Evaluation of an experimental electrohydraulic discharge device for extracorporeal shock wave lithotripsy: Pressure field of sparker array

Abstract

In this paper, an extracorporeal shock wave source composed of small ellipsoidal sparker units is described. The sparker units were arranged in an array designed to produce a coherent shock wave of sufficient strength to fracture kidney stones. The objective of this paper was to measure the acoustical output of this array of 18 individual sparker units and compare this array to commercial lithotripters. Representative waveforms acquired with a fiber-optic probe hydrophone at the geometric focus of the sparker array indicated that the sparker array produces a shock wave (P ∼40-47 MPa, P ∼2.5-5.0 MPa) similar to shock waves produced by a Dornier HM-3 or Dornier Compact S. The sparker array's pressure field map also appeared similar to the measurements from a HM-3 and Compact S. Compared to the HM-3, the electrohydraulic technology of the sparker array produced a more consistent SW pulse (shot-to-shot positive pressure value standard deviation of ±4.7 MPa vs ±3.3 MPa).

Preliminary Report on Stone Breakage and Lesion Size Produced by a New Extracorporeal Electrohydraulic (Sparker Array) Discharge Device

“…For the stones broken at the geometric focus of the SPA head, 71% (on average) of each stone was fractured to a size (< 2 mm) that is thought to pass out of the kidney without causing significant problems. Moving away from the focus (5 mm laterally off axis), which typically reduced peak SW pressures by 10 MPa, 7 reduced the ability to fracture the stones to 66%. Interestingly, placing the stones prefocal to the geometric focus (between the shock head and geometric focus) did not improve stone breakage.…”

“…Previous work has shown that this area is where both the peak positive pressure (is equal to pressure at the geometric focus) and peak negative pressure (is 25% greater than that produced at the geometric focus) are large. 7 Based on the data for the peak pressure locations it would be reasonable to predict that this region should be the best location for stone fracturing, since the stress on a stone would appear to be at a maximum. However, our results did not support this prediction.…”

“…Representative pressure waveform (averaged over 10 shots) when measured at the geometric focus (from Li et al). 7 The peak pressure of this waveform averaged 40 MPa. The positive pressure shock front and negative pressure tail appear similar (in shape and duration) to SW tracings produced by other extracorporeal shock wave lithotripters.…”

“…Details about the development and pressure field of the SPA can be found in Li et al 7 and in Supplementary Materials and Methods. Briefly, the SPA treatment head was designed to be mounted onto the frame of a Dornier Compact S lithotripter (Dornier MedTech, Kennesaw, GA) so that the x-ray C-arm of the Compact S could be used to target stones during the stone breakage tests, and to target the urinary collection system during evaluation of renal tissue injury.…”

Methods on the Determination of the Circuit Parameters in an Underwater Spark Discharge

“…e shock wave produced by an underwater spark discharge has been used in electrohydraulic forming [1], electrohydraulic cleaning [2], medical extracorporeal lithotripsy [3], rock breaking [4], marine geological exploration [5], underwater attack and defense [6], and so on. erefore, the characteristic of shock wave drew great attention to researchers.…”