Visualization of acoustic streaming produced by a
lithotripsy field using a particle image velocimetry:
preliminary observation
1,6 2 3 3 4
Min Joo Choi , Deog Hee Doh , Chu Hyun Cho , Guen Hie Rim , Kwan Suk Kang and Yoon
5
Jun Lee
1
Department of Medicine, College of Medicine, Cheju National University, Cheju, 690-756,
2
South Korea. Mechanical & Information Engineering, Korea Maritime University, Pusan, South
3
Korea. Applied Electrophysics Research Group, Korea Electrotechnology Research Institute,
4
Changwan, South Korea. Interdisciplinary Postgraduate Program in Biomedical Engineering,
5
Cheju National University, Cheju, 690-756, South Korea, Department of Nuclear & Engergy
6
Engineering, Cheju National University, Cheju, 690-756, South Korea. Medical and Industrial
Ultrasonics, NPL, Teddington, TW11 0LW, UK
Abstract: Extracorporeal shock wave lithotripsy (ESWL) has been known as a revolutionary
technique for the clinical treatment of the stone diseases since the middle of 1980’s. It employs
high amplitude acoustic field focused onto the stones at depth in patients. Although theory
behind the biological effects by the lithotripsy field is not clearly understood, literatures suggest
that the mechanical effects such as cavitation and streaming play important roles in stone
fragmentation. While many scientists have investigated on cavitation in lithotripsy fields for a
long time, but it is hardly seen the study on the acoustic streaming induced by a lithotripsy pulse.
In this study we attempted to observe optical images of the acoustic streaming produced in
water by a lithotripsy pulse using a particle image velocimetry (PIV) technique. The driving
acoustic pulse was produced by a home made electromagnetic experimental lithotripter.
Polystyrene particles of about 10 m in diameters were inserted to water before the PIV
technique was taken for visualizing the fluid flow. Acoustic streaming around the beam focus
was easily noticeable even with our naked eyes over all settings from 8 to 20 kV. The mages
were captured for the region of interest, namely, focal area of a rectangular 80 mm along the
beam axis by 80 mm cross the beam axis, using a CCD camera at a frame rate of 30 fpm. We
carried out an image processing based on a cross correlation method for a series of the images
to estimate the velocity vectors of the particles, i.e., the quantity of streaming in two-dimensional
plane. Spatial distributions of the vector quantities are so complicated and there are a number of
local peaks and vortexes seen. These features make the PIV technique be more preferable to a
conventional streaming velocity measurement using a hot film anemometer at a spatial point. It
was found that values of the peak in streaming velocities increase from 0.3 to 3 cm/s in a
sigmoid pattern as the voltage setting was raised. This is likely attributed to the fact that the
streaming is in general proportional to the field intensity and the similar sigmoid pattern was also
seen in the focal intensity with increasing the setting.