Varian Associates, Inc.

Spectrospin Ag

Richard R Ernst

Kurt Wuthrich

Walter P Aue

Slobodan Macura

For recording three-dimensional nuclear magnetic resonance spectra the nuclear spin-system must be excited by three 90.degree. pulses, with variation of the pulse intervals t.sub.1 and t.sub.m. Instead of varying the two pulse intervals separately, which would be required for recording the two time dimensions defined by t.sub.1 and t.sub.m, the mixing time t.sub.m is simultaneously varied proportionally to the evolution period each time the measurement is repeated with a varied evolution period t.sub.1, so that t.sub.m =.kappa.t.sub.1. K is so selected that the interesting mixing time period is completely covered by the predetermined number of measurements taken with different evolution times. The variation of t.sub.m is reflected by the shape of the resonance lines and can be determined also by reverse transformation of the individual resonance lines into the time domain. A spectrometer for carrying out this method may conveniently be adapted to permit setting of the pulse interval t.sub.1 and the proportionality factor K, to form therefrom automatically the second pulse interval t.sub.m.

Method for recording three-dimensional nuclear magnetic resonance

In recording two-dimensional nuclear magnetic resonance spectra, J cross peaks which hinder the interpretation of the spectragram and mask cross peaks of incoherent exchange processes or transfers are eliminated by one of two methods. In the first method, for each repetition of a measurement with an evolution period t.sub.1 between the first and second of two successive 90 degree pulses, the interval between the second and third 90 degree pulse (mixing time t.sub.m) is varied systematically in proportion to the evolution period. The two-dimensional spectra obtained is subjected to triangular multiplication or symmetrization so that all peaks which do not possess counterparts at the mirror symmetry positions of the main diagonal are eliminated. In the second method, the mixing time is kept constant and a 180 degree pulse is inserted between the second and third 90 degree pulse with a varying interval t.sub.p between the 180 degree pulse and the second 90 degree pulse for each repetition of a measurement. A spectrometer for carrying out this method permits critical parameters to be adjusted.

Method for recording two-dimensional nuclear magnetic resonance spectra

A method for the recording of spin resonance spectra, in which the spins of a nuclear species of a sample located in a magnetic field are excited by a pulsed rf signal and the relaxation oscillations of the spins are repetitively sampled and recorded at predetermined times and in which a radio-frequency decoupling signal is irradiated upon the sample to reduce coupling to the spins of another nuclear species, is characterized in that the decoupling signal consists of a periodic sequence of pulse groups comprising several pulses each, the pulses being so short that the frequency mixture detectable in the pulses according to the Fourier analysis covers the entire range of spin resonances of the other nuclear species.

Method for the recording of spin resonance spectra and an apparatus for

A method is disclosed for highly sensitive indirect detection of nuclear magnetic resonance of nuclei having a low gyromagnetic ratio using pulse techniques. The method employs a coherent transfer of transverse magnetization from the nuclei of interest to nuclei of high gyromagnetic ratio for which the free induction decay, S (t.sub.2), is observed as a function of the length of the time interval, t.sub.1, between imposition of transverse magnetization upon the nuclei of interest and transfer of magnetization to the observed nuclei. Contribution to the observed resonances not arising from the transferred transverse magnetization is eliminated and the resulting function S (t.sub.1, t.sub.2) is double Fourier transformed to the frequency domain and displayed as a two dimensional plot for resolving the multiplet spectral structure of the spectra of the nuclei having such low gyromagnetic ratio.

Indirect detection of magnetic resonance by heteronuclear

Selected orders of multiple quantum transitions may be detected by preparing a statistical non-equilibrium state of an assembly of gyromagnetic resonators of selected phase with respect to a subsequent mixing pulse. After an evolution period, t.sub.1, a 90.degree. mixing pulse is applied and the free induction decay is sampled as a function of time, t.sub.2. The signal functions S.sub.i (t.sub.1, t.sub.2, .phi..sub.i) is developed for systematically varied values of t.sub.1 and specially selected values of .phi..sub.i. Linear combinations of the signal functions S.sub.i yield, after Fourier transformation a two dimensional spectrum of multiple quantum transitions limited by the choice of phase and linear combination. In another embodiment, a magnetic gradient pulse is applied during the evolution period and resulting multiple quantum transitions yield spectral peaks of width dependent upon the order of such transitions. In particular, all spectral peaks may be removed from resulting spectra save only zero order transitions.

Selective detection of multiple quantum transitions in nuclear magnetic

An improved technique is disclosed for forming two- or three-dimensional images of a macroscopic sample by means of gyromagnetic resonance. A train of free induction decay transient resonance signals are induced and detected from a sample in a region to be imaged. A sequence of pulsed magnetic field gradients are applied during the series of free induction decay signals to derive sets of gyromagnetic resonance data as a function of the changing magnetic field gradients. Two- or three-dimensional images are reconstructed from the sets of resonance data by two- or three-dimensional Fourier transformation.

Gyromagnetic resonance fourier transform zeugmatography

A method of gyromagnetic resonance spectroscopy is disclosed which simplifies the resultant spectra by eliminating spin-spin coupling effects. The method is particularly useful for eliminating homonuclear spin-spin coupling effects. In the method, spin echo resonance of the resonators is obtained and the time elapsing between tipping of the resonators and detection of the resultant echo t.sub.1 is changed from one measurement to the next. The resultant echos are measured at equal intervals of time t.sub.2. Echo resonance data is Fourier transformed from the time domain into the frequency domain to obtain spectral data in the frequency domain as a function of t.sub.1. A second Fourier transform of the resonance data is then effected to transform the spectral data into data which is a function of both .omega..sub.1 and .omega..sub.2 where .omega..sub.1 and .omega..sub.2 are each related to 1/t.sub.1 and 1/t.sub.2, respectively. The spectral data in the .omega..sub.1 -.omega..sub.2 plane is then projected at 45.degree. to the .omega..sub.2 and .omega..sub.1 axes to derive spectral data free of spin-spin coupling effects. The data may also be projected perpendicular to and onto the .omega..sub.1 axis to obtain a J coupling spectrum.

Gyromagnetic resonance spectroscopy employing spin echo spin-spin

The multiplet spectral structure produced by coupled gyromagnetic resonators, such as heteronuclear coupling, is resolved by inducing a train of transient free induction decay (FID) resonances of a first group of gyromagnetic bodies, such as carbon-13 nuclei coupled to a second group of gyromagnetic bodies, such as protons, and detecting the FID resonance. A decoupling r.f. magnetic field is applied to the second group during free induction decay resonance of the first group for decoupling the spins of the first and second groups during detection of resonance of the first group. The duration of the decoupling effect is changed from one successive free induction decay resonance to the next and the detected resonance data is stored as a function of the change in the decoupling effect. The detected resonance data which is a function of two time intervals is then double Fourier transformed into the frequency domain and displayed as a two dimensional plot for resolving the multiplet structure of the spectra of the first group of gyromagnetic bodies.

Two dimensional gyromagnetic resonance spectroscopy

A nuclear magnetic resonance Fourier transform spectrometer includes a pulse modulated rf transmitter for delivering a train of radio frequency pulses having a pulse width pulse repetition rate to generate Fourier side bands to cover the spectral lines of the sample to be analyzed for exciting resonance of different resonance lines, if any, within the sample. Resonance of the sample is scanned in between successive transmitted pulses to obtain a multiplicity of successive time displaced components which are sampled and stored in a multiplicity of memory channels of a computer for time averaging thereof. The time averaged signal components are periodically read out and Fourier transformed to obtain a time averaged spectrum of the sample under analysis. Anomalous phase and intensity effects in the detected spectral lines are avoided by periodically shifting the phase of the pulse modulated carrier signal from one phase to another of at least three different relative phases in accordance with a predetermined sequence.

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Winterthur, Switzerland

Richard R Ernst