings of the National Academy of Sciences of the United States of America %V 101 %P 17576-17581 %8 Dec 21 %@ 0027-8424 %G English %U ://WOS:000225951500004 %N 51 %M WOS:000225951500004 %! "Shim pulses" for NMR spectroscopy and imaging %R Doi 10.1073/Pnas.0408296102 %0 Journal Article %J Chemical Physics Letters %D 2004 %T Variable angle spinning (VAS) NMR study of solvent effects in liquid crystalline solutions of C-13-iodomethane %A Park, G. H. J. %A Martin, R. W. %A Sakellariou, D. %A Pines, A. %A Shahkhatuni, A. G. %A Shahkhatuni, A. A. %A Panosyan, H. A. %K phases %X

NMR spectra of C-13-iodomethane oriented in three different liquid crystalline solvents have been collected and analyzed under spinning at various angles with respect to the static magnetic field. For each sample the ratio of homonuclear (H-1-H-1) to heteronuclear (C-13-H-1) dipolar couplings, which is a function of the geometry of the solute molecule, does not change significantly with the scaling of the dipolar couplings due to spinning at different angles. This result implies that the 'apparent bond angle deviations' (Deltatheta(a)), previously calculated from thermotropic liquid crystals, arise from a solvent effect and are not an artifact from scaling the anisotropic interactions. (C) 2004 Elsevier B.V. All rights reserved.

%B Chemical Physics Letters %V 399 %P 196-199 %8 Nov 21 %@ 0009-2614 %G English %U ://WOS:000225324400036 %N 1-3 %M WOS:000225324400036 %! Variable angle spinning (VAS) NMR study of solvent effects in liquid crystalline solutions of C-13-iodomethane %R Doi 10.1016/J.Cplett.2004.10.009 %0 Journal Article %J Chemical Physics Letters %D 2003 %T High-resolution NMR of anisotropic samples with spinning away from the magic angle %A Sakellariou, D. %A Meriles, C. A. %A Martin, R. W. %A Pines, A. %K axis %X

High-resolution NMR of anisotropic samples is typically performed by spinning the sample around an axis at the magic angle of 54.7degrees with the static magnetic field. Geometric and engineering constraints often prevent spinning at this specific angle. Implementations of magic angle field rotation are extremely demanding due to power requirements or an inaccessible geometry. We present a methodology for taking the magic out of MAS while still obtaining both isotropic and anisotropic spectral information during sample spinning or field rotation at arbitrary angles. Using projected-MAS, we obtained resolved scaled isotropic chemical shifts in inhomogeneously broadened spinning samples. Published by Elsevier B.V.

%B Chemical Physics Letters %V 377 %P 333-339 %8 Aug 15 %@ 0009-2614 %G English %U ://WOS:000184895200012 %N 3-4 %M WOS:000184895200012 %! High-resolution NMR of anisotropic samples with spinning away from the magic angle %R Doi 10.1016/S0009-2614(03)01149-7