Imaging systems
AssigneeEMI Limited
InventorsColin G. Harrison, Ian R. Young
Life of this patent
Estimating the term…
Abstract
Nuclear magnetic resonance (NMR) apparatuses have been proposed to examine slices or volumes of bodies, perhaps patients for medical purposes, by exciting resonance and detecting the resonance signals. In an NMR apparatus an G.sub.R field gradient, for selecting lines within a slice or volume, is formed of Gx and Gy components. These should match exactly in shape if not in magnitude. In practice this is difficult to achieve and it is proposed to monitor these fields and derive error signals for their deviation from each other or from a standard. The error signals are used to reduce the deviations so that continuous adjustment of the fields is provided.
Claims16
A nuclear magnetic resonance apparatus, for examining at least one slice of a body, the apparatus including means for applying magnetic fields to the body to cause resonance preferentially in said slice, means for applying a pulsed magnetic field having a gradient across said at least one slice to produce phase dispersion in said resonance, and means for sensing, during the application of said gradient field, the resonance signal induced, wherein means are provided to cause the gradient field when in use to have a gradient in different directions in the slice at different times by varying proportions of two component magnetic fields with orthogonal gradients, the apparatus further including means for sensing the magnetic fields at a plurality of positions in the plane of the slice, means for deriving therefrom error signals indicative of differences between the fields measured in two orthogonal directions and those fields required to provide the gradient magnetic field of a desired magnitude in a desired direction, and means for using the error signals to adjust the component fields to their required values.
A medical nuclear magnetic resonance apparatus for examining at least one cross-sectional region of the body of a patient the apparatus including means for applying to the body a steady magnetic field along an axis therein, means for applying a gradient field which, in conjunction with said steady field, gives a predetermined field in said region, means for applying a pulsed periodic magnetic field at the Larmor frequency for the field in said region to cause resonance therein, means for applying a further pulsed magnetic field having a gradient across the region to cause frequency dispersion therein and means for sensing the resonance signal resulting from the region, wherein the means for applying the further magnetic field includes means for causing the further field when in use to have a gradient in different directions in the region at different times by applying varying proportions of component magnetic fields with gradients in substantially orthogonal directions, the apparatus further including means for sensing the magnetic fields at a plurality of positions in the region, means for deriving therefrom error signals indicative of differences between the fields measured in the orthogonal directions and those fields required to provide the further magnetic field of a desired magnitude in the desired direction, and means for using the error signals to adjust the component fields to their required values.
A method of examining a body by gyromagnetic resonance, in particular nuclear magnetic resonance, including the steps of:
- applying magnetic fields to induce resonance preferentially in at least a slice of the body;
- applying magnetic fields, including a pulsed field having a gradient across the slice in one direction, to cause phase dispersion of said resonance, wherein the pulsed field is caused to have a gradient in different directions in the slice at different times by varying proportions of two component magnetic fields which have field gradients orthogonal to each other and which, together, form said pulsed field;
- sensing the magnetic fields at a plurality of positions in the plane of the slice;
- deriving therefrom error signals indicative of differences between the fields measured in two orthogonal directions and those fields required to provide the pulsed magnetic field of the desired magnitude with its gradient in a desired direction;
- using the error signals to bring the component fields closer to their required values;
- and sensing the resonance signal resulting from the slice.
A method of examining a cross-sectional region of the body of a patient by gyromagnetic resonance, in particular nuclear magnetic resonance, the method including the steps of:
- applying to the body a steady magnetic field along an axis therein;
- applying a gradient field which, in conjunction with said steady field gives a predetermined field in said region;
- applying a periodic magnetic field at the Larmor frequency for the field in said region to cause resonance preferentially therein;
- applying a further magnetic field having a gradient across the region to cause frequency dispersion in said resonance, wherein the further magnetic field is caused to have gradient in different directions in the slice at different times by varying the proportions of component magnetic fields which have field gradients in substantially orthogonal directions and which, together, form said further field;
- sensing the magnetic fields at a plurality of positions in the region;
- deriving therefrom error signals indicative of differences between the fields measured in the orthogonal directions and those fields required to provide the further magnetic field of a desired magnitude in a desired direction;
- using the error signals to bring the component fields closer to their required values;
- and sensing the resonance signal resulting from the region.
A medical nuclear magnetic resonance apparatus for examining at least one substantially cross-sectional region of the body of a patient, the apparatus including means for applying to the body magnetic fields which cause resonance preferentially in said region, means for applying to the body a plurality of further magnetic fields which have gradients in different directions in the region, means for sensing the resonance signal resulting from the region, which signal includes spatially distinguishable information by virtue of said field gradients, and processing said resonance signal to recover the spatial information and provide an image of said region, wherein the apparatus further includes means for sensing the magnetic fields at a plurality of positions in the region, means for deriving therefrom error signals indicative of differences between the fields measured and those fields required to provide the field gradients of desired magnitudes in desired directions, and means for using the error signals to adjust the magnetic fields to their required values.
A method of examining a cross-sectional region of the body of a patient by nuclear magnetic resonance, the method including the steps of:
- applying to the body magnetic fields which induce resonance preferentially in said region;
- applying a plurality of further magnetic fields which have gradients in different directions in the region;
- sensing the resonance signal resulting from the region, the resonance signal including spatially distinguishable information as a result of said field gradients;
- and processing the resonance signal to recover the spatial information and provide an image of said region;
- the method further including:
- sensing the magnetic fields at a plurality of positions in the region;
- deriving therefrom error signals indicative of differences between the fields measured and those fields required to provide the magnetic field gradients of desired magnitudes and in desired directions;
- and using the error signals to adjust the field gradients to be closer to the desired values.
Dependencies are inferred from the claim text.