Ultrasound-induced fluid uptake phenomenon in porcine uterine tissue

Previous studies have shown that pulsed cavitational ultrasound therapy ("histotripsy") can mechanically fractionate many types of tissue. However, when uterine tissue was exposed to histotripsy pulses ex vivo, the tissue was observed to take up fluid from surrounding media without visual tissue damage. This paper is a quantitative study of this fluid uptake phenomenon and its association with acoustic cavitation. The endometrial surface of porcine uterine specimens were exposed to histotripsy pulses generated by a single-element 1.1 MHz transducer at a repetition frequency of 4 kHz, pulse duration of 10 cycles, peak rarefactional pressure (P^-) of 8.8-11.6 MPa, and exposure time of 25-100 seconds. The results showed that, at the highest pressure level, the amount of fluid reached a plateau after 50 seconds of ultrasound exposure, and the fluid uptake for 50 seconds exposure was quantified to be approximately a quarter (26.1±15.7%) of the specimen weight. In addition, in the association study with cavitation by varying pressure levels, this fluid uptake only occurred at P^(-) ≥ 9.7MPa when the initiation of the cavitation bubble cloud was detected by a passive monitoring transducer, and the cavitation activity indicated by acoustic backscatter increased with the fluid uptake. These results suggested that histotripsy can induce a large volume of fluid uptake in uterine tissue and this phenomenon is highly associated with cavitating bubble clouds activity. This fluid uptake phenomenon may have potential for drug delivery.