Studies of water in biological systems by a pulsed NMR method. 1. Flow profile in a cylindrical tube.

Pulsed NMR experiments on water flowing through cylindrical tubes are discussed. Spin echo signals of proton nuclear spins in water molecules were detected RF (radio frequency) phase-sensitively in static magnetic field gradients which were superposed on a main magnetic field. Both the intensity and the RF phase of the spin echo signal depended upon the flow pattern. It is shown that the velocity distribution function was driven from the magnetic field gradient dependence of spin echo signals. Velocity distributions (or velocity profiles) of the fluid in a uniform cylindrical tube have been measured from the spin echo signals. The data on the flow behind a stenosis were widely different from the data on laminar flows.