Mapping the velocity vector onto the spin vector: Two-dimensional velocity-selective spin excitation for MR flow imaging

This article presents a two-dimensional velocity-selective spin excitation (2D-VSP) method that enables quantitative imaging of motion in two directio ns in a single scan, without the need for image subtraction or combination. It Is based on the idea of mapping a 2D velocity vector directly onto the transverse magnetization vector, such that the signal intensity reflects th e speed of motion, while the signal phase represents the direction of motio n. Experimental demonstration is presented in conjunction with an analysis of the accuracy of this method. VSP methods are often limited by inconsiste nt static signal suppression under variable shim and RF conditions. By usin g adiabatic RF pulses in a 2D-VSP composite that possesses time-reversal sy mmetry, consistent background suppression of 30-fold or higher was demonstr ated over experimental conditions of +/- 200 Hz off-resonance and 30% RF fi eld variation. Published 2001 Wiley-Liss, Inc.(dagger).