QUANTITATIVE MAGNETIC-RESONANCE FLOW IMAGING

Time-of-flight and phase shift methods have both been used for vascula r imaging with magnetic resonance. Phase methods, and phase contrast i n particular, are well suited to quantitative measurements of velocity and volume flow rate. The most robust methods for measuring flow enco de through-plane velocity into phase shift and compute flow by integra ting the measured velocity over the vessel lumen. The accuracy of the flow data can be degraded by the effects of acceleration and eddy curr ents and by partial volume effects, including the effects of finite sl ice thickness and resolution, pulsatile waveforms, motion, and chemica l shift. The reproducibility depends on the signal-to-noise of the dat a and the strength of the flow encoding and can be degraded by inconsi stent definition of the vessel boundary. The adjustable flow sensitivi ty inherent in this method is a particular asset, allowing phase contr ast flow measurement to operate over a dynamic range exceeding 10(5). Recently developed rapid imaging methods are helpful in applications t hat would be compromised by respiratory motion. With care, excellent q uantitative data can be quickly obtained in vivo, and the resulting fl ow information is valuable for the diagnosis and management of a varie ty of conditions.