Image-Guided Ultrasound Characterization of Volatile Sub-Micron Phase-Shift Droplets in the 20-40 MHz Frequency Range

Area of Science:

• Biomedical Engineering
• Acoustic Imaging
• Nanotechnology

Background:

• Phase-shift perfluorocarbon droplets offer potential as ultrasound contrast agents.
• Previous studies focused on lower ultrasonic frequencies (1-10 MHz), limiting application in small animal imaging.
• Higher frequencies (20-40 MHz) are crucial for preclinical ultrasound diagnostics.

Purpose of the Study:

• To characterize the vaporization of sub-micron decafluorobutane droplets at high ultrasound frequencies (20-40 MHz).
• To evaluate droplet performance in vitro and in vivo using standard B-mode imaging.
• To assess the impact of droplet size distribution on vaporization characteristics.

Main Methods:

• Utilized a preclinical ultrasound platform with standard B-mode imaging sequences.
• Investigated decafluorobutane droplet populations at center frequencies of 20, 30, and 40 MHz.
• Assessed droplet stability and vaporization thresholds under varying acoustic pressures.

Main Results:

• Droplets remained stable at low imaging pressures but vaporized at peak negative pressures around 3.5 MPa across tested frequencies.
• A small fraction of size outliers significantly affected droplet performance and vaporization assessment.
• Removing outliers enabled accurate vaporization threshold determination and produced microbubbles in vivo (mouse kidney).

Conclusions:

• High-frequency ultrasound (20-40 MHz) can effectively activate phase-shift perfluorocarbon droplets.
• Optimizing droplet size distribution is critical for reliable performance and accurate vaporization threshold determination.
• Vaporized droplets generate microbubbles suitable for preclinical ultrasound imaging applications.