Electrowetting-driven liquid lens for ultrasound: Enabling controllable focal length and flexible beam steering.

Focused ultrasound is an increasingly popular non-invasive treatment modality. Still, its fixed focal point requires an array ultrasound transducer or scanning system to cover different therapeutic scenarios. To address this limitation, we developed an electrically-controlled liquid lens that enables dynamic beam focusing and steering of the incident plane ultrasound beam. The lens was carefully optimized for low-energy attenuation and low-voltage driving. We evaluated the performance of the lens using a homemade 5.5-MHz planar transducer with a 7.5-mm aperture. Our results demonstrate that the planar ultrasound beam can be adjusted to a focused beam with a focal length from 27 mm to 32 mm within 1 s by increasing the electric input (0-60 V) to the lens. Additionally, the beam angle of the ultrasound is tunable from -5 to 5° by adjusting the charge distribution on the lens. Our design enables real-time, fast-response, on-demand changing of focal length and beam angle for a single-element planar transducer. Our study presents a promising technology for altering the ultrasound beam of a planar single-element transducer for different ultrasound applications. The development of this electrically-controlled liquid lens has the potential to enhance the efficacy of focused ultrasound treatment and improve patient outcomes.

Improvement of light penetration in biological tissue using an ultrasound-induced heating tunnel.

The major obstacles of optical imaging and photothermal therapy in biomedical applications is the strong scattering of light within biological tissues resulting in light defocusing and limited penetration. In this study, we propose high intensity focused ultrasound (HIFU)-induced heating tunnel to reduce the photon scattering. To verify our idea, Monte Carlo simulation and intralipid-phantom experiments were conducted. The results show that the thermal effect created by HIFU could improve the light fluence at the targeted region by 3% in both simulation and phantom experiments. Owing to the fluence increase, similar results can also be found in the photoacoustic experiments. In conclusion, our proposed method shows a noninvasive way to increase the light delivery efficiency in turbid medium. It is expected that our finding has a potential for improving the focal light delivery in photoacoustic imaging and photothermal therapy.

Thermal-sensitive acoustic droplets for dual-mode ultrasound imaging and drug delivery.

Mild hyperthermia (40-43 °C) could assist with acoustic droplet vaporization (ADV) via focused ultrasound heating and enable ultrasound thermal imaging to monitor the heating position. We explored the possibility of predicting the treatment position of ADV using thermal-sensitive droplets (TSDs) and ultrasound thermal imaging. The TSDs were created with an encapsulated mixture of C5F12 and C6F14 that could be vaporized by ultrasound under mild hyperthermia. The ultrasound imaging-guided high-intensity focused ultrasound system was used to collect ultrasound images, heat tumors, and vaporize the TSDs. The overlap between the location of heating and ADV-induced bubble formation was used to evaluate the accuracy of predicting the treatment position. The optimal fabrication of TSDs (1.21 ±â€¯0.19 µm, volume ratio of C5F12:C6F14 = 7:3) increased ADV efficiency by 33 ±â€¯11% at 41 °C under an acoustic pressure of 8.6 MPa. The accuracy of ADV region prediction by ultrasound thermal imaging was 87.2 ±â€¯3.5% for the in vitro study and 83.2 ±â€¯8.6% for the in vivo study. The similarity among the location of bubble enhancement and distribution of 41 °C areas demonstrated the credibility of our estimates. Therefore, in this study, we validated the feasibility of applying TSDs and ultrasound thermal imaging to predict the in vivo treatment position of ADV.