The study of flow by pulsed nuclear magnetic resonance. II. Measurement of flow velocities using a repetitive pulse method

Abstract

A pulsed NMR method that makes possible the measurement of flow velocities of flowing fluid is described. The method employs a regular sequence of identical rf pulses and a linear gradient in the static magnetic field in the direction of flow. Flow velocities of laminar flow in a capillary are measured in the region 1 to 25 mm/sec. A theoretical analysis of the pulse method is given, based on the classical Bloch equations and taking into account a linear field gradient of the static magnetic field and an inhomogeneous distribution of the rf field of the transmitter/receiver coil. A comparison is given of experimental NMR signals and computer simulations. Since a null-signal is detected for stationary samples, the method is especially suitable in biological systems where fluid flow takes place in the presence of stationary fluid.