Electricity: measuring and testing – Particle precession resonance – Using a nuclear resonance spectrometer system
Patent
1992-12-11
1994-07-05
Arana, Louis
Electricity: measuring and testing
Particle precession resonance
Using a nuclear resonance spectrometer system
324309, G01V 300
Patent
active
053270860
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a method for exciting multiple-, especially double-quantum coherence in NMR pulse experiments by irradiating a nuclear spin system, subjected to a magnetic field with a first sequence of RF-pulses comprising a basic sandwich consisting of a first .pi./2-pulse, a first .pi.-pulse being generated after elapse of a defocusing time interval .tau. following the first .pi./2-pulse and a second .pi./2-pulse being generated after elapse of another time interval .tau. following the first .pi.-pulse and for reconverting said excited multiple-quantum coherence into transverse magnetization inducing a free induction decay by irradiating said nuclear spin system with a second sequence of RF-pulses.
A method of the above mentioned kind is known from the scientific publication by D. P. Weitekamp, Adv. Magn. Reson. 11,111 (1983).
Many modern NMR methods make use of the phenomenon of coherence transfer, where transverse magnetization, or more generally p-quantum coherence, is transferred from one spin (or set of spins) to another. Some of the best known examples are correlation spectroscopy and multiple-quantum NMR. Many of these experiments rely on the extensive use of so-called "hard" pulses to induce rotations of the density operator. In practice, such pulses are often not really hard enough to be truly offset-independent, so that off-resonance effects (tilted effective fields) have to be taken into consideration. In the simplest experiments, such as in correlation spectroscopy (COSY), off-resonance effects merely lead to relatively innocuous phase errors which can easily be corrected by suitable data processing.
In more sophisticated experiments however, errors in successive pulses often have a cumulative effect which may lead to a complete failure of the desired coherence transfer processes. Thus in multiple-quantum NMR according to the above citation, the coherences are excited by a sandwich of three monochromatic radio-frequency pulses (.pi./2-.tau.-.pi.-.pi./2). If the effective fields are tilted, this sandwich may fail completely. This point has been discussed in detail by Levitt and Ernst, Mol. Phys. 50, 1109 (1983), who proposed alternative sequences incorporating composite pulses. These sequences are based on the idea that several successive rotations can be designed so as to have a better overall behaviour than a single rotation. A limitation of composite pulses is that they only perform well over a limited frequency window, typically over a range of offsets comparable to the RF amplitude.
In the following, a pulse which converts the magnetization from an initial state aligned with the magnetic field to a new state, where the magnetization is orthogonal to the magnetic field, will be designated as ".pi./2-pulse", whereas a pulse which converts the transverse magnetization into transverse magnetization in such a manner that a spin-echo is formed, will be designated as ".pi.-pulse".
Like Levitt and Ernst, we shall focus attention on double-quantum spectroscopy of pairs of weakly-coupled spin 1/2 nuclei. From the point of view of spectroscopic recognition of molecular structure, one of the potentially most promising experiments of this type is the carbon-carbon correlation experiment known under the name INADEQUATE from
A. Bax et al. in J. Am. Chem. Soc. 102,4849 (1980). This method allows one to identify the entire carbon backbone of organic molecules by mere inspection of the signals in a two-dimensional spectrum. This approach would undoubtedly enjoy much greater popularity if it were not for difficulties in obtaining reliable excitation of double-quantum coherences over arbitrary spectral widths.
It is, therefore, a primary object of the invention to provide a method of the initially mentioned kind for exciting multiple-quantum coherences efficiently over wide offset ranges using RF-pulses of comparatively small amplitudes.
SUMMARY OF THE INVENTION
This object, according to one aspect of the invention, is achieved by a method, where the three RF-pulses of said basic sandwich are ch
REFERENCES:
patent: 3725773 (1973-04-01), Nelson
patent: 4238735 (1980-12-01), Muller
patent: 4703270 (1987-10-01), Hall et al.
patent: 5045790 (1991-09-01), Hall et al.
patent: 5166616 (1992-11-01), Doddrell et al.
patent: 5168229 (1992-12-01), Hurd et al.
Journal of Magnetic Resonance, vol. 64, 1985, Academic Press, Inc., (Duluth, MN, U.S.), Dumoulin: "The Application of Multiple-Quantum Techniques for the Suppression of Water Signals in .sup.1 H NMR Spectra", pp. 38-46.
Journal of Magnetic Resonance, vol. 83, No. 1, Jun. 1989, Academic Press, Inc., (Duluth, MN, U.S.), Yeung et al.: "Imaging and Localized Spectroscopy of .sup.13 C by Polarization Transfer", pp. 183-189.
J. S. Waugh (ed.), "Advances in Magnetic Resonance", vol. 11, 1983, Academic Press, (New York, U.S.).
D. P. Weitekamp: "Time-Domain Multiple-Quantum NMR", pp. 111-274.
Journal of Magnetic Resonance, vol. 84, No. 1, Aug. 1989, Academic Press, Inc., (Duluth, MN, U.S.), Bohlen et al.: "Refocusing with Chirped Pulses for Broadband Excitation Without Phase Dispersion", pp. 191-197.
Molecular Physics, vol. 50, No. 5, 1983, Levitt et al.: "Improvement of Pulse Performance in N.M.R. Coherence Transfer Experiments. A Compensated Inadequate Experiment", pp. 1109-1124.
Journal of Magnetic Resonance, vol. 87, No. 1, Mar. 1990, Academic Press, Inc., (Duluth, MN, U.S.), Wimperis: "Correlation of Connected Double-Quantum and Single-Quantum Transitions. Two-Dimensional Double-Quantum Spectroscopy . . . " pp. 174-182.
Bodenhausen Geoffrey
Bohlen Jean-Marc
Burghardt Irene
Arana Louis
Spectrospin AG
LandOfFree
Multiple-quantum NMR with frequency-modulated chirp pulses does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Multiple-quantum NMR with frequency-modulated chirp pulses, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Multiple-quantum NMR with frequency-modulated chirp pulses will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-798432