Imaging systems

A method of examining a body by gyromagnetic resonance the method including the steps of:

• applying a gradient field which, in conjunction with said steady field gives a predetermined field in said slice, applying a periodic magnetic field at the Larmor frequency for the slice to cause resonance therein;
• applying a further magnetic field having a gradient across the slice in one direction and a second further magnetic field having a gradient across the slice in the same direction but of opposite sense to the first further field;
• and sensing the resonance signal resulting from the slice during the further fields wherein the method further includes the step of applying a correction magnetic field also having a gradient across the slice in said direction and being such that the total algebraic field integral with respect to time over the two further fields and the correction field is less than the total field integral for the two further fields.

A nuclear magnetic resonance apparatus for examining at least one cross-sectional region of a body, the apparatus including means for applying to the body a steady magnetic field along an axis therein, means for applying a second magnetic field having a gradient which, in conjunction with said steady field, gives a predetermined field in said region, means for applying a periodic magnetic field at the Larmor frequency for said region to cause resonance therein, means for applying a first further magnetic field having a gradient across the slice in a chosen direction, means for applying a second further magnetic field also having a gradient across the slice and substantially opposing the first further magnetic field, means for sensing the resonance signal resulting from the region during the said further magnetic fields and means for applying a third further magnetic field having a gradient in the region, being substantially equal and opposite to any difference between the first and second further fields to reduce the total magnetic field integral over the three further magnetic fields to substantially zero.

A nuclear magnetic resonance apparatus, for examining at least one region of a body, the apparatus including means for applying magnetic fields to cause resonance preferentially in said region, means for applying a magnetic field having a gradient in said region to cause phase dispersion in said resonance, means for applying a second magnetic field having a gradient in said region but of opposite sense to the first gradient field to oppose said phase dispersion, means for sensing the resonance signal resulting from the region during said gradient fields for processing to provide nuclear magnetic resonance information for said region, and means for applying a third magnetic field having a gradient in said region the sense direction and magnitude of said third gradient field being such as to further reduce any phase dispersion in said resonance outstanding after the application of the first and second gradient fields.

A nuclear magnetic resonance apparatus, for examining a region of a body, the apparatus including means for applying magnetic fields to cause resonance preferentially in said region, means for applying component magnetic fields, one of which may be of zero magnitude, having gradients in orthogonal directions in said region to provide a first magnetic field having a gradient in a chosen direction to produce phase dispersions in said resonance insaid direction, means for applying further component magnetic fields, one of which may be of zero magnitude, having gradients in orthogonal directions in said region to provide a second magnetic field having a gradient in said region in a direction and of a magnitude to oppose the first gradient field to tend to reduce said phase dispersion, means for sensing the resonance signal resulting from the region during said gradient fields for processing to provide nuclear magnetic resonance information for said region, and means for applying yet further component magnetic fields one of which may be of zero magnitude, having gradients in orthogonal directions in said region to provide a third magnetic field having a gradient in said region, of a magnitude and direction to tend to reduce phase dispersion in said resonance outstanding after the application of the first and second gradient fields.

A nuclear magnetic resonance apparatus, for examining a region of a body, the apparatus including means for applying magnetic fields to cause resonance preferentially in said region, means for applying a first magnetic field having a gradient across the region in a chosen direction and a second magnetic field having a gradient across the region in substantially the same direction but of opposite sense to the first gradient field, means for sensing the resonance signal resulting from the region during the said gradient fields and means for applying a correction magnetic field also having a gradient across the region in substantially the same direction and chosen so that the total algebraic integral with respect to time of the magnetic field intensity over the three gradient fields is less than the total field integral for the first and second gradient fields.