Cavitation mediated rat lung bioeffects from diagnostic ultrasound

Several animal models have exhibited petechial hemorrhage in the lung within the current FDA output limit of diagnostic ultrasound systems. To elucidate the mechanism of damage, seven rat lungs were simultaneously exposed or sham exposed in vivo to 6‐MHz pulsed Doppler ultrasound and interrogated with a confocally aligned 30‐MHz active cavitation detector (ACD) [R. A. Roy, S. Madanshetty, and R. E. Apfel, J. Acoust. Soc. Am. 20, 2451–2455 (1990)]. The right lung lobes of four 200 g rats were insonified with an ATL HDI 3000 6.0‐MHz Doppler pulse for 1.5 min and three rats were sham exposed. At the termination of ultrasound or sham exposure, each animal was immediately euthanized with sodium pentobarbital (200 mg/kg IP) and lung tissues were removed intact, inflated with buffered formalin, and examined by a pathologist who was blind to the exposure conditions. Histologically, damage was observed in the lungs exposed to ultrasound as extravasation of erythrocytes into the alveolar spaces. The ACD signal received was analyzed for the presence of increased scattering and radiated noise from inertial cavitation. The variance of the sequentially obtained ACD received pulses correlated with the damage in the exposed lungs. We conclude that inertial cavitation mediated the damage from diagnostic ultrasound.