Method and apparatus for performing an NMR experiment

Claim 1

An NMR apparatus for the acquisition of magnetic resonance information from a sample comprising magnetic resonators by one or more pulses of Rf radiation comprising Rf magnetic field B 1 , said resonators subject to an effective magnetic field B in a frame of reference rotating at Rf frequency ν 0 about an axis defined by an applied dc magnetic field the effective field B a vector comprising resonance offset ΔH and the Rf magnetic field B 1 , said effective field B at an angle α with to said Rf magnetic field B 1 , comprising modulation means for controlling both the amplitude and Rf frequency of said pulse to cause said pulse to exhibit a first time dependence in amplitude over the interval defined by said pulse and further to cause said pulse to exhibit a second time dependence in radio frequency over the interval of said pulse, said time dependencies satisfying the conditions wherein (a) said effective field B is maintained substantially constant over the interval of said pulse, (b) said angle α changes over the interval of said pulse in accord with said modulation, said change comprising a rate dα/dt such that dα/dt is substantially constant over the interval of said pulse and that dα/dt is small compared to B.

Claim 16

The method of achieving spatially uniform NMR pulse excitation of a distributed sample from an Rf coil proximate the surface of said sample comprising the steps of: modulating, by a first sinusoidal function, the amplitude of an Rf pulse applied to said Rf coil to impose a time dependence of said amplitude from a selected initial value of the argument of said first sinusoidal function to a selected final argument of the value of said first sinusoidal function, modulating, in accord with a second sinusoidal function related to said first sinusoidal function by a phase difference of 90°, the frequency of said Rf pulse applied to said Rf coil to impose a time dependence of said frequency from a selected initial value of the argument of said second sinusoidal function to a selected final argument value of said second sinusoidal function.

Claim 17

The method of achieving spatially uniform NMR pulse excitation of a distributed sample from an Rf coil proximate the surface of said sample comprising the steps of: modulating, by a first sinusoidal function, the amplitude of an Rf pulse applied to said Rf coil to impose a time dependence of said amplitude from a selected initial value of the argument of said first sinusoidal function to a selected final argument of the value of said first sinusoidal function, modulating, in accord with a second sinusoidal function related to said first sinusoidal function by a phase difference of 90°, the frequency of said Rf pulse applied to said Rf coil to impose a time dependence of said frequency from a selected initial value of the argument of said second sinusoidal function to a selected final argument value of said second sinusoidal function.

Claim 19

A method of obtaining a nuclear magnetic resonance signal from a sample using a radio frequency irradiation coil which provides an inhomogeneous radio frequency magnetic field, the method comprising causing the coil to apply a radio frequency pulse to the sample in the presence of an external magnetic field, performing an adiabatic passage, and obtaining the resultant NMR signal, said adiabatic passage such that the effective field B experienced by nuclear spins within the sample is changed such that |dα/dt|<B tan α=ΔH/B 1 and B=(ΔH 2 +B 1 2 ) 1/2 =B 1 sec α, ΔH is the resonance offset of the nuclear spins, and B 1 is the Rf field of a spin-lock pulse, said Rf pulse is controlled such that: B.sub.1 =v A sin 2πνt and ΔH=A(cos 2πνt+s), where S=S/A, where S is the frequency offset of a nucleus from the center of the spectrum, and where v allows for variation of B 1 throughout the sample.

Claim 20

A method of obtaining a nuclear magnetic resonance signal from a sample using a radio frequency irradiation coil which provides an inhomogeneous radio frequency magnetic field, the method comprising causing the coil to apply a radio frequency pulse to the sample in the presence of an external magnetic field, performing an adiabatic passage, and obtaining the resultant NMR signal, said adiabatic passage such that the effective field B experienced by nuclear spins within the sample is changed such that |dα/dt|<B tan α=ΔH/B 1 and B=(ΔH 2 +B 1 2 ) 1/2 =B 1 sec α, ΔH is the resonance offset of the nuclear spins, and B 1 is the Rf field of a spin-lock pulse, said Rf pulse is controlled such that: B.sub.1 =v A sin 2πνt and ΔH=A(cos 2πνt+s), where S=S/A, where S is the frequency offset of a nucleus from the center of the spectrum, and where v allows for variation of B 1 throughout the sample.

Claim 23

A method of obtaining a nuclear magnetic resonance signal from a sample using a radio frequency irradiation coil which provides an inhomogeneous radio frequency magnetic field, the method comprising causing the coil to apply a radio frequency pulse to the sample in the presence of an external magnetic field, performing an adiabatic passage, and obtaining the resultant NMR signal, said adiabatic passage such that the effective field B experienced by nuclear spins within the sample is changed such that |dα/dt|<B tan α=ΔH/B 1 and B=(ΔH 2 +B 1 2 ) 1/2 =B 1 sec α, ΔH is the resonance offset of the nuclear spins, and B 1 is the Rf field of a spin-lock pulse, said Rf pulse is controlled such that: B.sub.1 =v A sin 2πνt and ΔH=A(cos 2πνt+s), where s=S/A, where S is the frequency offset of a nucleus from the center of the spectrum, and where v allows for variation of B 1 throughout the sample.

Claim 24

A method of obtaining a nuclear magnetic resonance signal from a sample using a radio frequency irradiation coil which provides an inhomogeneous radio frequency magnetic field, the method comprising causing the coil to apply a radio frequency pulse to the sample in the presence of an external magnetic field, performing an adiabatic passage, and obtaining the resultant NMR signal, said adiabatic passage such that the effective field B experienced by nuclear spins within the sample is changed such that |dα/dt|<B tan α=ΔH/B 1 and B=(ΔH 2 +B 1 2 ) 1/2 =B 1 sec α, ΔH is the resonance offset of the nuclear spins, and B 1 is the Rf field of a spin-lock pulse, said Rf pulse is controlled such that: B.sub.1 =v A sin 2πνt and ΔH=A(cos 2πνt+s), where s=S/A, where S is the frequency offset of a nucleus from the center of the spectrum, and where v allows for variation of B 1 throughout the sample.

Claim 25

The method of achieving substantially spatially uniform excitation of a sample comprising magnetic resonators, from a spatially inhomogeneous Rf field, comprising the steps of: applying a static magnetic polarizing field to said sample along a first axis, generating an Rf magnetic field principally directed along axes other than said first axis, whereby said magnetic resonators experience an effective magnetic field at an angle α to said polarizing field, to align said magnetic resonators with said effective magnetic field, concurrently modulating the amplitude and frequency of said Rf field to expose said sample to Rf irradiation for a discrete interval while (i) maintaining said effective field at a substantially constant magnitude over said interval, (ii) rotating said effective field at a substantially constant rate dα/dt over said interval, (iii) limiting said rate dα/dt to a magnitude small in comparison with the product of the government ratio with said effective field, and (iv) continuing to substantially maintain alignment of said magnetic resonators with said effective magnetic field over said interval.

Claim 26

The method of achieving substantially spatially uniform excitation of a sample comprising magnetic resonators, from a spatially inhomogeneous Rf field, comprising the steps of: applying a static magnetic polarizing field to said sample along a first axis, generating an Rf magnetic field principally directed along axes other than said first axis, whereby said magnetic resonators experience an effective magnetic field at an angle α to said polarizing field, to align said magnetic resonators with said effective magnetic field, concurrently modulating the amplitude and frequency of said Rf field to expose said sample to Rf irradiation for a discrete interval while (i) maintaining said effective field at a substantially constant magnitude over said interval, (ii) rotating said effective field at a substantially constant rate dα/dt over said interval, (iii) limiting said rate dα/dt to a magnitude small in comparison with the product of the government ratio with said effective field, and (iv) continuing to substantially maintain alignment of said magnetic resonators with said effective magnetic field over said interval.

Claim 29

A method of obtaining a nuclear magnetic resonance signal from a sample, the method comprising applying a radio frequency magnetic field pulse to the sample in the presence of an external magnetic field, wherein the Rf pulse is controlled such that: B.sub.1 =V A sin 2πνt and ΔH=A(cos 2πνt+s), or B.sub.1 =v A cos 2πνt and ΔH=A(sin 2πνt+s), where s=S/A, where S is the frequency offset of a nucleus from the centre of the spectrum, and where v allows for variation of B 1 throughout the sample, ΔH is the resonance offset of the nuclear spins, and B 1 is the Rf field of a spin-lock pulse.

Claim 30

A method of obtaining a nuclear magnetic resonance signal from a sample, the method comprising applying a radio frequency magnetic field pulse to the sample in the presence of an external magnetic field, wherein the Rf pulse is controlled such that: B.sub.1 =V A sin 2πνt and ΔH=A(cos 2πνt+s), or B.sub.1 =v A cos 2πνt and ΔH=A(sin 2πνt+s), where s=S/A, where S is the frequency offset of a nucleus from the centre of the spectrum, and where v allows for variation of B 1 throughout the sample, ΔH is the resonance offset of the nuclear spins, and B 1 is the Rf field of a spin-lock pulse.