INVITRO DETECTION OF CAVITATION INDUCED BY A DIAGNOSTIC ULTRASOUND SYSTEM

Experiments were performed in vitro to investigate the possibility of transient cavitation from short-pulse, diagnostic ultrasound under conditions comparable to clinical ultrasound examinations. An acoustic backscattering technique that utilizes 30-MHz pulsed ultrasound was employed to probe the potential of cavitation production by a clinical ultrasound scanner, specifically a Hewlett-Packard 77020A. Two calibrated, phased-array HP imaging transducers with 2.5- and 5.0-MHz operating frequencies were driven in M-mode (single cycle) and Doppler mode (4 cycles) by the HP imaging system. Hydrophobic polystyrene spheres with an average diameter of 0.245-mu-m and Albunex, an echo contrast agent consisting of 1- to 10-mu-m bubbles with a human serum albumen coating, served as potential cavitation nuclei. Cavitation was detected in the water with polystyrene spheres at 2.5 MHz in both M-mode and Doppler mode at a peak negative acoustic pressure of 1.1 MPa or greater. Insonification at 5.0 MHz in either mode did not produce a detectable amount of cavitation, even with peak negative pressures as high as 1.2 MPa. Also, cavitation was not detected in water with the Albunex spheres at either frequency.