Acoustic radiation force acting on a spherical scatterer in water: Measurements and simulation

Abstract

Acoustic radiation force (ARF) is successfully used in a recently proposed ultrasonic technology for kidney stone propulsion. The planning of the treatment requires calibration of ARF for stones of different dimensions and locations. However, such calibration remains a problem. Here, a method of measuring ARF acting on a mm-sized spherical object positioned on the axis of a focused ultrasound beam is proposed and tested. Acoustic field was generated by a single-element 1.072 MHz transducer of 100 mm aperture and 70 mm focal length positioned at the bottom of the water tank. Measurements were performed for nylon and glass spherical scatterers with diameters from 2 to 4 mm located at different distances from the source along the vertical beam axis. For each scatterer, the source power was gradually decreased until the scatterer started to fall down from the trap. At this threshold power of the source, the value of ARF was determined as a difference between the gravity and buoyancy forces acting on the scatterer. At other source power outputs, the value of ARF was linearly scaled. ARF was also calculated from pressure distributions reconstructed from acoustic hologram of the source and physical parameters of the scatterers. Experimental and theoretical results were found in a good agreement. It was shown that the most effective pushing was observed at distances where the beam was slightly wider than the scatterer. [Work supported by the stipend of the President of Russia (SP-2621.2016.4), RFBR №18-32-00659, and NIH P01 DK43881.]