Method for reduction of MR image artifacts due to flowing nuclei by gradient moment nulling
First Claim
1. A method of compensating for random phase accumulations in magnetic resonance signals acquired from a region of an object having stationary and flowing nuclear spins, said method including the implementation of a plurality of views, each of which includes irradiation of said region by an RF excitation pulse at the Larmor frequency to produce a spin-echo signal at a time TE, and application of a pulsed magnetic field gradient having adjustable amplitude and duration parameters along at least one dimensional axis of said region, said random phase accumulations being due to fluctuations of flow velocity of said flowing spins from view to view, said method comprising the improvement:
- modifying at least one of said amplitude and duration parameters so as to make at least one of the higher moments of said magnetic field gradient equal zero by satisfying for said flowing nuclear spins the equation;
##EQU11## where α
=x, y, or z, v is the velocity of nuclear spin flow in the direction of α
,TE is the time occurrence of the spin-echo signal,G.sub.α
is the gradient in the direction, andγ
is the gyromagnetic ratio.
1 Assignment
0 Petitions
Accused Products
Abstract
A technique has been developed which reduces blood-flow artifacts in multi-echo, multi-slice magnetic resonance (MR) imaging by rephasing spins which have arbitrary velocity as well as static spins. The technique requires tailoring of the gradient structure along at least one of the three axes so as to null out in the preferred embodiment the zeroth and first moments of the gradient distributions.
25 Citations
9 Claims
-
1. A method of compensating for random phase accumulations in magnetic resonance signals acquired from a region of an object having stationary and flowing nuclear spins, said method including the implementation of a plurality of views, each of which includes irradiation of said region by an RF excitation pulse at the Larmor frequency to produce a spin-echo signal at a time TE, and application of a pulsed magnetic field gradient having adjustable amplitude and duration parameters along at least one dimensional axis of said region, said random phase accumulations being due to fluctuations of flow velocity of said flowing spins from view to view, said method comprising the improvement:
-
modifying at least one of said amplitude and duration parameters so as to make at least one of the higher moments of said magnetic field gradient equal zero by satisfying for said flowing nuclear spins the equation;
##EQU11## where α
=x, y, or z, v is the velocity of nuclear spin flow in the direction of α
,TE is the time occurrence of the spin-echo signal, G.sub.α
is the gradient in the direction, andγ
is the gyromagnetic ratio. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8)
-
-
9. A method of compensating for random phase accumulations in magnetic resonance signals acquired from a region of an object having stationary and flowing nuclear spins, said method including the implementation of a plurality of views, each of which includes irradiation of said region by an RF excitation pulse at the Larmor frequency to produce an NMR signal, and application of a pulsed magnetic field gradient having adjustable amplitude and duration parameters along at least one dimensional axis of said region, said random phase accumulations being due to fluctuations of flow velocity of said flowing spins from view to view, said method comprising the steps:
-
(a) selectively exciting nuclear spins in said region in the presence of a first gradient applied along a first dimensional axis of said region so as to produce a spin-echo signal; (b) applying a phase-encoding magnetic field gradient along a second dimensional axis of said region to encode into said spin-echo signal spatial information in the direction of said second axis; (c) observing said spin echo signal in the presence of a readout magnetic field gradient applied along a third dimensional axis of said region orthogonal to said third axis, to encode spatial information along said third axis; and (d) modifying at least one of said amplitude and duration parameters of at least one of said first, second and third magnetic field gradients so as to make at least one of the higher moments of said one magnetic field gradient equal zero by satisfying for said flowing nuclear spins the equation;
##EQU12## where α
=x, y, or z, v is the velocity of nuclear spin flow in the direction of α
,TE is the time occurrence of the spin-echo signal, G.sub.α
is the gradient in the α
direction, andγ
is the gyromagnetic ratio.
-
Specification