US 5,853,365 AGranted

Magnetic resonance imaging using pulse sequence including trapezoidal-wave gradient

AssigneeKabushiki Kaisha Toshiba

InventorHitoshi Yamagata

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Abstract

A method to null a phase relevant to a high-order moment and minimize an echo time TE when a GMN or flow-encoding gradient pulse is employed. The first to n-th trapezoidal-wave pulses of which polarities are alternately mutually opposite are applied as a gradient pulse. The amplitude g and pulse duration t of the first trapezoidal-wave pulse, and the slope k of pulses of the first trapezoidal-wave pulse are given as initial values. Parameters including a plurality of known pulse duration coefficients b.sub.1, b.sub.2, etc. determining pulse durations b.sub.1.t, b.sub.2.t, etc. of the first to n-th trapezoidal-wave pulses, and unknown magnetic field gradient strength coefficients a.sub.1, a.sub.2, etc. determining amplitudes a.sub.1.g, a.sub.2.g, etc. of the second and subsequent trapezoidal-wave pulses are given. Expressions concerning phases of nuclear spins producing an MR signal are solved analytically so that the values of terms of phases relevant to moments in the expressions can be controlled to be desired values or nulled according to the purpose of use of the gradient pulse. A combination of the coefficients b.sub.1, b.sub.2, etc. satisfying the results of the analysis, in which the coefficient b.sub.3 for a pulse interval defining the pulse spacing of the n-th trapezoidal-wave pulse has the smallest value, is selected.

Claims20

Dependent claims

A method of magnetic resonance imaging by which an object is scanned using a pulse sequence including a gradient pulse for controlling moments of nuclear spins in motion in the object, comprising the steps of:

analytically preparing the pulse sequence in advance;
and
performing a scan on the object using the pulse sequence,
wherein the analytical preparing step further includes the steps of:
providing, as said gradient pulse, a pulse train having three or more trapezoidal-wave pulses of which polarities are alternately inverted,
wherein both an amplitude and a pulse duration of a first trapezoidal-wave pulse residing first in the pulse train and a rise time rate of each of the three or more trapezoidal-wave pulses are given as initial values, a plurality of pulse duration coefficients which determine pulse spacings of trapezoidal-wave pulses other than the first trapezoidal-wave pulse in the pulse train are given as known values, and magnetic field gradient strength coefficients which determine amplitudes of the of the trapezoidal-wave pulses other than the first trapezoidal-wave pulse in the pulse train are given as unknown values;
solving for the unknown magnetic field gradient strength coefficients from expressions concerning a plurality of different dimensions of moments of phase shifts caused by the nuclear spins producing a magnetic resonance signal so that the plurality of different dimensions of the moments of phase shifts are moment by moment at least one of 1) controlled to desired values other than zero and 2) compensated to null values according to a purpose of use of said gradient pulse, the expressions being reflected by both the initial values and the magnetic field gradient strength coefficients;
and
selecting one combination from a plurality of combinations of pulse duration coefficients satisfying results performed in the solving step, the one combination determining a shortest pulse train interval.

6 more elements

A system for magnetic resonance imaging in which an object is scanned using a pulse sequence including a gradient pulse for controlling moments of nuclear spins in motion in the object, comprising:

means for setting the pulse sequence by analytical calculation
as said gradient pulse, to include a pulse train having more than two trapezoidal-wave pulses of which polarities are alternately inverted,
wherein both an amplitude and a pulse duration of a first trapezoidal-wave pulse residing first in the pulse train and a rise time rate of each of the more than two trapezoidal-wave pulses are given as initial values, a plurality of pulse duration coefficients which determine pulse spacings of trapezoidal-wave pulses other than the first trapezoidal-wave pulse in the pulse train are given as known values, and magnetic field gradient strength coefficients which determine amplitudes of the trapezoidal-wave pulses other than the first trapezoidal-wave pulse in the pulse train are given as unknown values,
wherein expressions concerning a plurality of different dimensions of moments of phase shifts caused by nuclear spins producing a magnetic resonance signal are solved for the unknown magnetic field gradient strength coefficients so that the plurality of different dimensions of the moments of phase shift are moment by moment at least one of 1) controlled to desired values other than zero and 2) compensated to null values according to a purpose of use of said gradient pulse, the expressions being reflected by both the initial values and the magnetic field gradient strength coefficients, and
wherein one combination is selected from a plurality of combinations of pulse duration coefficients satisfying a solution of said expressions concerning said plurality of different dimensions of moments of phase shifts, the one combination determining a shortest pulse train interval;
means for performing a scan on the object to acquire the magnetic resonance signal using the pulse sequence set by said means for setting;
and
means for producing a magnetic resonance image from the acquired magnetic resonance signal.

5 more elements

Dependencies are inferred from the claim text.