Nanoparticle-mediated histotripsy using dual-frequency histotripsy pulsing: Comparison of bubble-cloud characteristics and ablation efficiency

Nanoparticle-mediated histotripsy (NMH) is a targeted ablation method using perfluorocarbon-filled nanoparticles to generate bubble-clouds at pressure levels (9–12 MPa) significantly below the histotripsy intrinsic threshold (>25 MPa). Prior studies have also shown a significant reduction in ablation efficiency compared to conventional histotripsy, likely from reduced bubble expansion and bubble-cloud density. Here, we investigate the bubble-cloud characteristics and ablation efficiency for NMH using dual-frequency pulsing. We hypothesize this method will increase ablation efficiency by increasing the bubble-cloud density and individual bubble expansion. High-speed optical imaging was used to characterize the cavitation threshold, cloud dimensions, and bubble-density of bubble clouds generated in agarose tissue phantoms, with and without perfluorohexane-filled nanocones, exposed to single-cycle dual-frequency pulses using a 500 kHz–3 MHz array transducer (1:1 pressure ratio). Ablation efficiency was investigated using red blood cell phantoms. Results showed dual-frequency NMH predictably produced smaller, denser, and more well-confined bubble-clouds and increased ablation efficiency compared to previous single-frequency studies, with complete ablation of the focal volume observed within 2000 pulses. This study demonstrates the potential of enhancing NMH ablation efficiency with dual-frequency pulsing and highlights the need for further studies to optimize NMH pulsing parameters for future clinical therapy development.