Acoustic radiation force (ARF) has been used in many medical applications, the most notable of which is measuring the stiffness of soft tissues. The ARF used in these applications results from the dissipation of acoustic energy due to scattering and absorption of sound and, accordingly, may be called dissipative ARF. Another source of ARF, which is not related to dissipation of acoustic energy in a medium, is variation in acoustic energy density due to gradients of compressional wave speeds in the medium. The effects of this non-dissipative ARF (nARF) are most pronounced in sonication of the medium by short ultrasonic pulses with durations on the order of microseconds. Experiments with tissue-mimicking gelatin blocks and various excised animal tissues demonstrated the possibility of measuring sub-nanometer range displacements induced by nARF acting on interfaces in materials with different compressional wave speeds. A continuous wave Doppler device was used to measure the interface particle velocity. Demonstrating the possibility of using Doppler signal processing to extract the nanometer-order motion induced by the nARF could open new areas for ultrasound imaging and tissue characterization such as the creation of a new mode of ultrafast elastography.

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