Frequency selective pulse
AssigneeGE Medical Systems SA
InventorsDaniel Rosenfeld, Shimon L. Panfil, Yuval Zur
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Abstract
A method of NMR (nuclear magnetic resonance) excitation of a sample having a magnetic moment, including, applying a longitudinal magnetic field to the sample; and changing the magnetic moment in a substantially continuous manner by moving an effective magnetic-field vector ωe more than 90°, wherein for all portions of the sample in which the moment is changed, the angular velocity of the effective field vector at at least one angle, 90°+α, is different from the angular velocity at 90°−α.
Claims27
A method of NMR (nuclear magnetic resonance) excitation of a sample having a magnetic moment comprising:
- applying a longitudinal magnetic field to the sample;
- inverting the magnetization of at least a portion of the sample, using an FM pulse having a duration, wherein the FM pulse has asymmetrical characteristics, wherein a resulting magnetization profile MZ of the sample has an asymmetric characteristic, comprising at least a narrow transition and a broad transition, and wherein the magnetization profile has the formula:
- M z = sin h π r sin h π v + cos 2 π q cos h π r cos h π v wherein r = d - ω 0 b v = ( c + d ) - ω 0 ( a + b ) q = 1 2 Ω 0 2 - ( c - ω 0 a ) 2
- wherein a, b, c, d and Ω0 are parameters having real values, ω0 is the Larmor frequency and wherein a≠0, and (c≠0 or d≠0), wherein if q is imaginary, M z = sin h π r sin h π v + cos h2 π [LeftBracketingBar] q [RightBracketingBar] cos h π r cos h π v
A method of NMR (nuclear magnetic resonance) of a sample having a magnetic moment comprising:
- applying a longitudinal magnetic field to the sample;
- inverting the magnetization of at least a portion of the sample, using an FM pulse having a duration, wherein the FM pulse has asymmetrical characteristics, and changing the magnetic moment in a substantially continuous manner by moving an effective magnetic field vector more than 90°+α, wherein for all portions of the sample in which the moment is changed, the angular velocity of the effective field vector at at least one angle, 90°+α, is different from the angular velocity at 90°−α;
- wherein moving the magnetic-field vector comprises applying an FM pulse and wherein vector ωe has components ωx, ωy and ωz and wherein said changing comprises changing according to the following formula:
- ω x = ω 1 = Ω 0 ( z ( 1 - z ) ) 0.5 / ( az + b ) ω y = 0 ω z = ω - ω o = cz + d az + b - ω 0
- wherein, the frame of reference for the formula is a frame rotating at the instantaneous frequency of the FM pulse and wherein z is selected from the range 0 to 1 and wherein a time variable t is given by:
- t = 1 n z b ( 1 - z ) a + b
A method of NMR (nuclear magnetic resonance) excitation of a sample having a magnetic moment, comprising:
- applying a longitudinal magnetic field to the sample;
- changing the magnetic moment in a continuous manner using an FM pulse;
- and
- varying an effective magnetic-field vector ωe having components ωx, ωy and ωz and associated with the FM pulse, according to the following formula:
- ω x = ω 1 = Ω 0 z ( 1 - z ) az + b ω y = 0 ω z = ω - ω 0 = cz + d az + b - ω 0
- wherein, the frame of reference for the formula is a frame rotating at the instantaneous frequency of the FM pulse and wherein z is selected from the range 0 to 1 and wherein a time variable t is given by:
- t = ln z b ( 1 - z ) a + b
- wherein a, b, c, d and Ω0 are parameters having real values and wherein a≠0, and (c≠0 or d≠0).
Dependencies are inferred from the claim text.