Flow velocity measurement with ac gradients

Two NMR experiments are described that use ac field gradients to measure flow velocities. Both experiments perform no spacial localization; instead, fluid velocity is converted to a resonance frequency shift. Thus, by Fourier transformation of a single FID or echo train the distribution of velocities is available. The first experiment uses only one of pulse but requires a homogeneous static field. The second experiment uses the CPMG multiple‐pulse sequence to refocus the effects of field inhomogeneity and chemical shifts. Results are shown for both experiments using a simple flowing phantom. Applications of the techniques to time‐resolved blood flow measurement are discussed. © 1987 Academic Press, Inc.