Accurate acoustic power measurement for low-intensity focused ultrasound using focal axial vibration velocity

Abstract

Low-intensity focused ultrasound is a form of therapy that can have reversible acoustothermal effects on biological tissue, depending on the exposure parameters. The acoustic power (AP) should be chosen with caution for the sake of safety. To recover the energy of counteracted radial vibrations at the focal point, an accurate AP measurement method using the focal axial vibration velocity (FAVV) is proposed in explicit formulae and is demonstrated experimentally using a laser vibrometer. The experimental APs for two transducers agree well with theoretical calculations and numerical simulations, showing that AP is proportional to the square of the FAVV, with a fixed power gain determined by the physical parameters of the transducers. The favorable results suggest that the FAVV can be used as a valuable parameter for non-contact AP measurement, providing a new strategy for accurate power control for low-intensity focused ultrasound in biomedical engineering.

High-speed photography of shock waves with an adaptive illumination

“…Focusing of the shock waves [24][25][26] is exploited in medicine, either as a therapeutic technique employing low-intensity focused ultrasound (LIFU) [27] or high-intensity focused ultrasound (HIFU) [28], where tissue in the focal volume is either stimulated (LIFU) or destroyed by heating (HIFU). Increasing the pressure amplitude brings us to destructive ultrasonic histotripsy [29], where the targeted tissue experiences mechanical breakdown due to intense sonification.…”

Second harmonic magnetoacoustic responses of magnetic nanoparticles in magnetoacoustic tomography with magnetic induction*

“…The tone-burst signal was amplified by the constant-current power supply (HEA-500 G, Foneng, China) to drive the home-made solenoid. A reflective polyethylene terephthalate (PET) membrane with a thickness of 5 µm was stick on the center of the 034302-4 left surface of the MNP solution model to transmit the acoustic vibrations [30] from the inside MNPs. To achieve a stable interference output, the laser sensor was adjusted to ensure the light beam perpendicular to the reflective membrane.…”

Pressure wave propagation effects in the eye after photoablation

“…where f = 10 MHz is the dominant frequency of the acoustic excitation, c = 1500 m/s is the approximate speed of sound in the eye tissues, and  = 0.8 cm −1 is the average pressure attenuation coefficient of the anterior part of the eye 4 . Using this approximate equation 12 and taking into account the acoustic attenuation, the gain is calculated to be 15 for the 2r = 6.5-mm spot, 3.2 for the 2r = 3.0-mm spot and 0.81 for the 2r = 1.5-mm spot. The match between the numerical gain and the approximate, analytically obtained gain is very good, except for the smallest spot, where the additional, 0.75-mm-wide tapper should have been effectively added to the spherical cap size r.…”

“…From the physical point of view, focusing of photoablation-induced mechanical transients is similar to the therapeutic technique employing low-(LIFU) or high-intensity focused ultrasound (HIFU), where tissue in the focal volume is either stimulated (LIFU) 12 or destroyed by heating (HIFU) 13 , or to the destructive ultrasonic histotripsy, where the targeted tissue experiences mechanical breakdown by intense sonification 14 . Here, bursts of multicycle ultrasonic pulses with frequencies in the MHz range or continuous ultrasound are generated by bowl-shaped phased array transducers, resembling the spherical shape of the cornea.…”