A new method for flow velocity measurement: frequency encoded NMR.
We demonstrate a new rapid NMR method to measure the average velocity and the velocity distribution of a flowing fluid. We use a truncated Carr-Purcel-Meiboom-Gill pulse sequence, pi/2-T-pi-2T-pi-T-echo, in the presence of a static magnetic field gradient. The pi/2 pulse is selective and tags a narrow slice of nuclei. The second echo from the tagged nuclei is Fourier transformed after the nuclei have evolved for a time 4T to give the velocity distribution modified by the initial slice selection profile. In this way, average velocities up to 54 cm/s were measured for water flowing in a plastic tube with either a plug or a developed velocity distribution. Each measurement required about 20 ms but this could be reduced with larger field gradients. Thus, this method is fast enough to apply to such problems as measuring pulsatile flow in arteries.
Caprihan
A
A
Davis
J G
JG
Altobelli
S A
SA
Fukushima
E
E
D000818:Animals; D001783:Blood Flow Velocity; D005583:Fourier Analysis; D006801:Humans; D009682:Magnetic Resonance Spectroscopy / Q000379:methods*; D008961:Models, Structural; D012212:Rheology; D014867:Water
D014867:Water