Shock wave pulse pressure after penetration of kidney tissue

Lithotripter generated compressional peak pressure (p⁺) was measured after penetrating tissue samples 0.5, 1, 2.5, and 4 cm thick. The samples were taken from fresh pig kidneys and insonated by shock wave pulses with positive peak pressures varying from 14 to 72 MPa. The measurement results allow one to draw some qualitative conclusions concerning the attenuation process in the lithotripter beam and show that in practice the compressional peak pressure values generated in the lithotripter may decrease almost by a factor of two before reaching the kidney stone. On the contrary, theoretical estimates indicate that negative pressures are practically not influenced by attenuation due to their different spectral composition     

The shadow behind a sphere immersed in water-measured, estimated, and computed

Acoustical pressure distribution behind a steel sphere 5 mm in diameter was measured in water for an incident plane wave with a 2.4-MHz frequency (ka=8pi). Measurements were carried out for continuous and pulse waves at various distance behind the sphere by means of a PVDF membrane hydrophone. The shadow range determined by measurements behind the steel sphere was about 15% shorter than estimated by means of formulae deduced earlier for a rigid sphere. The distributions of the acoustical pressure when measured and computed show almost the same shape. The obtained experimental results to a great extent agree with the theory for the rigid sphere elaborated for ka =4pi to 200 pi. Therefore, these formulae can be used as the first estimation of the shadow range behind an elastic steel sphere. The details of the measurement technique and possible reasons of differences between experiment and theory are discussed.