Ultrasonic measurement of minute displacement of object cyclically actuated by acoustic radiation force

Recently, several researchers have investigated the potential of the use of acoustic radiation force for imaging the mechanical properties of tissue. However, these methods have some problems as to safety and the spatial resolution. Therefore, an alternative ultrasonic remote actuation and measurement method is proposed in this paper, in which the intensity of the applied continuous ultrasonic wave is suppressed to be lower than the safety guideline (I W/cm²) recommended by the Japan Society of Ultrasonics in Medicine (JSUM). A minute displacement with amplitude of less than I UJTI is cyclically generated by the radiation force with a low frequency Δf of several hertz. For simultaneous measurement of the minute displacement, cyclic radiation force is applied intermittently by maintaining its envelope waveform of the low-frequency component of Δf Hz. At the same time, an ultrasonic correlation-based method, namely, the phased tracking method, is employed to measure the minute displacement. In basic experiments, the minute displacement of several micrometers was generated in silicone rubber by applying radiation force, and it was successfully measured by the phased tracking method.