Gwansuk Kang

Characterization of the shock pulse-induced cavitation bubble activities recorded by an optical fiber hydrophone

A shock pressure pulse used in an extracorporeal shock wave treatment has a large negative pressure (<-5 MPa) which can produce cavitation. Cavitation cannot be measured easily, but may have known therapeutic effects. This study considers the signal recorded for several hundred microseconds using an optical hydrophone submerged in water at the focus of shock pressure field. The signal is characterized by shock pulse followed by a long tail after several microseconds; this signal is regarded as a cavitation-related signal (CRS). An experimental investigation of the CRS was conducted in the shock pressure field produced in water using an optical hydrophone (FOPH2000, RP Acoustics, Germany). The CRS was found to contain characteristic information about the shock pulse-induced cavitation. The first and second collapse times (t1 and t2) were identified in the CRS. The collapse time delay (tc = t2 - t1) increased with the driving shock pressures. The signal amplitude integrated for time from t1 to t2 was highly correlated with tc (adjusted R(2) = 0.990). This finding suggests that a single optical hydrophone can be used to measure shock pulse and to characterize shock pulse-induced cavitation.

Activities of the cavitation bubbles in the wake of a shock pressure pulse recorded by an optical fiber hydrophone

The shock pulse used in an extracorporeal shock wave treatment (ESWT or ESWL) has a large negative pressure (< -5MPa) which can always produce acoustic cavitation. The resulting cavitation bubbles are known to play an important role in therapeutic effects, however, the bubble activities are not readily measurable yet. The present study considered a weird tail after the negative peak in the time history of pressure sensed by an optical fiber hydrophone which was usually abandoned in typical pressure field measurements. A shock pressure pulse in water causes change of mass density which modulates the optical refractive index. The change of the refractive index can be measured by the light reflection at the tip of the glass fiber submerged in water. The loss of water contact by cavitation bubbles at the fiber tip leads to an abnormal increase of high reflection which is clearly identified. This suggests that the weird tail of the hydrophone signal beyond the negative cycle of a shock pulse is closely related...

Ultrasonic standing wave patterns in a petri-dish

A standing wave is well developed in a petri-dish used for cell culture, which is subject to the height of the culture fluid. A simple acoustic theory states that the pressure at the bottom of the petri-dish varies from 0 to its maximum while the height varies over a half wave length of the driving ultrasound. This suggests that the standing wave pattern should be taken into account when the cell line in a petri-dish is exposed to ultrasound. The present study has experimentally verified the theoretical prediction using the pressure sensitive film attached to the bottom of the petri-dish, when water, instead of the culture fluid, was contained in the dish. The driving field was made of 1 MHz transducer (V316, Panametrics, USA). Gradual destructuring of the standing wave patterns was observed as the driving power increased and, thus, the surface of water was becoming more fluctuating. Keywords, standing wave, petri-dish, cell, culture fluid, monitoring

Comparison of spatial distribution characteristics of shock wave pressure field and cavitation bubble cloud

This study aims to compare the spatial characteristics of the cavitation bubble cloud and shockwave pressure field. Cavitation bubble cloud images were acquired using micro pulsed light with 150us exposure time and CCD camera, and images were accumulated after repeated several acquisitions. The shockwave field was measured using an optical hydrophone to compare with the distribution of cavitation bubbles. After the shockwave device was triggered, cavitation bubbles were generated and visualized during 150us light exposure and were collapsed at the same position where they were generated. Most of the bubbles are concentrated in the focal region of the shockwave. The largest bubbles were observed at the peak negative pressure position in the focal area In the remaining focal area, it was formed as relatively small bubbles. Outside the focal area, very small bubbles were sparsely observed. Cavitation bubbles produced by a single shockwave pulse are highly correlated with the shockwave pressure at exposed loc...

Visualization of the cavitation bubbles produced by a clinical shock wave field using a micropulse LED light

Extracorporeal shock wave therapy employs intense shock waves that produce cavitation bubbles understood to play an important role in therapeutic effects. This study considers shock-wave-induced cavitation bubbles, expected to be closely associated with treated therapeutic regions. A simple optical method was devised to visualize the cavitation bubbles under micropulse LED light illumination and to capture an afterimage of the bubbles for their entire lifetime from formation to collapse. The optical images of the cavitation bubbles produced by a clinical shock wave therapeutic device were shown to preserve the characteristics of the focusing shock wave field. The similarity of the characteristics may enable the cavitation cloud image to provide the intensity and location of shock wave irradiation for the clinical quality assurance of therapeutic devices. Further research that includes the dynamic effects in the static images of cavitation bubbles is suggested.

Geometrical characterization of the cavitation bubble clouds produced by a clinical shock wave device

This study was to optically visualize the cavitation bubbles produced by a clinical shock wave and to look into their geometric features of the resulting cavitation bubbles in relation to the driving shock wave field. A clinical shock wave therapeutic system was taken for shock wave production. The shock wave induced cavitation bubbles were captured by a professional camera under the illumination of a micro-pulse LED light. The light exposure was set to last for the whole life time of bubbles from formation to subsequent collapses. It was shown that the cavitation bubbles appeared mostly in the vicinity of the focus. The bubbles became more and larger as approaching to the focus. The cavitation bubbles formed jet streams which became enlarged (stronger) as the shock wave device output setting increased. The bubble cloud boundary was reasonably fitted to an elongated ellipsoid characteristically similar to the acoustic focal area. The bubble clouds were enlarged as the output setting increased. The geometric features of the cavitation bubbles characteristically similar to those of the focusing acoustic field have potential to provide the therapeutic focal information without time consuming hydrophone measurements of the shock wave field causing damages of the expensive sensor. The present study is limited to the static afterimages of the cavitation bubbles and investigation including the bubble dynamics is suggested to deliver the more realistic therapeutic area of the shock wave therapy

The role of the acoustic radiation force in color Doppler twinkling artifacts

Purpose: The aim of this experimental study was to evaluate whether the acoustic radiation force (ARF) is a potential source of twinkling artifacts in color Doppler images. Methods: Color Doppler images were obtained using a clinical ultrasonic scanner (Voluson e, GE Healthcare) for a high contrast (+15 dB) circular scattering phantom at pulse repetition frequencies (PRFs) ranging from 0.1 to 13 kHz. Ultrasound transmissions resulting in ARF were measured using a hydrophone at the various PRFs considered. The influence of ARF on the appearance of twinkling colors was examined via the common parameter PRF. This methodology is based on the fact that alternating positive and negative Doppler shifts induced by the ARF are centered at a PRF twice the maximum Doppler frequency on the color scale bar, whereas the twinkling color aliasing is expected to remain similar regardless of PRF. Results: Color twinkling artifacts were observed to be most conspicuous at the lowest PRF of 0.1 kHz. The extent of twinkling rapidly decreased as the PRF increased, eventually disappearing when the PRF ≥0.6 kHz. The measured ultrasound transmissions, however, were found to be insensitive to the PRF, and therefore it can be inferred that the PRF was insensitive to the ARF. Conclusion: Based on our experimental observations, the ARF may not be a source of color Doppler twinkling artifacts.