Mouse lung damage from exposure to 30 kHz ultrasound.

Two hundred and seventy mice were evaluated at three exposure durations (5, 10 and 20 min) and at six peak acoustic pressure levels (0, 65, 80, 87, 100 and 145 kPa) with 15 mice per exposure condition, at an ultrasonic frequency of 30 kHz modulated at 120 Hz. Threshold acoustic pressure levels for hemorrhage in mouse lung exposed for the three exposure durations appear to be in the range of 100 kPa. There did not appear to be a strong dependency on exposure duration. When compared to a study with mice in the megahertz frequency range (Child et al. 1990), it appeared that the threshold values followed a square root of frequency dependency, suggesting that the concept of the Mechanical Index (AIUM/NEMA, 1992), although developed for pulsed ultrasound conditions, may be extended to frequencies well below the diagnostic ultrasound frequency range.