Overpressurization System

One system for animal experiments is specifically designed to test for involvement of cavitation in biological effects caused by ultrasound. Whereas detection of cavitation using active or passive acoustic cavitation detectors can yield equivocal results, the use of overpressure to suppress cavitation activity provides definitive evidence of the role of cavitation. A significant change in the levels for effects at overpressure versus zero overpressure is a clear indication of cavitation involvement in the effects produced at atmospheric pressure, while no change is a clear indication that cavitation is not involved.

The system includes a stainless steel chamber that can be pressurized to at least 20 atmospheres (2 MPa) using compressed air. Previous studies have shown that an overpressure on the order of 10 atmospheres was sufficient to suppress cavitation in vivo (Lee and Frizzell, 1988). The chamber is wrapped with plastic tubing that provides temperature regulated water from a bath and this entire system is in turn wrapped with a fiberglass insulation layer. In addition, the water coupling medium placed in the chamber can be temperature controlled with a heating element, YSI proportional controller and stirrer. Brackets are included for mounting both transducers and animal holders in the chamber. The system can be used for exposure of neonatal and adult mice at frequencies from 200 kHz to 10 MHz and over a temperature range from 10-40C.

References

L.A. Frizzell, C. S. Lee, P. D. Aschenbach, M. J. Borrelli, R. S. Morimoto, and F. Dunn, "Involvement of Ultrasonically Induced Cavitation in the Production of Hind Limb Paraly-sis of the Mouse Neonate," J. Acoust. Soc. Am., 74: 1062-1065, 1983.

L.A. Frizzell and C. S. Lee, "Exposure Levels for Ultrasonic Cavitation in Mammals," Proc. Eighth Annual Conf. IEEE Eng. Med. Biol. Soc., Fort Worth, TX, Nov. 7-10, 1986, pp. 1026-1028.

C.S. Lee and L. A. Frizzell, "Exposure Levels for Ultrasonic Cavitation in the Mouse Neonate," Ultrasound Med. Biol., 14: 735-742, 1988.

L.A. Frizzell, E. Chen and C. Lee, "Effects of Pulsed Ultrasound on the Mouse Neonate: Hind Limb Paralysis and Lung Hemorrhage," Ultrasound Med. Biol., 20:53-63, 1994.