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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.

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.

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 …