Hemolysis in vivo from exposure to pulsed ultrasound

Ultrasonically induced hemolysis in vivo was studied when a commercial ultrasound contrast agent, Albunex®, was present in the blood. Murine hearts were exposed for 5 min at either 1.15 or 2.35 MHz with a pulse length of 10 μs and pulse repetition frequency of 100 Hz. During the exposure period, four boluses of Albunex® were injected into a tail vein for a total of ~ 0.1 mL of Albunex®. Following exposure, blood was collected by heart puncture and centrifuged, and the plasma was analyzed for hemoglo bin concentration. With Albunex® present in the blood, the threshold for hemolysis at 1.15 MHz was 3.0 ± 0.8 MPa (mean ± SD) peak positive pressure (~ 1.9 MPa negative pressure, ~ 180 W cm^-2 pulse average intensity). For the highest exposure levels (10 MPa peak positive pressure at the surface of the animal), the mean value for hemolysis was ~ 4% at 1.15 MHz and 0.46% at 2.35 MHz, i.e., the threshold at 2.35 MHz is > 10 MPa peak positive pressure. In contrast, hemolysis in control mice receiving saline injections at 10 MPa or sham-exposed (0 MPa) mice receiving Albunex® was ~ 0.4%.