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US 5,327,086 AGranted
Multiple-quantum NMR with frequency-modulated chirp pulses
AssigneeSpectrospin AG
InventorsGeoffrey Bodenhausen, Jean-Marc Bohlen, Irene Burghardt
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AssigneeSpectrospin AG
InventorsGeoffrey Bodenhausen, Jean-Marc Bohlen, Irene Burghardt
Estimating the term…
Frequency-modulated "chirp" pulses for exciting multiple-quantum coherences over large bandwidths can be considered as an alternative to composite pulses to combat the effects of large offsets and tilted effective fields. Refocusing of the phase dispersion of double-quantum coherence can be combined with suitable detection sequences to yield pure absorption two-dimensional double-quantum spectra. The method of symmetrical excitation and detection by time-reversal may be applied to obtain t.sub.1 -modulated longitudinal magnetization, which may then be converted into observable single-quantum coherence by a chirp echo sequence. Similar approaches can be used for many other NMR experiments involving coherence transfer.
In a method which includes the step of exciting a multiple quantum coherence in an NMR pulse experiment, said exciting step including the steps of subjecting a nuclear spin system to a magnetic field and irradiating said nuclear spin system, while subjected to said magnetic field, with a first sequence of RF pulses which includes a basic sequence having a first .pi./ 2-pulse, a first .pi.-pulse generated after a defocusing time interval .tau. following the first .pi./2-pulse, and a .pi./2-pulse generated after another time interval .tau. following the first .pi.-pulse, said method further including the step of reconverting said excited multiple quantum coherence into a transverse magnetization for inducing a free induction decay, said reconverting step including the step of irradiating said nuclear spin system with a second sequence of RF pulses;
In a method which includes the step of exciting a multiple quantum coherence in an NMR pulse experiment, said exciting step including the steps of subjecting a nuclear spin system to a magnetic field of high field strength and irradiating said nuclear spin system, while subjected to said magnetic field of high field strength, with a first sequence of RF pulses which includes a basic sequence having a first .pi./2-pulse, a first .pi.-pulse generated after a time interval .tau. following the first .pi./2-pulse, and a second .pi./2-pulse generated after another time interval .tau. following the first .pi.-pulse, said method further including the step of reconverting said excited multiple quantum coherence into a transverse magnetization for inducing a spin echo, said reconverting step including the step of irradiating said nuclear spin system with a second sequence of RF pulses;
In a method which includes the steps of exciting a multiple quantum coherence in an NMR pulse experiment, said exciting step including the steps of subjecting a nuclear spin system to a magnetic field of high field strength and irradiating said nuclear spin system, while subjected to said magnetic field of high field strength, with a first sequence of RF pulses which includes a basic sequence having a first .pi./2-pulse, a first .pi.-pulse generated after a defocusing time interval .tau. following the first .pi./2-pulse, and a second .pi./2-pulse generated after another time interval .tau. following the first .pi.-pulse, said method further including the step of reconverting said excited multiple quantum coherence into a transverse magnetization for inducing a free induction decay, said reconverting step including the step of irradiating said nuclear spin system with a second sequence of RF pulses;
In a method for exciting, by means of a first sequence of RF pulses, at least one of a multiple quantum coherence and a double quantum coherence in an NMR pulse experiment by irradiating a nuclear spin system, subjected to a magnetic field, with the first pulse sequence which includes a first .pi./2-pulse, a first .pi.-pulse generated after a defocusing time interval .tau. following the first .pi./2-pulse, and a second .pi./2-pulse generated after another time interval .tau. following the first .pi.-pulse, and for reconverting, by irradiating the nuclear spin system with a second sequence of RF-pulses, the excited multiple quantum coherence into a transverse magnetization for inducing a free induction decay, the improvement comprising wherein the three RF pulses of the first pulse sequence are chirp pulses each having a duration t.sub.p during which the frequency of the exciting RF field is swept in a monotonic fashion with respect to time between a lower frequency .omega..sub.RFmin and an upper frequency .omega..sub.RFmax and the second sequence of RF pulses includes a fourth chirp pulse with a duration t.sub.p /2 and an amplitude between 2 and 4 times the amplitude of the first .pi./2-pulse.
In a method for exciting, by means of a first sequence of RF-pulses, at least one of a multiple quantum coherence and a double quantum coherence in an NMR pulse experiment by irradiating a nuclear spin system, subjected to a magnetic field of high field strength, with the first pulse sequence which includes a first .pi./2-pulse, a first .pi.-pulse generated after a time interval .tau. following the first .pi./2-pulse, and a second .pi./2-pulse generated after another time interval .tau. following the first .pi.-pulse, and for reconverting, by irradiating the nuclear spin system with a second sequence of RF-pulses, the excited multiple quantum coherence into a transverse magnetization for inducing a spin echo, the improvement wherein the second sequence of RF pulses further includes, after a dephasing time interval .tau..sub.1 following the spin echo, a chirp refocusing .pi.-pulse having a duration t.sub.p /2 during which the frequency of the RF field is monotonically swept with respect to time between a lower frequency .omega..sub.RFmin and an upper frequency .omega..sub.RFmax, and a subsequent chirp .pi./2-pulse of duration t.sub.p.
In a method for exciting, by means of a first pulse sequence of RF pulses, at least one of a multiple and a double quantum coherence in an NMR pulse experiment by irradiating a nuclear spin system, subjected to a magnetic field of high field strength, with the first pulse sequence which includes a first .pi./2-pulse, a first .pi.-pulse generated after a defocusing time interval .tau. following the first .pi./2-pulse, and a second .pi./2-pulse generated after another time interval .tau. following the first .pi.-pulse, and for reconverting, by irradiating the nuclear spin system with a second sequence of RF pulses, the excited multiple quantum coherence into a transverse magnetization for inducing a free induction decay, the improvement wherein the three RF pulses of said first pulse sequence are chirp pulses each having a duration t.sub.p during which the frequency of the exciting RF field is swept in a monotonic fashion with respect to time between a lower frequency .omega..sub.RFmin and an upper frequency .omega..sub.RFmax and the first pulse sequence is followed, after an evolution interval t.sub.1 , by an additional pulse sequence which is a time reversed version of said first pulse sequence.
Dependencies are inferred from the claim text.