Index of content:
Volume 103, Issue 6, June 1998
- BIOACOUSTICS 
103(1998); http://dx.doi.org/10.1121/1.423070View Description Hide Description
An ultrasound system has been developed to generate microbubblesin vivo for use as ultrasound contrast agent. Possible applications include diagnosis of reflux in the urinary tract. In experiments designed to elucidate the contrast microbubble generation process, acoustic bursts (at 1.8 MHz, 125 ms) were propagated through a latex rubber balloon, modeled after a rabbit urinary bladder, containing fluids of various air and carbon dioxide saturations and concentrations of cavitation nuclei (0.198-μm-diam polystyrene particles). The peak rarefactional pressure threshold for contrast microbubble generation, as visualized with a diagnostic ultrasound system, decreased approximately a factor of 2 for increasing particle concentration from to with the lowest threshold of 5.24 MPa. For samples with gas saturations below 50% and the average thresholds were at least twice as high as those of more saturated fluids (with mean threshold for saturated fluids of 6.45 MPa), and samples containing had considerably lower thresholds than respective under-saturations in air. At a fixed pressure amplitude, echogenicity tended to increase with both increasing particle concentration and gas saturation; this was more favorable for samples containing Even in a restricted-nuclei environment such as the urinary bladder, generation of vaporous cavitation should be possible; however, subsequently, abundant gas is needed to grow vaporous bubbles to persistent and imageable sizes, to assist in the diagnosis of urinary reflux.