Abstract: The use of ultrasound in medicine is widespread, ranging from imaging in OB/GYN to therapy, e.g., shock-wave lithotripsy for kidney stone treatment and histotripsy for pathogenic tissue ablation. In many of these procedures, pressure waves produce and/or interact with cavitation bubbles, whose dynamics and collapse may lead to tissue injury, unintentional or deliberate. This presentation summarizes our efforts to develop and use numerical modeling and high-fidelity simulations techniques to investigate cavitation dynamics in the context of ultrasound imaging (contrast-enhanced ultrasound) and therapy (lithotripsy and histotripsy). By considering simple model problems, we identify mechanisms responsible for certain key outcomes of ultrasound-induced cavitation. Numerical simulations of shock-bubble interaction demonstrate that the presence of individual cavitation bubbles amplifies the incoming pulse pressure in lithotripsy and produce sufficient tension to generate cavitation in histotripsy. Numerical modeling of spherical bubble dynamics in soft tissue shows that the viscoelasticity of the medium strongly affects the growth, frequency and energy dissipation of the bubble oscillations, and leads to previously unknown damage mechanisms. Using this model and experimental waveforms, bioeffects observed in contrast-enhanced ultrasound are correlated to the cavitation dynamics.
Bio: Eric Johnsen has been an Assistant Professor of Mechanical Engineering at the University of Michigan since 2010. He received his BS from UCSB in 2001, and MS and PhD from Caltech in 2002 and 2008, respectively. He then spent two years at Stanford as a post-doctoral fellow at the Center for Turbulence Research. His research interests lie in the broad field of fluid mechanics, including multiphase and compressible flow, CFD, turbulence and mixing, and plasmas. His group's work finds applications in biomedical engineering, energy, aeronautics and naval engineering. He is the recipient of the NSF CAREER Award (2013), ONR Young Investigator Award (2012) and the ORAU Ralph E. Powe Award (2010).