NMR detection of low magnetization levels in flowing fluids

Nuclear magnetic resonance (NMR) signals were recorded from ordinary tap water 12 s after the fluid was magnetized upstream of the detector. Detection time was extended to 18 s with signal averaging. The time for a bolus of magnetized water to reach the NMR detector was varied. Based on the measured signal amplitude, a relaxation time T1of approximately 2.5 s was graphically determined. Since the NMR signal was detected after 7 time constants, these findings suggest that NMR tag-detect systems are useful over distances involving several time constants, such as those encountered in the measurement of blood flow in biological systems. These findings are similar to the previously published studies of Kudravcev and Bowman. Measurements of the T1of human blood indicate that T1is dependent on the degree of oxygenation of the blood.