Safety and Efficacy of Histotripsy Treatments Near Implanted Metallic Fiducials and Endovascular Coils in Phantoms and in an In Vivo Swine Model

OBJECTIVE: This work evaluated the safety and efficacy of histotripsy treatments with metal in the therapeutic beam path or directly in the treatment zone. METHODS: Histotripsy treatments were performed on 66 agar phantoms with metal nearfield, adjacent to and within the treatment zone. Two endovascular coil sizes, a surgical clip and three gold fiducials were tested. The energy required to treat, treatment size and Dice coefficient were compared with control treatments without metal. In vivo histotripsy treatments were performed on four healthy swine (two treatments per animal). Treatments were performed centered on a metallic fiducial (n = 3) or deep to the endovascular coils (n = 3), as well as without metal in the beam path (control, n = 2). The control treatments were performed in independent areas of the liver. Imaging and gross necropsy were used to assess safety. Additionally, imaging and histology were used to assess efficacy. RESULTS: The phantom treatment energy levels, diameters and Dice coefficients, as well as in vivo treatment diameters, failed to show any significant differences between the experimental and control groups. No off-target damage was observed. Histologically, the treatment zones beneath a coil and over a metal fiducial were both complete, with acellular debris surrounded by a transition zone of hepatocytes with pyknotic nuclei and atrophic sinusoidal plates. CONCLUSION: Histotripsy with endovascular coils in the ultrasound beam path or with a metal fiducial directly in the treatment zone was safe and effective in this small, acute in vivo swine study.