THE ACCURACY OF MAGNETIC-RESONANCE PHASE-VELOCITY MEASUREMENTS IN STENOTIC FLOW

Nuclear magnetic resonance (MR) can be used to measure velocities in f luid flow using the technique of phase velocity mapping. Advantages of MR velocimetry include the simultaneous mapping of the entire how fie ld through a non-contacting, magnetic window. The phase velocity mappi ng technique assumes that velocity is constant over the measurement ti me (typically around 10 ms). For many fluid flows, this assumption is not valid. The current study showed that MR phase velocity measurement s of velocity through stenotic flow can be in error by over 100% immed iately upstream and downstream of the stenosis throat and by 20% far d ownstream of the throat in comparison with laser Doppler anemometer me asurements taken at the same location. Highly turbulent flow also led to significant errors in velocity measurement. These errors can be att ributed to several sources including low signal-to-noise ratio, additi onal phase shifts due to non-constant velocities, and non-stationary t ransit-time effects. Velocity measurement errors could be reduced to u nder 30% at all measurement locations through the use of MR sequences with high signal-to-noise ratios, low echo times, and thick slices. Co pyright (C) 1996 Elsevier Science Ltd.