Biomedical subjects

Yuri A Pishchalnikov

Publications and source records attributed to Yuri A Pishchalnikov.

4 recordsLinked to original sources

PubMed2006

Detection of significant variation in acoustic output of an electromagnetic lithotriptor.

PURPOSE: We describe the observation of significant instability in the output of an electromagnetic lithotriptor. This instability had a form that was not detected by routine assessment, but rather was observed only by collecting many consecutive shock waves in nonstop regimen. MATERIALS AND METHODS: A Dornier DoLi-50 lithotriptor used exclusively for basic research was tested and approved by the regional technician. This assessment included hydrophone measures at select power levels with the collection of about 25 shock waves per setting. Subsequent laboratory characterization used a fiberoptic hydrophone and storage oscilloscope for data acquisition. Waveforms were collected nonstop for hundreds of pulses. RESULTS: Output was typically stable for greater than 1,000 shock waves but substantial fluctuations in acoustic pressures were also observed. For example, output at power level 3 (mean peak positive acoustic pressure +/- SD normally 44 +/- 2 MPa) increased dramatically to greater than 50 MPa or decreased significantly to approximately 30 MPa for hundreds of shock waves. The cause of instability was eventually traced to a faulty lithotriptor power supply. CONCLUSIONS: Instability in lithotriptor acoustic output can occur and it may not be detected by routine assessment. Collecting waveforms in a nonstop regimen dramatically increases sampling size, improving the detection of instability. Had the instability that we observed occurred during patient treatment, the energy delivered may well have exceeded the planned dose. Since the potential for adverse effects in lithotripsy increases as the dose is increased, it would be valuable to develop ways to better monitor the acoustic output of lithotriptors.

Acoustics↗

PubMed2006

Air pockets trapped during routine coupling in dry head lithotripsy can significantly decrease the delivery of shock wave energy.

PURPOSE: Current lithotriptors use a dry treatment head that must be coupled to the patient with gel or oil. We determined how the quality of coupling affects stone breakage under conditions that simulated patient treatment. MATERIALS AND METHODS: Experiments were performed with a Dornier (DoLi-50 electromagnetic lithotriptor. The test tank had a clear Mylar membrane for coupling with the treatment head water cushion. Thus, air pockets trapped at the coupling interface could be photographed for quantitation. Coupling efficiency was assessed using a fiberoptic hydrophone and different coupling regimes were tested for the effect on gypsum stone breakage. RESULTS: The quality of coupling was variable with air pockets covering 1.5% to 19% of the coupling area, resulting in a mean decrease in shock wave amplitude of approximately 20%. Breaking and reestablishing contact, as when a patient is repositioned during treatment, decreased acoustic pressure almost 32%, representing a 57% decrease in acoustic energy transmission. Stone breakage was also decreased when air was trapped in coupling and only 2% coverage by air pockets decreased stone breakage by 20% to 40%. CONCLUSIONS: These in vitro results suggest that coupling in lithotripsy can pose a significant barrier to the transmission of shock wave energy to the patient. Stone breakage was sensitive to air pockets at the coupling interface. Recoupling was particularly disruptive, suggesting that repositioning the patient could substantially degrade coupling quality. It seems reasonable that variability in the quality of coupling could contribute to variability in clinical outcomes.

Air↗

PubMed2006

Why stones break better at slow shockwave rates than at fast rates: in vitro study with a research electrohydraulic lithotripter.

BACKGROUND AND PURPOSE: Stones break better when the rate of shockwave (SW) delivery is slowed. It has been hypothesized that the greater cavitation accompanying a fast rate shields pulse propagation, thus interfering with the delivery of SW energy to the stone. We tested this idea by correlating waveforms measured at the SW focus with cavitation viewed using high-speed imaging. MATERIALS AND METHODS: A series of U30 gypsum stones held in a 2-mm mesh basket were exposed to 200 SWs at 30 or 120 SW/min from a research electrohydraulic lithotripter (HM3 clone). Waveforms were collected using a fiberoptic probe hydrophone. High-speed imaging was used to observe cavitation bubbles in the water and at the stone surface. RESULTS: Stone breakage was significantly better at 30 SW/min than at 120 SW/min. The rate had little effect on SW parameters in the water free field. In the presence of particulates released from stones, the positive pressure of the SW remained unaffected, but the trailing tensile phase of the pulse was significantly reduced at 120 SW/min. CONCLUSIONS: Cavitation bubbles do not persist between SWs. Thus, mature bubbles from one pulse do not interfere with the next pulse, even at 120 SW/min. However, cavitation nuclei carried by fine particles released from stones can persist between pulses. These nuclei have little effect on the compressive wave but seed cavitation under the influence of the tensile wave. Bubble growth draws energy from the negative-pressure phase of the SW, reducing its amplitude. This likely affects the dynamics of cavitation bubble clusters at the stone surface, reducing the effectiveness of bubble action in stone comminution.

Humans↗

PubMed2005

Cavitation detection during shock-wave lithotripsy.

A system was built to detect cavitation in pig kidney during shock-wave lithotripsy (SWL) with a Dornier HM3 lithotripter. Active detection using echo on B-mode ultrasound, and passive cavitation detection using coincident signals on confocal orthogonal receivers, were used to interrogate the renal collecting system (urine) and the kidney parenchyma (tissue). Cavitation was detected in urine immediately upon shock-wave (SW) administration in urine or urine plus X-ray contrast agent but, in native tissue, cavitation required hundreds of SWs to initiate. Localization of cavitation was confirmed by fluoroscopy, sonography and by thermally marking the kidney using the passive cavitation detection receivers as high-intensity focused ultrasound sources. Cavitation collapse times in tissue and native urine were about the same, but less than in urine after injection of X-ray contrast agent. The finding that cavitation occurs in kidney tissue is a critical step toward determining the mechanisms of tissue injury in SWL.

Animals↗