Method and apparatus for obtaining nuclear magnetic resonance spectra

Claim 1

A method of obtaining a localised nuclear magnetic resonance signal from a sample using a radiofrequency irradiation coil which provides an inhomogeneous radiofrequency field, comprising applying to the sample a plurality of radiofrequency pulse sequences, each pulse sequence including an excitation pulse, and at least two other pulses, the pulse sequences differing only in the phase of one or more of the said other pulses, and the phases of at least two of the said other pulses being shifted by 180° in selected sequences of the said plurality, the number of sequences in the said plurality being such that a sequence exists for each possible combination of the said phase shifts for each of the said other pulses, and there being no sequences in the said plurality in which the phases of the said at least two of the said other pulses is shifted by 90°, acquiring an N.M.R. signal after each pulse sequence, and combining the N.M.R. signals obtained to produce a localised N.M.R. signal from selected regions of the sample.

Claim 2

A method of obtaining a localised nuclear magnetic resonance signal from a sample using a radiofrequency irradiation coil which provides an inhomogeneous radiofrequency field, comprising applying to the sample a plurality of radiofrequency pulse sequences, each pulse sequence including an excitation pulse, and at least two other pulses, the pulse sequences differing only in the phase of one or more of the said other pulses, and the phases of at least two of the said other pulses being shifted by 180° in selected sequences of the said plurality, the number of sequences in the said plurality being such that a sequence exists for each possible combination of the said phase shifts for each of the said other pulses, and there being no sequences in the said plurality in which the phases of the said at least two of the said other pulses is shifted by 90°, acquiring an N.M.R. signal after each pulse sequence, and combining the N.M.R. signals obtained to produce a localised N.M.R. signal from selected regions of the sample.

Claim 5

A method as claimed in any one of claims 1 to 3 wherein the plurality of radiofrequency pulse sequences is of the form 2⊖[±x] ;2⊖ [±x] ;⊖ ;2⊖[±x, ±y] ;acquire signal, 2⊖[±x];4⊖[±x];{⊖ -3⊖+5⊖};2⊖ [±x,±y];acquire signal, 2⊖[±x] ;4⊖[±x]; {⊖-3⊖+5⊖-7⊖+9⊖};2⊖[±x,±y]; acquire signal, or 4⊖[±x] ;6⊖[±x] ;8⊖ [±x] ;{⊖-3⊖+5⊖-7⊖ +9⊖};2⊖ [±x,±y] ; acquire signal wherein θ is an arbitrary pulse angle value.

Claim 6

A method as claimed in any one of claims 1 to 3 wherein the sequences of radiofrequency pulses are of the form 2⊖[±+x];2±[±x]; ⊖;2⊖[±x, ±y];acquire signal, 2⊖[±x];4⊖[±x];{⊖-3⊖+5⊖};2⊖[±x,±y];acquire signal, 2⊖[±x];4⊖[±x];{⊖-3⊖+5⊖-7⊖+9⊖};2⊖[±x,±y]; acquire signal, or 4⊖ [±x]; 6⊖[±x];8⊖[±x];{⊖-3⊖+5⊖-7⊖+9⊖};2⊖ [±x,±y]; acquire signal with the addition of at least one further pulse of the form ⊖/3[±x] or ⊖/5[±x], wherein ⊖ is an arbitrary pulse angle value.

Claim 7

A method of obtaining a localised nuclear magnetic resonance signal from a sample using a radiofrequency irradiation coil which provides an inhomogeneous radiofrequency field, which method comprises applying to the sample a plurality of radiofrequeney pulse sequences, each pulse sequence including an excitation pulse, and at least one other pulse, the pulse sequences differing only in the phase of one or more of the said at least one other pulse, and the phases of at least one of the said at least one other pulse being shifted by 180° in selected sequences of the said plurality, the number of sequences in the said plurality being such that a sequence exists for each possible combination of the said phase shifts for each said at least one other pulse, and there being no sequences in the said plurality in which the phase of the said at least one of the said at least one other pulse is shifted by 90°, applying to the sample a second plurality of pulse sequences, the second plurality differing from the first plurality by the omission in the sequences of the second plurality of the said at least one of the said at least one other pulse, acquiring an N.M.R. signal after each pulse sequence, and combining the N.M.R. signals obtained to produce a localised N.M.R signal from selected regions of the sample.

Claim 8

A method of obtaining a localised nuclear magnetic resonance signal from a sample using a radiofrequency irradiation coil which provides an inhomogeneous radiofrequency field, which method comprises applying to the sample a plurality of radiofrequeney pulse sequences, each pulse sequence including an excitation pulse, and at least one other pulse, the pulse sequences differing only in the phase of one or more of the said at least one other pulse, and the phases of at least one of the said at least one other pulse being shifted by 180° in selected sequences of the said plurality, the number of sequences in the said plurality being such that a sequence exists for each possible combination of the said phase shifts for each said at least one other pulse, and there being no sequences in the said plurality in which the phase of the said at least one of the said at least one other pulse is shifted by 90°, applying to the sample a second plurality of pulse sequences, the second plurality differing from the first plurality by the omission in the sequences of the second plurality of the said at least one of the said at least one other pulse, acquiring an N.M.R. signal after each pulse sequence, and combining the N.M.R. signals obtained to produce a localised N.M.R signal from selected regions of the sample.

Claim 12

A method as claimed in any one of the preceding claims, wherein each of the said pluralities is repeated to provide a plurality of runs, the nth run differing from the first run in that the magnitude of the excitation pulse in the nth run is (2n - 1) times the magnitude of the excitation pulse in the first run, and thereby an nth localised N.M.R. signal is produced for each of the said runs, and the n N.M.R. signals are combined to produce an overall localised N.M.R. signal.

Claim 13

A method of obtaining a localised nuclear magnetic resonance signal from a sample using a radiofrequency irradiation coil which provides an inhomogeneous radiofrequency field, comprising applying to the sample a plurality of radiofrequency excitation pulses, the nth pulse having a magnitude of (2n - 1) times that of the first pulse, acquiring an N.M.R. signal after each pulse, and combining the N.M.R. signals obtained to produce a localised N.M.R. signal from selected regions of the sample.

Claim 14

A method of obtaining a localised nuclear magnetic resonance signal from a sample using a radiofrequency irradiation coil which provides an inhomogeneous radiofrequency field, comprising applying to the sample a plurality of radiofrequency excitation pulses, the nth pulse having a magnitude of (2n - 1) times that of the first pulse, acquiring an N.M.R. signal after each pulse, and combining the N.M.R. signals obtained to produce a localised N.M.R. signal from selected regions of the sample.

Claim 15

A method of obtaining a localised nuclear magnetic resonance signal from a sample using a radiofrequency irradiation coil which provides an inhomogeneous radiofrequency field, comprising applying to the sample at least a first plurality and a second plurality of radiofrequency pulse sequences, each pulse sequence including an excitation pulse, and at least one other pulse, the pulse sequences differing only in the phase of one or more of the said at least one other pulse, and the phase of the said at least one other pulse being shifted by 180° in selected sequences of the said plurality, the number of sequences in each plurality being such that a sequence exists for each possible combination of the 180° phase shifts for each said at least one other pulse, and wherein the magnitude of the excitation pulse in each sequence of the nth said plurality is (2n - 1) times that in each sequence of the first plurality, acquiring an N.M.R. signal after each pulse sequence, and combining the N.M.R. signals obtained to produce a localised N.M.R. signal from selected regions of the sample.

Claim 16

A method of obtaining a localised nuclear magnetic resonance signal from a sample using a radiofrequency irradiation coil which provides an inhomogeneous radiofrequency field, comprising applying to the sample at least a first plurality and a second plurality of radiofrequency pulse sequences, each pulse sequence including an excitation pulse, and at least one other pulse, the pulse sequences differing only in the phase of one or more of the said at least one other pulse, and the phase of the said at least one other pulse being shifted by 180° in selected sequences of the said plurality, the number of sequences in each plurality being such that a sequence exists for each possible combination of the 180° phase shifts for each said at least one other pulse, and wherein the magnitude of the excitation pulse in each sequence of the nth said plurality is (2n - 1) times that in each sequence of the first plurality, acquiring an N.M.R. signal after each pulse sequence, and combining the N.M.R. signals obtained to produce a localised N.M.R. signal from selected regions of the sample.

Claim 17

A method as claimed in any one of the preceding claims, wherein a quadrature phase compensation scheme is employed.

Claim 18

A method as claimed in any one of the preceding claims, wherein the phase of all pulses of any sequence which requires inversion of the receiver phase is inverted, and the same receiver phase is used for all signal acquisitions.

Claim 19

A method as claimed in any one of the preceding claims, wherein a spin-echo technique or inversion-recovery T 1 measurement is carried out on the sample.

Claim 20

A method as claimed in any one of the preceding claims, wherein at least one delay is provided between two or more of the said radiofrequency pulses.

Claim 22

A method as claimed in any one of the preceding claims, wherein at least one magnetic field gradient is applied to the sample during the application of a radiofrequency pulse.

Claim 23

A method as claimed in any one of the preceding claims, wherein radiofrequency pulses are applied with a first radiofrequency coil (6) and signal acquisition is carried out using a second-radiofrequency coil (6a).

Claim 24

A method as claimed in any one of the preceding claims, wherein some radiofrequency pulses are applied with a first radiofrequency coil (6) and the remaining radiofrequency pulses are applied with one or more other radiofrequency coils.

Claim 25

A method as claimed in any one of the preceding claims, wherein one or more of the radiofrequency pulses is a complex radiofrequency pulse.