Monitoring the coupling of the lithotripter therapy head with skin during routine shock wave lithotripsy with a surveillance camera.

ABSTRACT

PURPOSE: With lithotripters today the shock waves are typically transmitted into the body via water filled bellows using coupling gel to make contact with the skin. Usually the coupling zone is not visible to the operator. We investigated coupling quality during routine clinical shock wave lithotripsy and the associated effect on shock wave disintegration efficiency. MATERIALS AND METHODS: During 30 routine shock wave lithotripsy treatments the coupling zone was continuously monitored by a video camera integrated into a DoLi SII lithotripter (Dornier MedTech, Wessling, Germany). However, it was not shown to the blinded operator to resemble the standard clinical situation. We used 3 coupling gels, including LithoClear®, Sonogel® and a custom-made gel of low viscosity. The ratio of air in the relevant coupling area was measured. Lithotripter disintegration efficiency was evaluated by in vitro model stone tests at an air ratio of 0%, 5%, 10% and 20%. RESULTS: Only in 10 of 30 treatments was good coupling achieved with an air ratio of less than 5%. In 8 treatments the ratio was greater than 20%. The best coupling conditions were achieved with low viscosity gel. The mean ± SD number of shock waves needed for complete fragmentation in the model stone tests was 100 ± 4 for bubble-free coupling, and 126 ± 3 for 5%, 151 ± 8 for 10% and 287 ± 5 for 20% air bubbles. CONCLUSIONS: At 20 of 30 shock wave lithotripsy sessions there was imperfect coupling, accompanied by significant loss of disintegration capability. A surveillance camera is useful to monitor and improve coupling.