Sonoporation of monolayer cells by diagnostic ultrasound activation of contrast-agent gas bodies.

Human (A431 epidermoid carcinoma) cells were grown as monolayers on 5 microm thick Mylar sheets, which formed the upper window for a 1-mm thick, 23-mm diameter disc-shaped exposure chamber. A 3.5-MHz curved linear-array transducer was aimed upward at the chamber, 7 cm away, in a 37 degrees C water bath. The chamber contained phosphate-buffered saline (PBS) with 10 mg/mL fluorescent dextran and 1% Optison ultrasound (US) contrast agent. Significant fluorescent cell counts, indicative of membrane damage (i.e., sonoporation), up to about 10% of cells within a 1-mm diameter field of view, were noted for spectral Doppler and two-dimensional (2-D) scan mode with or without a tissue-mimicking phantom. The effect was only weakly dependent on pulse-repetition frequency or exposure duration, but was strongly dependent on contrast agent concentration below 2%. Thus, diagnostic US activation of contrast-agent gas bodies can produce cell membrane damage.