title: Flow velocity measurement with ac gradients.
abstract: 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 rf 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.
mesh_terms: D001783:Blood Flow Velocity / Q000379:methods; D005583:Fourier Analysis; D009682:Magnetic Resonance Spectroscopy / Q000379:methods*; D008433:Mathematics; D008961:Models, Structural; D012212:Rheology / Q000379:methods*