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To determine whether histotripsy can create human-scale transcostal ablations in porcine liver without causing severe thermal wall injuries along the beam path. Histotripsy was applied to the liver using a preclinical prototype robotic system through a transcostal window in six female swine. A 3.0 cm spherical ablation zone was prescribed. Duration of treatment (75 min) was longer than a prior subcostal treatment study (24 min, 15 s) to minimize beam path heating. Animals then underwent contrast-enhanced MRI, necropsy, and histopathology. Images and tissue were analyzed for ablation zone size, shape, completeness of necrosis, and off-target effects. Ablation zones demonstrated complete necrosis with no viable tissue remaining in 6/6 animals by histopathology. Ablation zone volume was close to prescribed (13.8 ± 1.8 cm3 vs. prescribed 14.1 cm3). Edema was noted in the body wall overlying the ablation on T2 MRI in 5/5 (one animal did not receive MRI), though there was no gross or histologic evidence of injury to the chest wall at necropsy. At gross inspection, lung discoloration in the right lower lobe was present in 5/6 animals (mean size: 1 × 2 × 4 cm) with alveolar hemorrhage, preservation of blood vessels and bronchioles, and minor injuries to pneumocytes noted at histology. Transcostal hepatic histotripsy ablation appears feasible, effective, and no severe injuries were identified in an acute porcine model when prolonged cooling time is added to minimize body wall heating.

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 To determine physician radiation exposure when using partial-angle computed tomography (CT) fluoroscopy (PACT) vs conventional full-rotation CT and whether there is an optimal tube/detector position at which physician dose is minimized. MATERIALS AND METHODS Physician radiation dose (entrance air kerma) was measured for full-rotation CT (360°) and PACT (240°) at all tube/detector positions using a human-mimicking phantom placed in a 64-channel multidetector CT. Parameters included 120 kV, 20- and 40-mm collimation, and 100 mA. The mean, standard deviation, and increase/decrease in physician dose compared with a full-rotation scan were reported. RESULTS Physician radiation exposure during CT fluoroscopy with PACT was highly dependent on the position of the tube/detector during scanning. The lowest PACT physician dose was when the physician was on the detector side (center view angle 116°; -35% decreased dose vs full-angle CT). The highest PACT physician dose was with the physician on the tube side (center view angle 298°; +34% increased dose vs full-angle CT), all doses P

BACKGROUND: Previous human-scale porcine liver model studies of histotripsy have resulted in ablation zones elongated in the cranial-caudal (CC) dimension due to uninterrupted respiratory motion during the ablation procedure. PURPOSE: The purpose of this study is to compensate for elongation of hepatic histotripsy ablation zones in the cranial-caudal (CC) dimension caused by respiratory motion by prescribing ellipsoid shaped ablations. METHODS: Six female swine underwent 12 hepatic histotripsy ablations using a prototype clinical histotripsy system under general anesthesia. Each animal received two ablation zones prescribed as either an ellipsoid (2.5cm (AP) x 2.5cm (ML) x 1.7cm (CC), prescribed volume=5.8cc) or a sphere (2.5cm all dimensions, prescribed volume 8.2cc). Ventilatory tidal volume was held constant at 400cc for all ablations. Post procedure MRI was followed by sacrifice and gross and microscopic histology. RESULTS: Ablations on MRI were slightly larger than prescribed in all dimensions. Ellipsoid plan ablations (2.8 × 3.0 × 3.1cm, volume 13.2cc, sphericity index 0.987) were closer to prescribed volume than spherical plan ablations (2.9 × 3.1 × 3.7cm, volume 17.1cc, sphericity index 0.953). Ellipsoid plan ablations were more spherical than sphere plan ablations, but the difference did not reach statistical significance (p=.06). Pathologic analysis confirmed complete necrosis within the center of each ablation zone with no widening of the zone of partial ablation on the superior and inferior as compared to the lateral borders (p=.22). CONCLUSION: Altering ablation zone prescription shape when performing hepatic histotripsy ablations can partially mitigate respiratory motion effects to achieve the desired ablation shape and volume.