title: The importance of an expansion chamber during standard and tandem extracorporeal shock wave lithotripsy.
abstract: OBJECTIVE
  It is known that extracorporeal shock wave lithotripsy (SWL) may be improved by increasing cavitation using tandem shock waves. However, fluid is needed for the cavitation to work. The purpose of this research was to evaluate the importance of a fluid-filled expansion chamber in enhancing stone fragmentation during standard and tandem SWL.
  
  
  METHODS
  A piezoelectric lithotripter was modified to generate tandem shock waves. Artificial kidney stones inserted in vitro into the parenchyma of a pig kidney were exposed to either standard or tandem shock waves. Stones in one group were placed inside a small finger cot filled with water before they were introduced into the kidney. Stone fragments were strained through a mesh, dried, and weighed.
  
  
  RESULTS
  Water surrounding the stones always improved stone fragmentation. The best results were achieved using tandem shock waves at a delay of 250 micros.
  
  
  CONCLUSIONS
  A fluid-filled chamber surrounding the stone is essential for good SWL outcome. Tandem shock waves are more efficient than standard shock waves only if the stone is surrounded by fluid.
authors.affiliation: Departamento de Nanotecnología, Centro de Física Aplicada y Tecnología Avanzada, Universidad Nacional Autónoma de México, Querétaro, Qro., Mexico.
authors.forename: Francisco
authors.initials: F
authors.lastname: Fernández
authors.forename: Gilberto
authors.initials: G
authors.lastname: Fernández
authors.forename: Achim M
authors.initials: AM
authors.lastname: Loske