Yuri A. Pishchalnikov

Cavitation selectively reduces the negative-pressure phase of lithotripter shock pulses.

Measurements using a fiber-optic probe hydrophone, high-speed camera, and B-mode ultrasound showed attenuation of the trailing negative-pressure phase of a lithotripter shock pulse under conditions that favor generation of cavitation bubbles, such as in water with a high content of dissolved gas or at high pulse repetition rate where more cavitation nuclei persisted between pulses. This cavitation-mediated attenuation of the acoustic pulse was also observed to increase with increasing amplitude of source discharge potential, such that the negative-pressure phase of the pulse can remain fixed in amplitude even with increasing source discharge potential.

Effect of firing rate on the performance of shock wave lithotriptors

To determine the mechanism that underlies the effect of shock wave (SW) rate on the performance of clinical lithotripters.

Independent assessment of a wide‐focus, low‐pressure electromagnetic lithotripter: absence of renal bioeffects in the pig

To assess the renal injury response in a pig model treated with a clinical dose of shock waves (SWs) delivered at a slow rate (27 SW/min) using a novel wide focal zone (18 mm), low acoustic pressure (<20 MPa) electromagnetic lithotripter (Xi Xin‐Eisenmenger, XX‐ES; Xi Xin Medical Instruments Co. Ltd., Suzhou, PRC).

Ultrasound-guided localized detection of cavitation during, lithotripsy in pig kidney in vivo

It is supposed that inertial cavitation plays a significant role in tissue damage during extracorporeal shock wave lithotripsy (ESWL). In this work we attempted to detect cavitation in tissue. In vivo experiments with pigs were conducted in a Dornier HM3 electrohydraulic lithotripter. Kidney alignment was made using fluoroscopy and B-mode ultrasound. Cavitation was detected by a dual passive cavitation detection (DPCD) system consisting of two confocal spherical bowl PZT transducers (1.15 MHz, focal length 10 cm, radius 10 cm). An ultrasound scanhead was placed between the transducers, an hyperechoic spots in the image indicated pockets of bubbles during ESWL. A coincidence-detection algorithm and the confocal transducers made it possible to localize cavitation to within a 4 mm diameter region. The signals from both the collecting system and kidney tissue were recorded. The targeting of the DPCD focus was confirmed by using the DPCD transducers as high intensity focused ultrasound (HIFU) sources at HIFU durations below the lesion formation threshold. In this HIFU regime, a bright spot appears in the B-mode image indicating the position of the DPCD focus. In this way we could confirm that refraction and scattering in tissue did not cause a misalignment. The tissue region interrogated was also marked with a lesion produced by HIFU. Clear cavitation signals were detected from the collecting system and from pools of blood that formed near the kidney capsule and weak signals were recorded from tissue during the ESWL treatment.

Evaluation of the LithoGold LG-380 Lithotripter: In Vitro Acoustic Characterization and Assessment of Renal Injury in the Pig Model

PURPOSE Conduct a laboratory evaluation of a novel low-pressure, broad focal zone electrohydraulic lithotripter (TRT LG-380). METHODS Mapping of the acoustic field of the LG-380, along with a Dornier HM3, a Storz Modulith SLX, and a XiXin CS2012 (XX-ES) lithotripter was performed using a fiberoptic hydrophone. A pig model was used to assess renal response to 3000 shockwaves (SW) administered by a multistep power ramping protocol at 60 SW/min, and when animals were treated at the maximum power setting at 120 SW/min. Injury to the kidney was assessed by quantitation of lesion size and routine measures of renal function. RESULTS SW amplitudes for the LG-380 ranged from (P(+)/P(-)) 7/-1.8 MPa at PL-1 to 21/-4 MPa at PL-11 while focal width measured ~20 mm, wider than the HM3 (8 mm), SLX (2.6 mm), or XX-ES (18 mm). For the LG-380, there was gradual narrowing of the focal width to ~10 mm after 5000 SWs, but this had negligible effect on breakage of model stones, because stones positioned at the periphery of the focal volume (10 mm off-axis) broke nearly as well as stones at the target point. Kidney injury measured less than 0.1% FRV (functional renal volume) for pigs treated using a gradual power ramping protocol at 60 SW/min and when SWs were delivered at maximum power at 120 SW/min. CONCLUSIONS The LG-380 exhibits the acoustic characteristics of a low-pressure, wide focal zone lithotripter and has the broadest focal width of any lithotripter yet reported. Although there was a gradual narrowing of focal width as the electrode aged, the efficiency of stone breakage was not affected. Because injury to the kidney was minimal when treatment followed either the recommended slow SW-rate multistep ramping protocol or when all SWs were delivered at fast SW-rate using maximum power, this appears to be a relatively safe lithotripter.

Evaluation of shock wave lithotripsy injury in the pig using a narrow focal zone lithotriptor.

Whats known on the subject? and What does the study add?

Size and location of defects at the coupling interface affect lithotripter performance.

Study Type – Therapy (case series)

Assessment of renal injury with a clinical dual head lithotriptor delivering 240 shock waves per minute.

PURPOSE Lithotriptors with 2 treatment heads deliver shock waves along separate paths. Firing 1 head and then the other in alternating mode has been suggested as a strategy to treat stones twice as rapidly as with conventional shock wave lithotripsy. Because the shock wave rate is known to have a role in shock wave lithotripsy induced injury, and given that treatment using 2 separate shock wave sources exposes more renal tissue to shock wave energy than treatment with a conventional lithotriptor, we assessed renal trauma in pigs following treatment at rapid rate (240 shock waves per minute and 120 shock waves per minute per head) using a Duet lithotriptor (Direx Medical Systems, Petach Tikva, Israel) fired in alternating mode. MATERIALS AND METHODS Eight adult female pigs (Hardin Farms, Danville, Indiana) each were treated with sham shock wave lithotripsy or 2,400 shock waves delivered in alternating mode (1,200 shock waves per head, 120 shock waves per minute per head and 240 shock waves per minute overall at a power level of 10) to the lower renal pole. Renal functional parameters, including glomerular filtration rate and effective renal plasma flow, were determined before and 1 hour after shock wave lithotripsy. The kidneys were perfusion fixed in situ and the hemorrhagic lesion was quantified as a percent of functional renal volume. RESULTS Shock wave treatment resulted in no significant change in renal function and the response was similar to the functional response seen in sham shock wave treated animals. In 6 pigs treated with alternating mode the renal lesion was small at a mean +/- SEM of 0.22% +/- 0.09% of functional renal volume. CONCLUSIONS Kidney tissue and function were minimally affected by a clinical dose of shock waves delivered in alternating mode (120 shock waves per minute per head and 240 shock waves per minute overall) with a Duet lithotriptor. These observations decrease concern that dual head lithotripsy at a rapid rate is inherently dangerous.

Bubble proliferation in the cavitation field of a shock wave lithotripter

Lithotripter shock waves (SWs) generated in non-degassed water at 0.5 and 2 Hz pulse repetition frequency (PRF) were characterized using a fiber-optic hydrophone. High-speed imaging captured the inertial growth-collapse-rebound cycle of cavitation bubbles, and continuous recording with a 60 fps camcorder was used to track bubble proliferation over successive SWs. Microbubbles that seeded the generation of bubble clouds formed by the breakup of cavitation jets and by bubble collapse following rebound. Microbubbles that persisted long enough served as cavitation nuclei for subsequent SWs, as such bubble clouds were enhanced at fast PRF. Visual tracking suggests that bubble clouds can originate from single bubbles.

Fragility of brushite stones in shock wave lithotripsy: absence of correlation with computerized tomography visible structure.

PURPOSE Brushite stones were imaged in vitro and then broken with shock wave lithotripsy to assess whether stone fragility correlates with internal stone structure visible on helical computerized tomography. MATERIALS AND METHODS A total of 52 brushite calculi were scanned by micro computerized tomography, weighed, hydrated and placed in a radiological phantom. Stones were scanned using a Philips® Brilliance iCT 256 system and images were evaluated for the visibility of internal structural features. The calculi were then treated with shock wave lithotripsy in vitro. The number of shock waves needed to break each stone to completion was recorded. RESULTS The number of shock waves needed to break each stone normalized to stone weight did not differ by HU value (p = 0.84) or by computerized tomography visible structures that could be identified consistently by all observers (p = 0.053). Stone fragility correlated highly with stone density and brushite content (each p <0.001). Calculi of almost pure brushite required the most shock waves to break. When all observations of computerized tomography visible structures were used for analysis by logistic fit, computerized tomography visible structure predicted increased stone fragility with an overall area under the ROC curve of 0.64. CONCLUSIONS The shock wave lithotripsy fragility of brushite stones did not correlate with internal structure discernible on helical computerized tomography. However, fragility did correlate with stone density and increasing brushite mineral content, consistent with clinical experience with patients with brushite calculi. Thus, current diagnostic computerized tomography technology does not provide a means to predict when brushite stones will break well using shock wave lithotripsy.