Method and apparatus for obtaining nuclear magnetic resonance spectra

A method of obtaining a localized 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 first plurality of radiofrequency pulse sequences, each of said first plurality of pulse sequences including an excitation pulse and at least two localization pulses, wherein each localization pulse is of the form A[.+-.x], or A[.+-.x,.+-.y], or wherein "A" indicates the magnitude of the pulse, the notation [.+-.x] indicates that the corresponding pulse occurs in one half of the corresponding pulse sequences with an initial phase and in the remaining pulse sequences with its phase shifted by 180.degree. with respect to the initial phase, and wherein the notation [.+-.x,.+-.y] indicates that the corresponding pulse occurs within an initial phase in a first quarter of the pulse sequences, with a phase shifted by 90.degree. from its initial phase in a second quarter of the pulse sequences, with a phase shifted by 180.degree. from its initial phase in a third quarter of the pulse sequences and with a phase shifted by 270.degree. from its initial phase in a fourth quarter of the pulse sequences, the arrangement being such that a pulse sequence exists with each permutation of permitted phase possibilities for each of said localization pulses with each permitted phase possibility for each of the other said localization pulses;
• applying to the sample a second plurality sequences, the second differing from the first plurality by the omission in the sequence of the second plurality of at least one of said localization pulses;
• acquiring an N.M.R. signal after each pulse sequence;
• and
• combining the N.M.R. signals obtained within each of said first and second pluralities of sequences, and further combining N.M.R. signals obtained from said first and second pluralities of sequences to produce a localized N.M.R. signal from selected regions of the sample.

A method of obtaining a localized nuclear magnetic resonance signal from a sample using a radiofrequency irradiation coil which provides an inhomogeneous radiofrequency field, comprising:

• applying to the sample of a plurality radiofrequency pulse sequences, each pulse sequence including at least one localization pulse, and a plurality of excitation pulses, the nth excitation pulse having a magnitude of (2n-1) times that of the first excitation pulse;
• acquiring an N.M.R. signal after each pulse sequence;
• and
• combining the N.M.R. signals obtained to produce a localized N.M.R. signal from selected regions of the sample.

A method of obtaining a localized nuclear magnetic resonance signal from a sample using a radiofrequency irradiation coil which provides an inhomogeneous radiofrequency field, comprising:

• applying to the sample n pluralities of radiofrequency pulse sequences, each pulse sequence including an excitation pulse and at least one localization pulse, the phase of said localization pulse being shifted by 180.degree. in predetermined sequences of the said plurality;
• wherein the magnitude of the excitation pulse in each sequence of the nth said plurality is (2n-1) times the magnitude of the excitation pulse of a first plurality;
• acquiring an N.M.R. signal after each pulse sequence;
• and
• combining the N.M.R. signals obtained to produce a localized N.M.R. signal from selected regions of the sample.

Apparatus for obtaining an N.M.R. spectrum from a sample, comprising

• means for generating a static magnetic field;
• support means for supporting the sample in the static magnetic field;
• means capable of generating a plurality of radiofrequency pulse sequences in one of the following manners:
• (A) each pulse sequence includes at least one excitation pulse, and at least three localization pulses, wherein each localization pulse is of the form A[.+-.x], or A[.+-.x,.+-.y], wherein "A" indicates the magnitude of the pulse, the notation [.+-.x] indicates that the corresponding pulse occurs in one half of the corresponding pulse sequences with an initial phase and in the remaining pulse sequences with its phase shifted by 90.degree. with respect to the initial phase, and wherein the notation [.+-.x,.+-.y] indicates that the corresponding pulse occurs within an initial phase in a first quarter of the pulse sequences, with a phase shifted by 90.degree. from its initial phase in a second quarter of the pulse sequences, with a phase shifted by 180.degree. from its initial phase in a third quarter of the pulse sequences and with a phase shifted by 270.degree. from its initial phase in a fourth quarter of the pulse sequences, the arrangement being such that a pulse sequence exists with each permutation of permitted phase possibilities for each of the said localization pulses with each permitted phase possibility for each of the other said localization pulses, characterized in that the said pulse sequences contain at least two of the said excitation pulses of the form A[.+-.x];
• (B) first and second pluralities of sequences are applied, each pulse sequence in said first plurality includes an excitation pulse and at least two localization pulses, wherein each localization pulse is of the form A[.+-.x], A[.+-.x,.+-.y], wherein "A" indicates the magnitude of the pulse, the notation [.+-.x] indicates that the corresponding pulse occurs in one half of the corresponding pulse sequences with an initial phase and in the remaining pulse sequences with its phase shifted by 180.degree. with respect to the initial phase, and wherein the notation [.+-.x,.+-.y] indicates that the corresponding pulse occurs within an initial phase in a first quarter of the pulse sequences, with a phase shifted by 90.degree. from its initial phase in a second quarter of the pulse sequences, with a phase shifted by 180.degree. from its initial phase in a third quarter of the pulse sequences and with a phase shifted by 270.degree. from its initial phase in a fourth quarter of the pulse sequences, the arrangement being such that a pulse sequence exists with each permutation of permitted phase possibilities for each pulse of the said localization pulses with each permitted phase possibility for each other said localization pulse, applying to the sample a second plurality of sequences, the second differing from the first plurality by the omission in the sequence of the second plurality of at least one of said localization pulses;
• and, (C) each pulse sequence includes at least one localization pulse, and a plurality of excitation pulses, the nth excitation pulse having a magnitude of (2n-1) times that of the first excitation pulse;
• irradiation means including a radiofrequency irradiation coil adjacent to the sample support means, having an inhomogeneous radiofrequency field in the intended region of the sample;
• means for applying the plurality and pluralities of pulse sequences to the coil;
• and
• means for detecting an N.M.R. signal from a sample supported by the sample support means;
• means for (1) combining the N.M.R. signals obtained from said plurality of sequences according to procedures (A) and (C) above, and for (2) combining the N.M.R. signals obtained from procedure (C) above within each of said first and second pluralities of sequences, and further combining N.M.R. signals obtained from said first and second pluralities of sequences, to produce a localized N.M.R. signal from selected regions of the sample.