Method for reversing residual transverse magnetization due to phase-encoding magnetic field gradients
First Claim
1. A method for undoing the effect of magnetic field gradients on the residual transverse magnetization in a pulse sequence useful for producing images of a study object positioned in a homogeneous magnetic field, which pulse sequence includes a predetermined plurality of sequentially implemented views, each of said views including at least one RF excitation pulse for exciting nuclear spins in the object, one 180°
- RF pulse for generating a spin-echo signal, and at least one encoding magnetic field gradient pulse used to encode spatial information into said spin-echo signal, said method comprising the steps of;
applying said encoding magnetic field gradient pulse subsequent to the irradiation of the study object with said 180°
RF pulse, but prior to the occurrence of said spin-echo signal, said encoding magnetic field gradient pulse being applied along at least one directional axis of the study object; and
applying, following the occurrence of said spin-echo signal, a reversing magnetic field gradient pulse so as to undo the effects of said encoding magnetic field gradient pulse on any residual transverse magnitization, the amplitude of said reversing and encoding gradient pulses being selected such that the algebraic sum thereof along said one axis is equal to a constant.
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Abstract
A method for reversing residual transverse magnetization due to spatial encoding magnetic field gradient pulses, used in magnetic resonance imaging to encode spatial information, employs a reversing gradient pulse applied in the same direction as the encoding gradient pulse following the observation of the spin-echo signal. The encoding gradient pulse is applied following the 180° RF pulse to avoid the effects of imperfections associated therewith. In one embodiment, the amplitudes of the encoding and reversing gradient pulses are selected to be approximately the negatives of each other so as to substantially cancel the residual magnetization. In another embodiment, the amplitude of the reversing gradient pulse is selected such that the algebraic sum thereof with the corresponding amplitude of the encoding gradient pulse is a constant. In this case, the residual magnetization is not necessarily cancelled, but rather, is left in the same state after each view of the pulse sequence. The method is applicable to multiple-echo and driven equilibrium pulse sequences.
37 Citations
10 Claims
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1. A method for undoing the effect of magnetic field gradients on the residual transverse magnetization in a pulse sequence useful for producing images of a study object positioned in a homogeneous magnetic field, which pulse sequence includes a predetermined plurality of sequentially implemented views, each of said views including at least one RF excitation pulse for exciting nuclear spins in the object, one 180°
- RF pulse for generating a spin-echo signal, and at least one encoding magnetic field gradient pulse used to encode spatial information into said spin-echo signal, said method comprising the steps of;
applying said encoding magnetic field gradient pulse subsequent to the irradiation of the study object with said 180°
RF pulse, but prior to the occurrence of said spin-echo signal, said encoding magnetic field gradient pulse being applied along at least one directional axis of the study object; andapplying, following the occurrence of said spin-echo signal, a reversing magnetic field gradient pulse so as to undo the effects of said encoding magnetic field gradient pulse on any residual transverse magnitization, the amplitude of said reversing and encoding gradient pulses being selected such that the algebraic sum thereof along said one axis is equal to a constant. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10)
- RF pulse for generating a spin-echo signal, and at least one encoding magnetic field gradient pulse used to encode spatial information into said spin-echo signal, said method comprising the steps of;
Specification