Dual-frequency boiling histotripsy in an ex vivo bovine tendinopathy model

Histotripsy fractionates most soft tissues; however, healthy tendons have shown resistance to histotripsy fractionation. Prior work has shown that pre-heating tendons increases susceptibility to histotripsy fractionation; combining multiple driving frequencies may also allow successful fractionation of tendons. Here, we evaluate single- and dual-frequency histotripsy in four healthy and eight tendinopathic ex vivo bovine tendons. First, we evaluated single-frequency (1.07, 1.5, and 3.68 MHz) and dual-frequency (1.07 and 1.5MHz or 1.5 and 3.68 MHz) bubble dynamics with high-speed photography in a tissue-mimicking phantom. Then, tendons were treated with histotripsy. Cavitation activity was monitored with a passive cavitation detector (PCD) and targeted areas were evaluated grossly and histologically. Results in tendinopathic tendons showed 1.5 MHz or 3.68MHz single-frequency exposure caused focal disruption, whereas 1.5 and 3.68MHz dual-frequency exposures caused fractionated holes; all treatments caused some thermal denaturation. Exposure to 1.07 MHz alone or combined with 1.5MHz did not show fractionation in tendinopathic tendons. In healthy tendons, only thermal necrosis was observed for all tested exposures. PCD showed some differences in cavitation activity in tendinopathic tendons but did not predict successful fractionation. These results suggest that full histotripsy fractionation is possible using dual-frequency exposures in tendinopathic tendons. (c) 2023 Acoustical Society of America.

Automated summary

Histotripsy can fractionate most soft tissues, but healthy tendons have shown resistance. However, pre-heating tendons and using dual-frequency histotripsy may successfully fractionate tendons. This study evaluated the efficacy of single- and dual-frequency histotripsy in healthy and tendinopathic bovine tendons, and found that dual-frequency histotripsy can achieve complete fractionation in tendinopathic tendons.