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AbstractHistotripsy is an emerging noninvasive, non-thermal, and non-ionizing focused ultrasound (US) therapy that can be used to destroy targeted tissue. Histotripsy has evolved from early laboratory prototypes to clinical systems which have been comprehensively evaluated in the preclinical environment to ensure safe translation to human use. This review summarizes the observations and results from preclinical histotripsy studies in the liver, kidney, and pancreas. Key findings from these studies include the ability to make a clinically relevant treatment zone in each organ with maintained collagenous architecture, potentially allowing treatments in areas not currently amenable to thermal ablation. Treatments across organ capsules have proven safe, including in anticoagulated models which may expand patients eligible for treatment or eliminate the risk associated with taking patients off anti-coagulation. Treatment zones are well-defined with imaging and rapidly resorb, which may allow improved evaluation of treatment zones for residual or recurrent tumor. Understanding the effects of histotripsy in animal models will help inform physicians adopting histotripsy for human clinical use.

Introduction This study was performed to determine the feasibility and safety of creating superficial histotripsy treatment in a live porcine thyroid model. Methods The porcine thymus comparable in size, shape and location to the human thyroid was used for this study. This model has been used for thyroid surgery studies due to the diminutive size of the porcine thyroid. Four female swine underwent a total of eight histotripsy treatments performed with a prototype therapy system (HistoSonics, Inc., Ann Arbor, MI). Two treatments were performed in each animal: a spherical 1.0 × 1.0 × 1.0 cm and ovoid 1.0 × 1.0 × 2.0 cm treatment zones. MRI immediately post-procedure was evaluated for histotripsy treatment zone size and imaging appearance, followed immediately by sacrifice. Tissue was then reviewed for percent cellular destruction and precision. Results Treatment zones measured on post treatment MRI were similar to prescribed volumes (spherical = 0.60 (+/− 0.11) cm3, ovoid = 1.23 (+/− 0.40) cm3, p > 0.05 vs. prescribed). MRI demonstrated well demarcated treatment zones and imaging findings consistent with cellular destruction. Histology demonstrated sharp transitions to normal tissue (mean 0.33 (+/− 0.13) cm), and high degrees of cellular destruction (mean 76% (+/− 12.5), range of 50–100%) in the treated tissue. Edema within the overlying muscle was seen in 2/8 treatments. Conclusion Histotripsy is capable of safely creating precise histotripsy treatments within the superficial neck of a porcine thyroid model without evidence of considerable complications.

Purpose The goal of this study was to compare intra-procedural radiofrequency (RF) and microwave ablation appearance on non-contrast CT (NCCT) and ultrasound to the zone of pathologic necrosis. Materials and methods Twenty-one 5-min ablations were performed in vivo in swine liver with (1) microwave at 140 W, (2) microwave at 70 W, or (3) RF at 200 W (n = 7 each). CT and US images were obtained simultaneously at 1, 3, and 5 min during ablation and 2, 5, and 10 min post-ablation. Each ablation was sectioned in the plane of the ultrasound image and underwent vital staining to delineate cellular necrosis. CT was reformatted to the same plane as the ultrasound transducer and transverse diameters of gas and hypoechoic/hypoattenuating zones at each time point were measured. CT, ultrasound and gross pathologic diameter measurements were compared using Student’s t-tests and linear regression. Results Visible gas and the hypoechoic zone on US images were more predictive of the pathologic ablation zone than on NCCT images (p