The influence of ultrasound frequency and gas-body composition on the contrast agent-mediated enhancement of vascular bioeffects in mouse intestine

The induction by ultrasound (US) of petechiae and hemorrhages in mouse intestine was examined with injection of gas body-based contrast agents. Production of petechiae in the intestinal wall was enhanced by contrast agents for both continuous and pulsed (10 micros pulses repeated at 1 kHz) exposure relative to a gas body-free blank. For pulsed exposure with 10 mL/kg of Albunex, apparent thresholds for peak negative pressure amplitude were 0.42 MPa at 0.4 MHz, 0.85 MPa at 1.09 MHz and 2.3 MPa at 2.4 MHz. Results at these frequencies were the same for 10-11 cycle pulses with fixed duty cycle (0.01). Thresholds for hemorrhage into the intestinal lumen were not appreciably enhanced by added Albunex, and appear to be compatible with previously reported lithotripsy data when duty factor differences are considered. The agents PESDA, Optison and Levovist had lower thresholds (for example, 1.8 MPa for Levovist) than Albunex at 2.3 MHz, and yielded more petechiae. The thresholds for petechiae induction by US with contrast agents encroach upon the exposure range relevant to diagnostic US practice.