Intestinal hemorrhage produced by pulsed ultrasound or lithotripter fields

Abstract

The threshold for intestinal hemorrhage in mice was determined using a piezoelectric lithotripter. Mice were exposed to 200 lithotripter pulses with a PRF of ∼1 Hz. The amplitude of exposure was determined by either varying the position of the animal relative to the focus or by varying the voltage used to charge the lithotripter. Threshold for intestinal hemorrhage occurred at a peak acoustic pressure of 1–2 MPa. At threshold, the lithotripter waveform was nearly sinusoidal. Thresholds for intestinal hemorrhage were also determined for exposure to pulsed ultrasound at frequencies of 0.7, 1.1, 2.4, and 3.6 MHz. Intestines were exposed at 3–4 sites for 5 min per site using focused sources operating with a 10-μs pulse length and 100 Hz PRF. The threshold at 1.1 MHz was ∼1.5 MPa and thresholds increased with increasing frequency. Temperature rises of 1 –2 °C were measured in the intestine during exposure at the highest exposure conditions. Both the frequency dependence of intestinal hemorrhage and the limited heating are consistent with a cavitation mechanism of action.