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May 1988

Volume 83, Issue S1, pp. S1-S122

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back to top Session OO. Physical Acoustics VI and Bioresponse to Vibration III: Extracorporeal Shock Wave Lithotripsy—Biological Aspects
Invited Papers
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Cavitation in lithotripsy (A)

Edwin L. Carstensen

J. Acoust. Soc. Am. Volume 83, Issue S1, pp. S88-S88 (1988); (1 page)

Online Publication Date: 13 Aug 2005

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The pressure amplitudes of the shock waves used in lithotripsy far exceed thresholds for transient cavitation. Where appropriate nuclei exist within the body, it is highly probable that bubbles will form and collapse violently, giving rise to potentially undesirable side effects of the treatment. Evidence from basic and clinical studies in support of this conclusion is accumulating rapidly. Drosophila larvae have served as useful biological models for studies of cavitation‐related phenomena because of the highly reproducible microbubbles within their respiratory system. Using approximately 100 000, 1‐μs pulses from a 2‐MHz piezoelectric source, the threshold for killing of larvae occurs at a pressure amplitude of ∼0.7 MPa. With an electrohydraulic (unfocused spark source) lithotripter, three positive spikes of ∼ 1 MPa are sufficient to kill roughly one‐half of the exposed larvae. This is two orders of magnitude less than the largest reported pressures for clinical lithotripters.
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Materials fragmentation by shock waves (A)

B. Finlayson, Mohamed Nasr, and J. Paul Whelan

J. Acoust. Soc. Am. Volume 83, Issue S1, pp. S88-S88 (1988); (1 page)

Online Publication Date: 13 Aug 2005

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Although extracorporeal shock wave lithotripsy (ESWL) is an important technique, the details of how it works—how shock waves interact with stones to cause disruption—and how to optimize its effect are not known with certainty by practitioners of the art. Three position‐dependent mechanisms of disruption were observed. Position dependence was probably due to focusing of the shock wave by an ellipsoidal reflector. Near the focus, the front surfaces of the test objects were roughed (spalated), probably by collapse of cavitation bubbles caused by passage of the shock wave. Also, midspecimen cleavage was seen, presumably caused by back wall reflection tensile stress. Distal to the focus back wall, spalation occurred, possibly due to tension caused by the expanding shock wave. Sieving fraction observations made of the effect of shock waves on “z brick” show that fragmentation has an approximate first‐order dependence on the number of shocks and a second‐order dependence on the voltage at which the shocks were generated. The multiphase character of the z brick was distinctly revealed in plots of percent fragmentation versus shock number; z brick is not a satisfactory test material, and there is a need for a well‐characterized set of test materials.
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Extracorporeal shock wave lithotripsy of gallstones: Objectives, current limitations, and preliminary in vitro and in vivo observations (A)

J. L. Thistle and B. T. Petersen

J. Acoust. Soc. Am. Volume 83, Issue S1, pp. S89-S89 (1988); (1 page)

Online Publication Date: 13 Aug 2005

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Surgical removal of gallstones is performed about 500 000 times per year in the United States. Although the usual cost ranges from $5000 to more than $10 000 per patient, the operative mortality is less than 1% for otherwise healthy persons. Nonsurgical dissolution of gallstones is often possible, but many gallstones contain calcium compounds that slow or prevent dissolution using the direct content cholesterol solvent, methyl tertbutyl ether (MTBE). Extracorporeal shock wave lithotripsy (ESL) has potential clinical utility for facilitating dissolution and possibly allowing spontaneous or induced passage of small fragments via the bile ducts and intestines. Obstacles to be overcome include predictable fragmentation of multiple stones up to 3 cm in diameter so that all particles are small enough to be rapidly dissolved or pass safely through the bile ducts (⩽ 3 mm). This must be achieved using biologically tolerable shock wave dosages without requiring general anesthesia within one or two treatment sessions. Acute and chronic safety, patient acceptance, and cost must be competitive with surgical treatment. Initial experience suggests that only solitary noncalcified stones (10% of patients with stones) have a high probability of success using ESL plus oral bile acid dissolution therapy. Improving ESL technology and direct contact fragment dissolution using MTBE should increase the clinical utility of shock wave lithotripsy of gallstones.
Contributed Papers
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Cavitation in flowing media by lithotripter shock waves in vitro and in vivo (A)

Douglas L. Miller, M. Delius, A. R. Williams, and W. Schwarze

J. Acoust. Soc. Am. Volume 83, Issue S1, pp. S89-S89 (1988); (1 page)

Online Publication Date: 13 Aug 2005

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Cavitation produced by lithotripter shock waves was characterized in vitro in water and blood, and in vivo in aortic blood by means of a resonant bubble detector. The 1.6‐MHz detector can detect and count 4 ± 1‐μm‐diam bubbles flowing through it by receiving their second harmonic emissions at 3.2 MHz. Spark‐gap lithotripters were used to expose the flowing liquid upstream of the detector at the shock wave focus. This system was readily able to detect bubbles resulting from shock wave‐induced cavitation in both water and blood flowing through plastic tubes in vitro, and even in blood pumped by the heart through a plastic arteriovenous shunt. Multiple (up to several hundred) bubble counts were obtained for each shock wave. However, for 200–400 shock wave exposures of each of two dogs, this system was unable to detect evidence of shock wave‐induced cavitational activity occurring within the intact vascular system in vivo. [Work supported by Dornier Medizintechnik and by NIH Grant CA 42947.]
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Cavitation processes induced by weak shock waves propagating in tissue (A)

H. Koch, M. Grünewald, and H. Hermeking

J. Acoust. Soc. Am. Volume 83, Issue S1, pp. S89-S89 (1988); (1 page)

Online Publication Date: 13 Aug 2005

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Human application of single‐cycle focused shock waves requires an intense study of the interaction processes associated with shock wave propagation in biological media. In this connection, shock wave‐induced cavitation processes on the scale of a single biological cell are of fundamental importance. On the basis of a model analysis including different propagation media for the bubble‐shock wave interaction and various shock wave profiles, possible hazards are discussed and compared with experimental and clinical results.
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Determination of design parameters for an ultrasonic kidney stone disintegrator (A)

R. Agarwal and V. R. Singh

J. Acoust. Soc. Am. Volume 83, Issue S1, pp. S89-S89 (1988); (1 page)

Online Publication Date: 13 Aug 2005

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Acoustic techniques are now increasingly used for the removal of kidney stones without surgery. In the past, generally, acoustic shock wave techniques and lithotripsy have been used. However, focused ultrasound may be used to disintegrate such stones, without any effect on the surrounding tissues. Ultrasonic characteristics of kidney stones are studied to determine further the design parameters such as modulus of elasticity, acoustic impedance, frequency of vibrations, etc., to develop a kidney stone disintegrator. The value of ultrasonic velocity in kidney stone in vitro is found to be almost double that of water or soft biological tissues.
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