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

H Wen - Magnetic Resonance in Medicine: An Official Journal …, 2001 - Wiley Online Library
H Wen
Magnetic Resonance in Medicine: An Official Journal of the …, 2001Wiley Online Library
This article presents a two‐dimensional velocity‐selective spin excitation (2D‐VSP) method
that enables quantitative imaging of motion in two directions 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
the speed of motion, while the signal phase represents the direction of motion. Experimental
demonstration is presented in conjunction with an analysis of the accuracy of this method …
Abstract
This article presents a two‐dimensional velocity‐selective spin excitation (2D‐VSP) method that enables quantitative imaging of motion in two directions 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 the speed of motion, while the signal phase represents the direction of motion. Experimental demonstration is presented in conjunction with an analysis of the accuracy of this method. VSP methods are often limited by inconsistent static signal suppression under variable shim and RF conditions. By using adiabatic RF pulses in a 2D‐VSP composite that possesses time‐reversal symmetry, consistent background suppression of 30‐fold or higher was demonstrated over experimental conditions of ±200 Hz off‐resonance and 30% RF field variation. Magn Reson Med 46:767–772, 2001. © 2001 Wiley‐Liss, Inc.
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