Measurement of shock wave properties after the passage through a tissue mimicking material

Extracorporeally generated ultrasonic shock waves are successfully used in lithotripsy to disintegrate kidney stones. Their physical parameters in the focus and their disintegration efficiency characterized by water tank measurements exhibit remarkable discrepancies to clinical experiences. To simulate and understand this clinical data we chose a liquid material (1,3 butanediol) in a polymer housing as a tissue phantom. This material coincides well with tissue for high amplitude applications in ultrasound speed, impedance, absorption, non-linearity parameter and reaction to acoustic cavitation. Inserting this tissue mimicking material in the pulse passage we measured the pressure parameters near the focus and their disintegration efficiency. The impact of the thickness of a 80 mm and a 50 mm material is negligible. More important is the distance between the absorbers exit window and the stone to be disintegrated. Close to the window the effect of this absorbing material is largest, but it decreases the more the distance behind the absorber is travelled by the again steepening shock wave