A new nuclear magnetic resonance imaging technique for unambiguous unidirectional measurement of flow velocity

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Abstract
A new nuclear magnetic resonance (NMR) flow-velocity-imaging method applied to the study of the fluid dynamics is introduced. In the proposed technique, a selection gradient is used for the phase encoding, and since the selection gradient is relatively small compared with the conventional gradient for phase encoding it allows the measurement of high-velocity flow. To obtain the phase-velocity relationship, the Bloch equation is solved numerically and establishes the quantitative phase-velocity relationship of the flow under the slice selection gradient and echo radio frequency pulse. The flow effect compensation in the directions other than the slice selection direction is achieved by applying additional flow coding gradients similar to the conventional flow phase coding. The experimental NMR flow images obtained with the new technique are compared with the velocity measurements made with a laser Doppler velocimeter, and are found to be in close agreement.