CIO 2022-24 Feasibility of Performing Hydrodissection During Renal Histotripsy: An In Vivo Porcine Study

Purpose: Histotripsy is an emerging non-invasive, non-ionizing, non-thermal focused ultrasound technique for treating abdominal tumors. Hydrodissection is commonly used to decrease the risk of non-target injury during thermal ablation by injecting fluid to displace nearby critical structures. Hydrodissection fluid is not degassed and may result in sub-optimal histotripsy treatment effects (e.g. near field cavitation). The objective of this study was to determine the safety and feasibility of performing hydrodissection during renal histotripsy in an in vivo porcine model.

Methods: Paired spherical histotripsy treatments (n=8 total, prescribed: 2 x 2 x 2 cm) were performed in the kidneys of ~50 kg domestic swine (n=4). In each animal, a control histotripsy was first performed without hydrodissection. In the contralateral kidney, ultrasound-guided hydrodissection was performed using contrast media-doped saline (2%) until the inferior pole of the kidney was surrounded by fluid (confirmed on cone-beam CT (CBCT)). A second histotripsy was then performed. A final contrast enhanced CBCT was acquired to assess treatment zones. A necropsy was performed, and the kidney and retroperitoneum were assessed for off target injury.

Results: Hydrodissection was successfully performed in all animals. The mean volume of hydrodissection fluid was 212.5 ± 65.0 mL and the mean distance from the hydrodissection fluid to the treatment zone was 0.75mm (range, 0-3mm). During histotripsy performed with hydrodissection, there was no evidence of near-field cavitation or off target effects on ultrasound. There was no statistically significant difference between the mean system drive voltage (34.8±5.9%, 36.7±3.9%, p=0.36), ablation zone volume (11.7 ± 4.6mL, 8.4±2.5mL, p=0.21), or ablation zone contrast-to-noise ratio (6.0±2.3, 4.7±0.8, p=0.34) of histotripsy treatments performed with or without hydrodissection, respectively. On imaging and necropsy, no major complications (hemorrhage, thrombus, off-target treatment effects, body wall injury) were noted either with or without hydrodissection.

Conclusion: There were no major differences found during the procedure, on imaging, or necropsy between histotripsy treatments performed with or without hydrodissection. These results suggest that histotripsy may be safely and effectively performed with the use of hydrodissection.