NMR multiple-echo phase-contrast blood flow imaging

A method for magnetic resonance imaging of fluid flow in a sample, comprising the steps of:

• (a) immersing the sample in a static magnetic field disposed in a first direction;
• (b) applying a first sequence of magnetic field gradients and radio-frequency signals to the sample to both define a slab, of the sample to be imaged, in a plane substantially orthogonal to a selected direction for which flow velocity is to be measured, and to obtain a plurality N of spin-echo response signals from that slab;
• (c) processing the plurality of first sequence spin-echo signals to obtain a complex value A.sub.1 (X,Y,Z) relating both the spin density .rho.'(X,Y,Z) , . . . and the phase rotation .phi.(X,Y,Z), induced by the first sequence, for each of a selected number of sequential locations (X,Y,Z) in the sample slab;
• (d) applying a second sequence of magnetic field gradient and radio-frequency signals to both define the same sample slab as in step (b) and to obtain another plurality N of spin-echo response signals from that slab;
• (e) including a waveform in at least one of the magnetic field gradient and radio-frequency signals applied in step (d) for imparting to each of the spin-echo signal components from each slab location having a flowing material therein a phase rotation dependent upon the magnitude of the flow velocity therein in the selected direction;
• (f) processing the plurality of second sequence spin-echo signals to obtain a complex value A.sub.2 (X,Y,Z) relating the spin density .rho.'(X,Y,Z) and the imparted phase rotation of the sample material along the selected flow measurement direction for each of the sequential locations (X,Y,Z) in the sample slab;
• and
• (g) processing the complex values A.sub.1 (X,Y,Z) and A.sub.2 (X,Y,Z) for each sample location to obtain a differential phase-contrast value related to the velocity of the flowing material therein in the selected measurement direction.