Nanoparticle-mediated histotripsy (NMH) using perfluorohexane "nanocones"

: Nanoparticle-mediated histotripsy (NMH) is an ultrasound treatment strategy that combines acoustically sensitive nanoparticles with histotripsy. Previous NMH studies using perfluorocarbon (PFC) nanodroplets (ND's), ~200 nm in diameter, demonstrated that NMH can selectively generate cavitation by reducing the cavitation threshold from ~25-30 MPa to ~10-15 MPa. Recent studies have also shown that cavitation nucleation in NMH is directly caused by the incident negative pressure (p-) exposed to the PFC, as predicted by classical nucleation theory (CNT), suggesting that the NMH cavitation threshold is dependent on the total volume of PFC present in the focal region. In this study, we investigate the use of a newly developed NMH nanoparticle synthesized using an inclusion complex of methylated β-cyclodextrin and perfluorohexane (PFH). These 'nanocones' (NCs) have advantages compared to previously used ND's due to their smaller size (~50 nm), simple synthesis method, higher stability and information of definite PFH amount carried by the NC. To test the hypothesis that NCs can reduce the NMH cavitation threshold similar to ND's, and that the NMH cavitation threshold is dependent upon the total PFH concentration, tissue phantoms containing concentrations of NCs ranging from 10-5 to 10-10 (ml PFH/ml water) were exposed to single cycle ultrasound pulses using a 500 kHz focused transducer where high speed imaging captured cavitation data. Results showed that NCs significantly reduced the histotripsy cavitation threshold to 11.0 MPa for a concentration of 10-5 (ml PFH/ml water), with the threshold increasing at lower concentrations. Finally, the ability of NCs to be used for effective NMH ablation was demonstrated in tissue phantoms containing red blood cells (RBCs). Overall, the results of the study support our hypotheses that NCs can be used for effective NMH therapy and that NC concentration has a predictable threshold-reducing effect.