A new sonoablation using acoustic droplet vaporization and focused ultrasound: A feasibility study

Background: Histotripsy and boiling histotripsy are two methods of mechanical ablation that use high-pressure focused ultrasound (FUS). Purpose: Here, a new bubble sonoablation technique was investigated using low-pressure FUS in combination with local injection of perfluoropentane (PFP) in rabbit liver. Methods: Fifteen healthy New Zealand white rabbits were treated with FUS alone, FUS + PFP or PFP alone. FUS was performed using a single-element focused transducer (frequency 596 kHz, 0.27 ms pulses, 0.54% duty cycle, and peak negative pressure 2.0 MPa). Ten minutes before FUS treatment, the PFP droplet was locally injected into the rabbit liver, where the ultrasound was focused. Contrast-enhanced ultrasound (CEUS) of the liver was performed, and the temperature at the liver surface in the targeted liver region was recorded during treatment. The livers were collected for pathological examination. Statistical significance was set at p < 0.05. Paired t-tests were used to compare the pre- and post-treatment values. One-way analysis of variance was performed to compare multiple groups, and the least significant difference method was used for further comparisons between the two groups. Results: Analysis of CEUS data showed that the values of area under the curve (AUC) were significantly different in the PFP + FUS group pre(10453.644 +/- 1182.93) and post-treatment (4058.098 +/- 2720.41), and the AUC values of PFP + FUS post-treatment (4058.098 +/- 2720.41) were also significantly lower than those of the FUS (9946.694 +/- 1071.54) and the PFP (10364.794 +/- 2181.53) groups. The peak intensity values also showed the same results, the value of peak intensity of PFP+FUS post-treatment was 82.958 +/- 13.99, whereas there was no difference between FUS (106.61 +/- 7.61) and PFP (104.136 +/- 10.55). Hematoxylin and eosin (H&E) staining revealed that the pathological damage ratings of the PFP + FUS, PFP, and FUS groups were grade 3, grade 1, and grade 0, respectively. Specifically, the area of liver necrosis in the PFP + FUS group (0.99 +/- 0.29 cm2) was 198 times higher than that in the PFP group (0.005 +/- 0.008 cm2), whereas no necrosis was observed in the livers treated with FUS alone. Simultaneously, the number of vacuoles in the liver of the PFP + FUS group (35.50 +/- 23.31) was approximately five times that of the PFP group (7.00 +/- 12.88), whereas no vacuoles were found in the liver treated with FUS alone. Conclusion: PFP droplets combined with FUS can destroy liver tissue and cause tissue necrosis in the droplet injection area, without affecting the structure of surrounding tissue.