Li G et al, 2017: Evaluation of an experimental electrohydraulic discharge device for extracorporeal shock wave lithotripsy: Pressure field of sparker array.
Li G, Connors BA, Schaefer RB, Gallagher JJ, Evan AP.
School of Physics, Northeast Normal University, Changchun, 130024, People's Republic of China.
Department of Anatomy and Cell Biology, Indiana University School of Medicine, Medical Science Building, Room 0051, 635 Barnhill Drive, Indianapolis, Indiana 46202, USA.
Phoenix Science and Technology, C/O John Gallagher, 12 Van Buren Circle, Goffstown, New Hampshire 03045, USA.
Phoenix Science and Technology, 12 Van Buren Circle, Goffstown, New Hampshire 03045, USA.
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).
J Acoust Soc Am. 2017 Nov;142(5):3147. doi: 10.1121/1.5010901. FREE ARTICLE
The myth is alive! The legendary glory of the original HM3-Lithotripter outshines all succeeding lithotripter developments since its introduction in the early eighties. Its efficiency is deemed superior and unsurpassed since then. The recognized basis for this rating is the large focal zone in the range of 10-12 mm and the relative low pressure of e focus.
The presented design incorporates 27 small size ellipsoids with a diameter of 20.2mm and a focal distance of 181.6mm arranged on bowl-shaped spherical calotte. All single ellipsoids (sparker units) are aligned to face the same second focus at a distance of 181.6mm. The novelty of the design is the lack of a second electrode adjacent to the primary centre electrode. There is no spark-gap as in conventional EH systems. The surrounding liquid features an electric conductivity and provides by itself the second electrode required for sparking. Presumably, this technique should reduce wear of electrodes and increase lifetime of the device what needs to be proven.
Another interesting feature of the sparking device is the focus field. Pressure distribution in the focal area is similar to the HM3 and Dornier lithotripter Compact but slightly lower and significantly wider at the foot of the pressure profile. Due to relatively large primary energy (capacitors 490 nF and 21.6 kV vs 80nF and 18kV for HM3) spark generation of the original HM3 is more efficient. That is not relevant for clinical efficiency.
The wide focus of 13-15mm, however, is claimed to be of some value and comparable with the HM3.
The presented innovative approach intends to follow the tradition of the legendary HM3 and tries to add some improvements regarding more consistent shock wave delivery and electrode lifetime. The target results are partly realised by an extent of complexity of the device. This may be worth if the presumption of the superiority of a wide focus is right. Some technical targets are challenging. Due to the unavoidable jitter of some microseconds a coherent superposition of each pressure peak is difficult and, although one electrode is missing, a certain electrode wear is hard to avoid.
The solution compares to electro-magnetic and piezo-electric devices already in the market for decades featuring durability and low variability in shot-to-shot deviation. Only the focal zone may be a favourable feature if really the decisive factor for efficiency. This is still under debate. We are looking for further progress and finally, clinical results.