Surgery – Diagnostic testing – Detecting nuclear – electromagnetic – or ultrasonic radiation
Patent
1997-03-21
1998-12-29
Smith, Ruth S.
Surgery
Diagnostic testing
Detecting nuclear, electromagnetic, or ultrasonic radiation
600419, 324306, 324309, A61B 5055
Patent
active
058533656
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.
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J. L. Duerk, et al., "Analysis of Imaging Axes Significance in Motion Artifact Suppression Technique (MAST): MRI of Turbulent Flow and Motion", Magn. Reson. Imag., vol. 7, pp. 251-263, 1989.
P. M. Pattany, et al., "Motion Artifact Suppression Technique (MAST) for MR Imaging", J. of Comput. Assist. Tomogr., vol. 11, (3), pp. 369-377, 1987.
H. Yamagata, "Optimized Gradient Pulses for MR Quantitative Flow Imaging and Angiography", RSNA, vol. 173 (P), p. 162, 1989.
Kabushiki Kaisha Toshiba
Smith Ruth S.
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