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Effect of Contrast Agent on the Incidence and Magnitude of Ultrasound‐Induced Lung Hemorrhage in Rats

Objective: To test the hypothesis that inertial cavitation in the vasculature of the lung is not the physical mechanism responsible for ultrasound‐induced lung hemorrhage. Methods: A factorial design was used to study the effects of two types of injected agents (IA; 0.25 ml per rat of saline or Optison® given intravenously) and two levels of pulsed ultrasound exposure (UE; in situ peak rarefactional pressures of 2.74 and 5.86 MPa; respective mechanical indices of 1.02 and 2.14) on the incidence and size of lung lesions. Ten 10‐to‐11‐week‐old Sprague‐Dawley rats were exposed to pulsed ultrasound at each of the four combinations of IA and UE at a center frequency of 3.1 MHz, exposure duration of 10 s, pulse repetition frequency of 1,000 Hz and pulse duration of 1.2 μs. In addition, nine rats served as shams in which no lung hemorrhage occurred. Results: Rats administered contrast agent prior to exposure did not have an increase in lesion occurrence or size compared to rats that received saline with no contrast agent. Conclusions: These results provide further evidence that the mechanism for production of lung hemorrhage is not inertial cavitation. (ECHOCARDIOGRAPHY, Volume 21, July 2004)