Photodisruptive laser nucleation of ultrasonic cavitation for biomedical applications

Pulses of high intensity laser light, when focused into transparent materia ls, may produce localized electron-ion plasmas through optical breakdown. B y simultaneously incorporating the resulting volume of vaporized material w ithin the focal volume of a high intensity ultrasound source, the photodisr uption (1.05 mum wavelength) void served as a nucleation site for ultrasoni c cavitation. Dilute suspensions of canine erythrocytes in phosphate buffer ed saline were exposed in a flow-through exposure chamber and the percentag e of lysed cells was used as a measure of the biologically effective cavita tion activity produced in the chamber. Brief (about 30 mus) acoustic emissi ons were detected from the photodisruption alone (indicating laser nucleati on of bubbles), but the cell lysis produced was undetectable against the ba ckground. However, combined exposure greatly increased both the duration of the acoustic emissions (up to 1.5 ms) and the amount of cell lysis above a n ultrasonic pressure amplitude threshold of about 4.3 MPa at 2.5 MHz. The amount of cell lysis (sometimes approaching 100%) increased with increasing ultrasonic intensity, laser pulse energy and laser PRF Addition of 5% seru m albumin enhanced the effect, apparently by stabilizing bubbles and nuclei . Photodisruptive laser nucleation of ultrasonic cavitation can provide con trolled and synergistic enhancement of bioeffects. (C) 2001 Society of Phot o-Optical Instrumentation Engineers.