High-Speed Imaging of Ultrasound-Mediated Bacterial Biofilm Disruption

Coupling Two Ultra-high-Speed Cameras to Elucidate Ultrasound Contrast-Mediated Imaging and Therapy

Ultrasound contrast-mediated medical imaging and therapy both rely on the dynamics of micron- and nanometer-sized ultrasound cavitation nuclei, such as phospholipid-coated microbubbles and phase-change droplets. Ultrasound cavitation nuclei respond non-linearly to ultrasound on a nanosecond time scale that necessitates the use of ultra-high-speed imaging to fully visualize these dynamics in detail. In this study, we developed an ultra-high-speed optical imaging system that can record up to 20 million frames per second (Mfps) by coupling two small-sized, commercially available, 10-Mfps cameras. The timing and reliability of the interleaved cameras needed to achieve 20 Mfps was validated using two synchronized light-emitting diode strobe lights. Once verified, ultrasound-activated microbubble responses were recorded and analyzed. A unique characteristic of this coupled system is its ability to be reconfigured to provide orthogonal observations at 10 Mfps. Acoustic droplet vaporization was imaged from two orthogonal views, by which the 3-D dynamics of the phase transition could be visualized. This optical imaging system provides the temporal resolution and experimental flexibility needed to further elucidate the dynamics of ultrasound cavitation nuclei to potentiate the clinical translation of ultrasound-mediated imaging and therapy developments.

Combined Confocal Microscope and Brandaris 128 Ultra-High-Speed Camera

Controlling microbubble-mediated drug delivery requires the underlying biological and physical mechanisms to be unraveled. To image both microbubble oscillation upon ultrasound insonification and the resulting cellular response, we developed an optical imaging system that can achieve the necessary nanosecond temporal and nanometer spatial resolutions. We coupled the Brandaris 128 ultra-high-speed camera (up to 25 million frames per second) to a custom-built Nikon A1R+ confocal microscope. The unique capabilities of this combined system are demonstrated with three experiments showing microbubble oscillation leading to either endothelial drug delivery, bacterial biofilm disruption, or structural changes in the microbubble coating. In conclusion, using this state-of-the-art optical imaging system, microbubble-mediated drug delivery can be studied with high temporal resolution to resolve microbubble oscillation and high spatial resolution and detector sensitivity to discern cellular response. Combining these two imaging technologies will substantially advance our knowledge on microbubble behavior and its role in drug delivery.