CAREER: Dynamics of Holographic Acoustic Lenses for Nonlinear Ultrasound Focusing
Focused ultrasound (FU) is a transformative technology with the potential to treat many medical disorders noninvasively. Like using a convex lens to focus light beams on a single point, in FU, acoustic lenses are used to concentrate acoustic energy onto the desired target deep in the body. FU can be used to heat up, destroy, or change the target tissue, and has been projected as an effective tool for non-invasive brain tumor ablation, transient blood-brain barrier disruption, and neuromodulation, potentially leading to novel treatments of brain tumors, epilepsy, and Alzheimer’s and Parkinson’s diseases. However, in these applications, the inhomogeneous medium with non-flat geometry strongly attenuates, reflects, and distorts ultrasound waves, which could lead to inefficient and inaccurate delivery of acoustic energy. This Faculty Early Career Development Program (CAREER) project will enhance the state-of-the-art wave focusing capabilities by introducing a new generation of acoustic lenses capable of generating specified high-intensity FU fields. The lens design is based on characterizing the shape and acoustic properties of the target, imposing the desired acoustic field by a backward propagation model, calculating the unique thickness map of the lens design, and finally using a forward propagation model for reconstructing the target acoustic field. This research has the potential to lead the progress of science in emerging therapeutic applications of FU, enabling patient-specific medicine, where lenses are customized and 3D printed for each specific patient. Along with the research activities, the educational plan includes summer camps that will serve, mentor, and empower underrepresented students from historically black colleges and universities on the topic of ultrasound haptics using acoustic lenses. The student interns will acquire unique skills, build professional networks, and gain cross-cultural experiences.
The research introduces the concept of computer-generated holographic techniques to nonlinear acoustics. The experiments and modeling approaches aim to extend the capabilities of the acoustic holographic lenses to generate high-intensity scalable acoustic fields from a single element transducer. At higher excitation amplitudes, the nonlinear effects are exhibited by the generation of harmonics, distortion of the acoustic waveform, and possibly the formation of shock fronts. Such phenomena influence the pressure distribution and the diffraction pattern of the sound field. Therefore, new mix-domain algorithms that incorporate nonlinearities, for the forward and backward wave propagation, will be introduced to achieve efficient and precise patterning of high-intensity fields. The outcome of the research includes a mathematical framework for nonlinear wavefront shaping that advances the knowledge of inverse problems of nonlinear acoustics.