Imaging systems
AssigneeEMI Limited
InventorPeter E. Walters
Life of this patent
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Abstract
In a nuclear magnetic resonance imaging apparatus it has been proposed to excite resonance preferentially in a cross-sectional slice of a patient's body by applying a field gradient pulse in conjunction with a pulse of RF. It has been found that the shape of the RF pulse envelope can be chosen to reduce excitation outside the chosen slice. It is proposed that the RF envelope should be a unidirectional pulse of which both the rising and falling parts are monotonic curves lying between limits given by sin.sup.3 t and sin.sup.10 t curves, preferably sin.sup.5 t. An acceptable curve may fall below sin.sup.10 t in the skirts but should not change sign.
Claims15
An apparatus for examining a body by means of nuclear magnetic resonance, the apparatus including:
- means for applying to the body a steady magnetic field along an axis therein;
- means for applying a pulsed gradient field which, in conjunction with the steady field, gives a predetermined field in a cross-sectional slice of the body;
- means for applying a pulsed periodic magnetic field at the Larmor frequency for the field in said slice to cause resonance preferentially therein, the pulse envelope of said periodic field having a rising part and a falling part each of which conforms to a monotonic curve lying substantially between limits defined by a curve defined by amplitude=a sin.sup.3 bt and by a curve defined by amplitude=a sin.sup.10 bt, where b defines a duration substantially equal to the gradient field pulse;
- means for detecting the resonance signal resulting from said resonance;
- and means for analysing said signal.
An apparatus for examining a body by means of nuclear magnetic resonance, the apparatus including:
- means for applying to the body a steady magnetic field along an axis therein;
- means for applying a pulsed gradient field which, in conjunction with the steady field, gives a predetermined field in a cross-sectional slice of the body;
- means for applying a pulsed periodic magnetic field at the Larmor frequency for the field in said slice to cause resonance preferentially therein;
- means for detecting the resonance signal resulting from said resonance;
- and means for analysing said signal;
- wherein the said periodic field has a pulse envelope of shape lying between extremes defined by amplitude=a sin.sup.3 bt and amplitude=a sin.sup.10 bt where b is set to define the duration and a is set to adjust the peak amplitude to give a desired total field integral for the pulse.
An apparatus for examining a body by means of nuclear magnetic resonance, the apparatus including:
- means for applying to the body a steady magnetic field along an axis therein;
- means for applying a pulsed gradient field which, in conjunction with the steady field, gives a predetermined field in a cross-sectional slice of the body;
- means for applying a pulsed periodic magnetic field at the Larmor frequency for the field in said slice to cause resonance preferentially therein;
- means for detecting the resonance signal resulting from said resonance;
- and means for analysing said signal;
- wherein the said periodic field has a pulse envelope which is of single sign and has rising and falling half heights an opposite sides of the centre of the gradient field pulse and occuring within limits of 17% and 32% of the half height width of the gradient field pulse from said centre.
A method of examining a body by nuclear magnetic resonance, the method including:
- applying to the body a magnetic field including a pulsed field gradient along an axis in the body to provide a predetermined field in a cross-sectional slice perpendicular to said axis;
- applying a pulsed periodic magnetic field at the Larmor frequency for said predetermined field to preferentially cause resonance in the slice;
- and sensing the resulting resonance signed for subsequent analysis;
- wherein the periodic field envelope is a single unidirectional pulse lying substantially inside the curve defined by amplitude=a sin.sup.3 bt, where b defines a direction substantially that of the gradient pulse and a is chosen to give a desired total field integral for the pulse.
A method of examining a body by nuclear magnetic resonance, the method including;
- applying the body a magnetic field including a pulsed field gradient along an axis in the body to provide a predetermined field in a cross-sectional slice perpendicular to said axis;
- applying a pulsed periodic magnetic field the Larmor frequency for said predetermined field to preferfentially cause resonance in the slice;
- and sensing the resulting resonance signal for subsequent analysis;
- wherein the periodic field envelope is a single unidirectional pulse having rising and falling half heights within 32% of the half height width of the field gradient pulse from the centre of said gradient pulse.
Dependencies are inferred from the claim text.