Contrast agent bubble and erythrocyte behavior in a 1.5-mhz standing ultrasound wave

Human erythrocytes and Optison contrastagent have been exposed to ultrasound, both alone and in combination, in a single-half-wavelength chamber driven at its resonance frequency (fo) of 1.5MHz. Cell movements were recorded by video microscopy at speeds up to 500 frames/s. The hypothesis that cells near astandingwave pressure node might be stressed by the microbubble products of sonicated contrastagent was examined. In the absence of contrastagent, cells moved rapidly to form an aggregate in the standingwave pressure node plane. First subharmonic and second harmonic emissions were detected from cell-contrastagent suspensions immediately on exposure to a threshold peak pressure amplitude of 0.98 MPa. Emissions at 3fo/2 occurred at 1.47 MPa, whereas white noise and lower-order subharmonic emissions coincided with the appearance of visible bubbles at a threshold of approximately 1.96 MPa. Cells exposed together with contrastagent at a pressure of 0.98 MPa precessed very rapidly about the pressure node plane. This behavior was discussed in the context of a recent analysis predicting that, in contrast to the situation for lower-pressure amplitudes, subresonant size bubbles translate about pressure node plane if the driving pressure amplitude is sufficiently high. Many precessing erythrocytes were clearly spiculated and this morphology persisted after the cells had left the area of precession. Hemoglobin release was significant under conditions inducing precession with first subharmonic and first harmonic emissions. Protein release increased discontinuously near the pressure thresholds, where more complex categories of frequency emission were detected. The potential of this system, which induces erythrocyte morphology changes and some protein release at the first emission threshold, to provide some control on the membrane-permeabilizing stress experienced by cells in a cavitation field is discussed