Acoustical enhancement of nuclear magnetic relaxation rates in liquids

Proton nuclear magnetic relaxation is known to depend on thermal motion. That motion can be affected if an acoustic wave runs through the sample. Nuclear magnetic relaxation was shown to be modified by acoustic waves in solids, but the phenomenon was never observed in liquids. A quantitative estimation is here obtained for liquids whose relaxation is governed by magnetic dipolar coupling, thanks to the calculation of the increment to spectral density functions due to acoustic stimulation. The result of the calculation leads to the conclusion that the effect is negligible for monochromatic excitation if the wave amplitude remains compatible with the safety requirements typical of magnetic resonance imaging.