Method for slice selection in an NMR MAS solids imaging system
AssigneeBruker Instruments, Inc.
InventorDavid G. Cory
Life of this patent
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Abstract
A multiple-pulse RF pulse sequence applied in the presence of an oscillating magnetic field gradient enables slice selection in a magic angle spinning nuclear magnetic resonance solids imaging system. Slice selectivity is produced by a series of RF pulses, some of which introduce a nutation that coherently adds for only a selected slice plane of the sample and averages to zero in other areas and some of which average certain gradient-induced modulations so that only those object areas in the selected slice contribute to the output. The pulse train is applied in a manner synchronous with rotor rotation so that rotation induced modulations average to zero over one or more rotor rotation periods.
Claims24
In an NMR magicangle-spinning solids:imaging system in which an object is placed in a main static magnetic field having a field direction and physically rotated with a predetermined rotation period about an axis positioned at an angle of 54.degree. 44' to said main magnetic field, at least one magnetic field having a field gradient perpendicular to said rotation axis is applied to said object and NMR induced magnetization is detected in a direction transverse to the main static magnetic field direction, a method for slice selection comprising the steps of:
- A. applying to said object a slice selection magnetic field gradient having a direction parallel to said rotation axis, said slice selection magnetic field gradient periodically reversing in direction with a period equal to twice said rotation period;
- and
- B. applying a periodic sequence of radio frequency pulses to said object, said sequence having a period equal to a multiple of said rotation period and each of the pulses in said sequence comprising an RF pulse applied in the X direction and an RF pulse applied alternately in the Y and Y directions, where the X and Y directions are perpendicular to the main magnetic field direction, an X RF pulse has a relative phase shift of 90.degree. with respect to a Y RF pulse and a -Y RF pulse has a relative phase shift of 180.degree. with respect to an Y pulse
A method for generating an image from a preselected portion of a solid object in an NMR magic angle spinning solids imaging system comprising the steps of:
- A. placing said object in a main static magnetic field having a field direction;
- B. physically rotating said object with a predetermined rotation period about an axis positioned at an angle of 54.degree. 44' to said main magnetic field;
- C. applying to said object at least one magnetic field having a field gradient perpendicular to said rotation axis;
- D. applying to said object a slice selection magnetic field gradient having a direction parallel to said rotation axis, said slice selection magnetic field gradient periodically reversing in direction with a period equal to twice said rotation period;
- E. applying a periodic sequence of radio-frequency pulses to said object, said sequence having a period equal to a multiple of said rotation period and each of the pulses in said sequence comprising an RF pulse applied in the X direction and an RF pulse applied alternately in the Y and -Y directions, where the X and Y directions are perpendicular to the main magnetic field direction, an X RF pulse has a relative phase shift of 90.degree. with respect to a Y RF pulse and a -Y RF pulse has a relative phase shift of 180.degree. with respect to an Y pulse;
- and
- F. detecting the NMR induced magnetization in a direction transverse to the main static magnetic field direction.
A method for generating an image from a preselected wherein step E comprises the steps of:
- E3. applying a periodic sequence of radio-frequency pulses to said object, said sequence having .epsilon. pulses applied periodically with a period equal to a multiple of twice said rotation period.
A method for generating an image from a preselected portion of a solid object in an NMR magic angle spinning solids imaging system comprising the steps of:
- A. placing said object in a main static magnetic field having a field direction;
- B. physically rotating said object with a predetermined rotation period about an axis positioned at an angle of 54.degree. 44' to said main magnetic field;
- C. applying to said object a first ma field having a first field direction and a first linear field gradient perpendicular to said rotation axis and rotating around said rotation axis in synchronism with said object;
- D. applying to said object a second magnetic field having a field gradient perpendicular to said rotation axis and a second linear field gradient orthogonal to said first magnetic field gradient, said second field rotating around said rotation axis in synchronism with said object.
- E. applying to said object a linear slice selection magnetic field gradient having a direction parallel to said rotation axis, said slice selection magnetic field gradient periodically reversing in direction with a period equal to twice said rotation period;
- F. applying a periodic sequence of radio frequency pulses to said object, said sequence having a period equal to a multiple of said rotation period and comprising a first pulse alternating with a second pulse, said first pulse comprising an .pi. pulse in the X direction followed substantially immediately by an .epsilon. pulse in the Y direction and said second pulse comprising an .pi. pulse in the X direction followed substantially immediately by an .epsilon. pulse in the Y direction, where the X and Y directions are perpendicular to the main magnetic field direction, an X RF pulse has a relative phase shift of 90.degree. with respect to a Y RF pulse and a -Y RF pulse has a relative phase shift of 180.degree. with respect to an Y pulse;
- and
- G. detecting the NMR-induced magnetization in a direction transverse to the main static magnetic field direction.
Dependencies are inferred from the claim text.