Ultrasound generation and high-frequency motion of magnetic nanoparticles in an alternating magnetic field: Toward intracellular ultrasound therapy?

We show theoretically that, in an inhomogeneous alternating magnetic field of frequency f, due to the alternating gradient, magnetic nanoparticles oscillate mechanically and generate ultrasound waves. This effect is maximized and better controlled if a static magnetic field is superimposed to an alternating gradient. It makes possible the generation of ultrasounds intracellularly and might also explain recent experiments in magnetic hyperthermia in which cells have been killed without any global temperature increase. Combined to an efficient targeting, it could permit ultrasound therapy with an unprecedented spatial resolution.