Test for kidney hemorrhage following exposure to intense, pulsed ultrasound

A recent study has found that the threshold for extravasation in mouse kidney tissues by exposure to a spark-generated shock wave is of the order of 3-5 MPa (peak positive pressure). Since the mode pressure used by commercial pulsed Doppler ultrasound units is approximately 5 MPa, it is essential to determine whether these observations are relevant to diagnostic ultrasound. Hence, a comparable study has been completed using the same pathological endpoints but with exposure to pulsed ultrasound (10 microseconds pulse length) at 1.2 MHz and 3.8 MHz in which peak positive pressures exceeded 10 MPa. At these levels the focal waves are in shock because of the nonlinear properties of the propagating medium. The results of the pulsed ultrasound study were negative. Although this finding is encouraging for the use of diagnostic ultrasound, the two studies eventually must be integrated into a single mechanistic picture before the limits of safety will be known.