THE EFFECT OF POLYPROPYLENE VIALS ON LITHOTRIPTER SHOCK-WAVES

In studies to understand the mechanisms responsible for shock wave lit hotripsy (SWL) cell injury, we observed that shock waves (SWs) are inf luenced by the shape of the specimen vial, Lytic injury to kidney cell s treated in a Dornier HM3 lithotripter was higher (p < 0.0001) when S Ws entered the vial through the flat end (cap end) compared to the rou nd end, Measurements of the acoustic field within polypropylene vials were carried out using both lithotripter SWs and pulsed ultrasound (US ) in the megahertz frequency range, We compared pressure amplitudes in side the round and flat vials and found significant differences, When SWs entered through the round end, the average peak positive pressure was 40% of free-field pressure, due mostly to a dramatic reduction in pressure off axis, The average peak pressure inside the flat vial was twice that of the round vial, Experiments with US demonstrated that so und field focusing was induced by the curved interface of the round vi al, Ray analysis for the round vial indicates the presence of ''hot sp ots'' on axis and ''cold spots'' off axis, in qualitative agreement wi th pressure profiles, We conclude that the shape of the specimen vial is an important factor that should be considered in model systems of S WL cell injury. (C) 1997 World Federation for Ultrasound in Medicine & Biology.