Lesion generation through ribs without aberration correction using cavitational therapy

Acoustic aberration from bones can cause significant decrease of peak focal pressure and induce the formation of secondary lobes in the focal profile. Thermal tissue ablation techniques require correction mechanisms when bones such as ribs are present in the acoustic window in order to reduce bone overheating and improve treatment accuracy. In this study we investigated the effects of rib obstruction in pulsed cavitational therapy, or histotripsy. To produce tissue fractionation using histotripsy, the initiation of a cavitation bubble cloud is required, which only occurs when the pressure is above a distinct threshold. We hypothesize that histotripsy can generate precise lesions even under aberration from rib bones, as long as the main beam retains its shape and is above the cavitation cloud initiation threshold while secondary lobes are below the threshold. To test this hypothesis, a 750 kHz, spherically focused transducer was used to generate 87 lesions in tissue-mimicking phantoms with and without rib aberration by a polycarbonate rib phantom and porcine rib sections placed between the transducer and its focus. All lesions were created by the application of 8000 pulses with 13–15 MPa peak rarefactional pressure at a pulse repetition frequency of 100 Hz. No aberration correction mechanisms were applied. A high-speed camera was used to observe bubble cloud formation and lesion development in the phantoms. Results showed that well-confined lesions were created in all cases, with comparable main lesion sizes and minimal collateral damage observed in lesions generated through the rib aberrators. These results support our hypothesis, suggesting that histotripsy can generate precise lesions through rib obstruction without requiring aberration correction mechanisms.