Thresholds for transient cavitation produced by pulsed ultrasound in a controlled nuclei environment

Abstract

Transient cavitation is a discrete phenomenon that relies on the existence of stabilized nuclei, or pockets of gas within a host fluid, for its genesis. A convenient descriptor for assessing the likelihood of transient cavitation is the threshold pressure, or the minimum acoustic pressure necessary to initiate bubble growth and subsequent collapse. An automated experimental apparatus has been developed to determine thresholds for cavitation produced in a fluid by short tone bursts of ultrasound at 0.76, 0.99, and 2.30 MHz. A fluid jet was used to convect potential cavitation nuclei through the focal region of the insonifying transducer. Potential nuclei tested include 1-microns polystyrene spheres, microbubbles in the 1- to 10-microns range that are stabilized with human serum albumin, and whole blood constituents. Cavitation was detected by a passive acoustical technique that is sensitive to sound scattered from cavitation bubbles. Measurements of the transient cavitation threshold in water, in a fluid of higher viscosity, and in diluted whole blood are presented. These experimental measurements of cavitation thresholds elucidate the importance of ultrasound, host fluid, and nuclei parameters in determining these thresholds. These results are interpreted in the context of an approximate analytical theory for the prediction of the onset of cavitation.

Ultrasound with microbubbles enhances gene expression of plasmid DNA in the liver via intraportal delivery

“…For a free bubble comparable in size to an Optison MB, it is expected that violent inertial bubble collapse will have a threshold of B0.3-0.5 MPa at 1 MHz. 48 Thus the evidence is consistent with an IC-mediated phenomenon. However, unlike in vitro bioeffects or IC dose evolution, the data in Figure 6 suggest that there is an 'optimum,' or local peak response at 3 MPa.…”

HIFU for Palliative Treatment of Pancreatic Cancer

“…Thus, cavitation activity in tissue may occur if the amplitude of the rarefactional pressure exceeds a cer tain threshold, which in turn depends on ultrasound frequency with lower frequencies having lower rarefactional pressure thresholds. Cavitation threshold has been measured in different tissues in a number of studies, but there is still no agreement (21)(22)(23)28). For example, cavitation threshold in blood is estimated to be 6.5 MPa (23) at 1.2 MHz.…”

“…Microstreaming can produce high shear forces close to the bubble that can disrupt cell membranes and may play a role in ultrasound-enhanced drug or gene delivery when damage to the cell membrane is transient (28).…”

Cavitation Threshold of Microbubbles in Gel Tunnels by Focused Ultrasound

“…These studies cover a wide range of detection techniques, UCAs, equipment and US exposure conditions and are aimed at determining the thresholds for bubble collapse (Ammi et al 2006;Chen et al 2003a;Chen et al 2003b;Chien and Burns 2004;Chomas et al 2001a;Chomas et al 2001b;Crum et al 1992;Giesecke and Hynynen 2003;Holland and Apfel 1990;Shi et al 2000). In all of these investigations the microbubbles are usually placed in a vessel which is much larger than their sizes and therefore the effect of boundaries are negligible.…”