Secondary Shock Wave Research Articles

Secondary shock wave emissions from cavitation in lithotripsy

We investigate the role of secondary shock waves (SSWs) generated by cavitation in lithotripsy. Acoustic pressure was measured with a fiber optic probe hydrophone and cavitation using a dual passive cavitation detector (PCD) consisting of two confocal transducers. An artificial stone (∼7 mm diameter and ∼9 mm length) was placed at the focus of an electrohydraulic lithotripter. The fiber was inserted through a hole drilled through the stone so that the tip was at the proximal surface. SSWs were identified by matching the time of arrival to that of the inertial collapse signature acquired by the PCD. Measurements of SSWs were obtained for 50% of SWs fired at 20 kV and 1 Hz. The peak positive pressure for the SSW was p+=33.7±14.8 MPa, which was comparable to the pressure induced by the incident SW (p+=42.6±6 MPa). The peak pressure in water was p+=23.2±4.4 MPa. The PCD also recorded acoustic emissions from forced collapse of pre-existing bubbles caused by the incident SW. We propose that both the reflection from the semi-rigid stone boundary and SSW from the forced collapse contribute to the observed increase in the peak pressure of the incident SW in presence of a stone. [Work supported by NIH.]

Underwater acoustics and cavitating flow of water entry

The fluid mechanics of water entry is studied through investigating the underwater acoustics and the supercavitation. Underwater acoustic signals in water entry are extensively measured at about 30 different positions by using a PVDF needle hydrophone. From the measurements we obtain (1) the primary shock wave caused by the impact of the blunt body on free surface; (2) the vapor pressure inside the cavity; (3) the secondary shock wave caused by pulling away of the cavity from free surface; and so on. The supercavitation induced by the blunt body is observed by using a digital high-speed video camera as well as the single shot photography. The periodic and 3 dimensional motion of the supercavitation is revealed. The experiment is carried out at room temperature.

Feshbach resonance induced shock waves in Bose-Einstein condensates.

We propose a method for generating shock waves in Bose-Einstein condensates by rapidly increasing the value of the nonlinear coefficient using Feshbach resonances. We show that in a cigar-shaped condensate there exist primary (transverse) and secondary (longitudinal) shock waves. We analyze how the shocks are generated in multidimensional scenarios and describe the related phenomenology.

Interferometric CT measurement of three-dimensional flow phenomena on shock waves and vortices discharged from open ends

Three-dimensional flow phenomena are observed in a shock tube experiment for shock waves and vortices discharged from a square open end and a pair of circular open ends by using an interferometric CT (Computed Tomography) technique. To take multidirectional finite-fringe interferograms for a three-dimensional flow field, we introduce a rotating duct model in the test section of the shock tube. The experiments are performed for incident shock Mach numbers 1.50 and 1.30 in nitrogen gas of 98 kPa initial pressure. Good quality CT images of the density distribution are obtained by carefully selecting the projection images for a reproducible flow within a prescribed accuracy. The three-dimensional flow features are clearly visualized for a vortex ring, a secondary shock wave, shock-vortex interaction, and shock-shock interaction through the pseudo-color image of density distribution and the isopycnic surface. Their meanings in gas dynamics and shock dynamics are discussed. We demonstrate that studies of various three-dimensional problems in shock dynamics are possible using the present CT technique.

Dynamics of concerted bubble cluster collapse in shock wave lithotripsy

Cavitation bubble cluster collapse at the surface of artificial kidney stones during shock wave lithotripsy was investigated in vitro by means of multiframe high-speed photography, passive cavitation detection (PCD), and pressure waveform measurements using a fiber-optic probe hydrophone (FOPH). It was observed that after the passage of the lithotripter shock pulse the stone was covered by numerous individual bubbles. During their growth phase the bubbles coalesced into bubble clusters, with the biggest cluster at the proximal face of the stone. High-speed camera images suggested that cluster collapse started at the periphery and ended with a violent collapse in a small region in the center of the surface of the stone. Shadowgraphy resolved numerous secondary shock waves emitted during this focused collapse. Shock wave emission during cluster collapse was confirmed by PCD. Measurement with the FOPH showed that these shock waves were typically of short duration (0.2 μs). The majority of the shock waves emanating from cluster collapse were low amplitude but some shock waves registered amplitudes on the order of the incident shock pulse (tens of MPa). [Work supported by NIH DK43881, DK55674.]

Three-dimensional propagation of the transmitted shock wave in a square cross-sectional chamber

An investigation into the three-dimensional propagation of the transmitted shock wave in a square cross-section chamber was described in this paper, and the work was carried out numerically by solving the Euler equations with a dispersion-controlled scheme. Computational images were constructed from the density distribution of the transmitted shock wave discharging from the open end of the square shock tube and compared directly with holographic interferograms available for CFD validation. Two cases of the transmitted shock wave propagating at different Mach numbers in the same geometry were simulated. A special shock reflection system near the corner of the square cross-section chamber was observed, consisting of four shock waves: the transmitted shock wave, two reflection shock waves and a Mach stem. A contact surface may appear in the four-shock system when the transmitted shock wave becomes stronger. Both the secondary shock wave and the primary vortex loop are three-dimensional in the present case due to the non-uniform flow expansion behind the transmitted shock.

Numerical investigation of transient nozzle flow

Abstract. The starting process of two-dimensional and axisymmetric nozzle flows has been investigated numerically. Special attention has been paid to the early phase of the starting process and to the appearance of a strong secondary shock wave. For both cases, shock intensities and velocities are obtained and discussed. The flow evolution in the axisymmetric case is proved to be more complex and the transient starting process is slower than in the plane case. Finally, the effects of changing the nozzle angle and the incident shock wave Mach number on the transient flow are addressed. It is shown that a faster start-up can be induced either by decreasing the nozzle angle or increasing the Mach number of the incident shock wave.

エネルギー授受およびローレンツ力が存在する超音速流れの挙動

The behavior of supersonic flow under the energy exchange and the Lorentz force was studied analytically. The shock relations (MHD Rankine-Hugoniot relations) including the energy exchange and the Lorentz force were derived for the first time. The relations indicate that the shock wave strength can be weakened by the energy addition or the negative Lorentz force acting upstream and that the weakening of shock wave is always accompanied by total pressure loss. The relation between the isentropic efficiency and the enthalpy extraction of the MHD generator was derived using the MHD Rankine-Hugoniot relations, the interaction parameter and the electrical efficiency. The derived relation suggests that shock wave tends to appear at lower isentropic efficiency and this agrees with experimental results qualitatively. Effects of the energy exchange and the Lorentz force on velocity of propagation shock wave were also studied by one-dimensional numerical simulation. The results show that the reflected shock wave and the secondary shock wave appear under a certain condition. Furthermore, it is shown that the velocity of the propagation shock wave can be controlled by the energy exchange and the Lorentz force.

Tandem shock wave cavitation enhancement for extracorporeal lithotripsy

Extracorporeal shock wave lithotripsy (ESWL) has been successful for more than twenty years in treating patients with kidney stones. Hundreds of underwater shock waves are generated outside the patient's body and focused on the kidney stone. Stones fracture mainly due to spalling, cavitation and layer separation. Cavitation bubbles are produced in the vicinity of the stone by the tensile phase of each shock wave. Bubbles expand, stabilize and finally collapse violently, creating stone-damaging secondary shock waves and microjets. Bubble collapse can be intensified by sending a second shock wave a few hundred microseconds after the first. A novel method of generating two piezoelectrically generated shock waves with an adjustable time delay between 50 and 950 µs is described and tested. The objective is to enhance cavitation-induced damage to kidney stones during ESWL in order to reduce treatment time. In vitro kidney stone model fragmentation efficiency and pressure measurements were compared with those for a standard ESWL system. Results indicate that fragmentation efficiency was significantly enhanced at a shock wave delay of about 400 and 250 µs using rectangular and spherical stone phantoms, respectively. The system presented here could be installed in clinical devices at relatively low cost, without the need for a second shock wave generator.

Effect of percutaneous nephrolithotomy on differential renal function as measured by mercaptoacetyl triglycine nuclear renography

Objectives. To determine the impact on differential renal function of percutaneous nephrolithotomy for complex renal calculi. Methods. From July 1999 to December 2000, 45 patients underwent percutaneous nephrolithotomy. Of these, 19 agreed to participate in the study. All patients completed a quantitative assessment of differential renal function preoperatively and postoperatively with technetium 99m mercaptoacetyl triglycine nuclear renography and serum creatinine measurements. Results. The mean patient age was 49 years (range 11 to 75) for the 13 female and 6 male patients. The mean stone burden was 1432 mm 2 (range 156 to 5220). The mean surgical time was 2.57 hours (range 1.17 to 5.08). The median hospital stay was 2.0 days (range 1 to 19). Of the 19 patients, 13 (68%) were stone free after one procedure. Four patients underwent ureteroscopy with stone extraction for residual fragments. One patient underwent secondary extracorporeal shock wave lithotripsy. One patient underwent nephrectomy for poor renal function. Renal function, for the entire group, increased from 36.8% preoperatively to 38.5% postoperatively. Renal function was preserved in 16 (84%) of 19 patients, including improvement of function in 7 (37%) of 19 patients. Serum creatinine was unchanged in the two groups. Conclusions. Percutaneous nephrolithotomy does not result in loss of renal function when treating complex renal calculi as measured by nuclear scintigraphy. Operative and hospitalization times were decreased compared with historical open nephrolithotomy and stone clearance was similar.

衝撃波の放出によって誘起される管開口端近くにおける非定常流れの可視化

When the shock wave propagating the straight circular tube reaches at the open end, the impulsive wave is generated by the emission of a shock wave from an open end and the unsteady pulse jet is formed near the open end behind the impulsive wave under the specific condition. This paper aims to clear the mechanism of generating the unsteady pulse jet near the open end and the numerical analysis carried out for the emission of propagating the shock wave from an open end of a tube in this study. The flow field is visualized by the computed shadowgraph method using the axisymmetric two-dimensional density distribution contained the axis, which is obtained by the numerical calculation. In this paper, the mechanism of generating the unsteady pulse jet and the characteristics of a pressure distribution in the flow field, the secondary and spherical shock waves behind the impulsive wave are discussed.

Cavitations in biological tissues

An important reason for the high popularity of diagnostic ultrasound is its lack of hazardous side effects. However, as described below, the probability of inducing undesirable thermal and mechanical effects in tissue increases with a rise in the output of diagnostic ultrasound machines. The use of increasing negative peak pressures of the applied ultrasound pulse enhances the risk of inducing cavitation inside the body. The potential damage of cavitation results from the dynamic, e. g. wild pulsation, and a collapse of bubbles in the respective sound field. The collapse, especially, releases a high amount of energy, related to secondary effects like shock waves, jet formation and the formation of free radicals. To estimate the likelihood of cavitation and ensuing mechanical biological effects the so-called mechanical index was defined. Nowadays, the mechanical index is displayed in real-time on modern diagnostic ultrasound machines. Echo-contrast agents play an increasing role in sonography. These stabilised gas particles increase the likelihood of cavitation formation and the occurrence of other biological side effects. The potential for mechanically induced side effects of diagnostic ultrasound was tested in many animal studies. As for the use of ultrasound for diagnostic purposes, adverse side effects, like haemorrhage or rupture of capillaries, were only observed in the presence of tissue-gas interfaces - as found in the lung or the intestine - or with high concentrations of contrast media. Even though no adverse effects of diagnostic ultrasound have been reported in humans, potentially damaging effect of advanced ultrasound techniques cannot be denied. Various ultrasound organizations, e.g. WFUMB, have therefore formulated recommendations for the safe use of diagnostic ultrasound.

Interaction of shock waves with cavitation bubble: Application of Ho:YAG pulse laser irradiation for cerebral thrombolysis

This paper reports on the application of underwater shock waves and vapor cavities for cerebral thrombolysis. The energy source was a Q-switched Ho:YAG laser (Nippon Infrared Industries Co., Ltd.) with 91 and 140 mJ/pulse energy measured at the end of a 0.60-mm-diam glass optical fiber, pulse duration of 200 ns, and wavelength of 2100 nm. The whole sequences of the shock-wave propagation and growth of the cavitation bubbles from the end of the optical fiber were visualized by high-speed photography using an Imacon 468 camera (Hadland Photonics Ltd.). The shock-wave generation was associated with the laser breakdown in the water. The laser interaction produced a microplasma and heated the liquid in front of the fiber. The plasma drove spherical shock wave in water, followed by the formation of a high-temperature vapor cavity. Collapse of the cavity produced a secondary spherical shock wave in water. Successive generation and collapse of the bubbles were visualized. Pressure histories were measured by PVDF needle hydrophones. The underwater shock waves and the vapor cavities were successfully applied for disruption of artificial thrombosis. The result clearly shows potential extension of this method to precise medical treatment for revascularization in neurosurgery.

Optical Observation of the Supercavitation Induced by High-Speed Water Entry

When a high-speed projectile penetrates into water, a cavity is formed behind the projectile. The gas enclosed in the cavity experiences a nonequilibrium process, i.e., the gas pressure decreases as the projectile moves more deeply into water. As a result, the cavity is sealed near the free surface (surface closure) and subsequently the cavity breaks up in water (deep closure). Accompanying the break-up of the cavity, secondary shock waves appear. This is the so-called supercavitation in water entry. This paper describes an experimental investigation into the water entry phenomenon. Projectiles of 342 m/s were generated from a small-bore rifle that was fixed vertically in the experimental facility. The projectiles were fired into a windowed water tank. A shadowgraph optical observation was performed to observe the entry process of the projectile and the formation and collapse of the cavity behind the projectile. A number of interesting observations relating to the motion of the free surface, the splash, the underwater bubbly flow and so on were found. [S0098-2202(00)00204-2]

Appendix

Appendix

Dusty Gas Flow in a Converging-Diverging Nozzle

The flow in a converging-diverging nozzle is studied numerically. The flowing medium is a suspension composed of gas seeded with small, spherical, solid particles. The solution covers the entire flow history, from its initiation and until a steady state flow is reached. The covered flow domain includes both the flow field inside the nozzle and part of the free jet flow outside of the nozzle exit plane. The solution is repeated for different solid particle diameters, ranging from 0.5 μm to 50 μm, and different dust loading ratios. It is shown that the presence of solid particles in the flow has a significant effect on the developed flow field, inside and outside the nozzle. In particular, by a proper choice of particles diameter lateral pressure waves and the secondary shock wave can be significantly attenuated. The solid particles size has also a marked effect on the position and size of the Mach disk appearing in the free jet flow. It is also shown that in a suspension case a steady state flow is reached faster than in a similar pure gas flow.

Shock wave-inertial microbubble interaction: a theoretical study based on the Gilmore formulation for bubble dynamics.

The Gilmore formulation for bubble dynamics coupled with zeroth-order gas diffusion were used to investigate theoretically the cavitation activity produced by a modified XL-1 lithotripter [J. Acoust. Soc. Am. 105, 1997-2009 (1999)]. The model calculation confirms many of the basic features in bubble dynamics observed experimentally, in particular the strong secondary shock wave emission generated by in situ lithotripter shock wave-inertial microbubble interaction. In addition, shock wave-inertial microbubble interaction produced by a Dornier HM-3, the most commonly used clinical lithotripter, was evaluated. It was shown that the forced collapse of inertial microbubbles with strong secondary shock wave emission could be produced consistently, provided that an appropriate preceding shock wave and interpulse delay were used. Further, it was demonstrated that truncation of the tensile stress of the lithotripter shock wave could significantly reduce the large expansion of the bubble following shock wave-inertial microbubble interaction, which may alleviate the risk for vascular injury during shock wave exposure.

Shock wave-inertial microbubble interaction: methodology, physical characterization, and bioeffect study.

A method of generating in situ shock wave-inertial microbubble interaction by a modified electrohydraulic shock wave lithotripter is proposed and tested in vitro. An annular brass ellipsoidal reflector (thickness = 28 mm) that can be mounted on the aperture rim of a Dornier XL-1 lithotripter was designed and fabricated. This ring reflector shares the same foci with the XL-1 reflector, but is 15 mm short in major axis. Thus, a small portion of the spherical shock wave, generated by a spark discharge at the first focus (F1) of the reflector, is reflected and diffracted by the ring reflector, producing a weak shock wave approximately 8.5 microseconds in front of the lithotripter pulse. Based on the configuration of the ring reflector (different combinations of six identical segments), the peak negative pressure of the preceding weak shock wave at the second focus (F2) can be adjusted from -0.96 to -1.91 MPa, at an output voltage of 25 kV. The preceding shock wave induces inertial microbubbles, most of which expand to a maximum size of 100-200 microns, with a few expanding up to 400 microns before being collapsed in situ by the ensuing lithotripter pulse. Physical characterizations utilizing polyvinylidene difluoride (PVDF) membrane hydrophone, high-speed shadowgraph imaging, and passive cavitation detection have shown strong secondary shock wave emission immediately following the propagating lithotripter shock front, and microjet formation along the wave propagation direction. Using the modified reflector, injury to mouse lymphoid cells is significantly increased at high exposure (up to 50% with shock number > 100). With optimal pulse combination, the maximum efficiency of shock wave-induced membrane permeabilization can be enhanced substantially (up to 91%), achieved at a low exposure of 50 shocks. These results suggest that shock wave-inertial microbubble interaction may be used selectively to either enhance the efficiency of shock wave-mediated macromolecule delivery at low exposure or tissue destruction at high exposure.

Shock physics for nonideal detonations of metallized energetic explosives

The nonideal behavior of condensed explosives with metal particle loading has been studied by many researchers. These previous studies have shown that the explosives behavior is different than that predicted by equilibrium codes (generally lower detonation velocities and pressures are observed or measured), although under many circumstances an increase in performance of metallized explosives is observed. To investigate these phenomena, an unsteady, one-dimensional model is presented that simulates the buildup toward steady detonation of an organic explosive (HMX) containing dispersed aluminum (A1) particles. Heat liberated by secondary oxidation reactions of A1 with the products of the initial decomposition of the explosive is modeled, and parametric studies are presented in which the delay time and the rate of the A1 reactions are varied. Endothermic processes are also considered. Results indicate that induction delay for the A1 particles, combined with endothermic processes, alter the structure of the reaction zones and produce a secondary shock wave that never reaches the detonation wave front. The results of the model are shown to be in agreement with the observed nonideal behaviors of metallized explosives. Future work with the model will include the interaction of the predicted reaction zone structure with a compressible media.

CONTROLLED, FORCED COLLAPSE OF CAVITATION BUBBLES FOR IMPROVED STONE FRAGMENTATION DURING SHOCK WAVE LITHOTRIPSY

The feasibility of using controlled, forced collapse of cavitation bubbles for improved stone fragmentation during shock wave lithotripsy was demonstrated using microsecond tandem shockwave pulses. High-speed photography revealed that a secondary shock wave, released in less than 500 microseconds (micro sec.) following a lithotripter-generated shock wave, can be used to control and force the collapse of cavitation bubbles toward target concretions. This timely enforced shockwave-bubble interaction was found to greatly enhance the cavitational activity near the stone surface, with a resultant up to 43% increment in stone fragmentation. Since most of the cavitation energy is directed and concentrated toward the target stones and fewer shock waves are needed for successful stone comminution, tissue injury associated with this new lithotripsy procedure may also be reduced. This novel concept of shock wave lithotripsy may be used to improve the treatment efficiency and safely of existing clinical lithotripters, as well as in the design of new shock wave lithotripters.