Development of a contrast-enhanced ultrasound-guided high-intensity focused ultrasound system for coagulation of liver parenchyma.

Abstract

The liver is the most common organ injured in blunt abdominal trauma and makes up roughly 5% of all trauma admissions. Current treatments are invasive and resource intensive, which may delay care. We aim to develop and validate a contrast-enhanced ultrasound (CEUS)-guided noninvasive tool to treat liver lacerations at the bedside. Two 1.8-MHz high-intensity focused ultrasound (HIFU) elements were coupled to a C1-6 diagnostic ultrasound probe and a Logiq E10 scanner (GE HealthCare, Waukesha, WI) using a custom enclosure for coregistered imaging and ablation. A phantom was created from polyacrylamide gel combined with thermochromic ink whose color changes above biological ablative temperatures (60°C). The HIFU wave was focused approximately 0.5 cm below the surface using a 50% duty cycle generating 11.9 MPa for 20, 30, 40, 50, and 60 seconds. Experiments were repeated on ex vivo chicken livers in a water bath. Finally, the livers of four live swine underwent up to six CEUS-guided treatments using parameters optimized from in vitro work. Treatment of the phantom between 20 and 60 seconds produced ablation sizes from 0.016 to 0.4 cm 3 . The relationship between time and size was exponential ( R2 = 0.992). Ablation areas were also well visualized on with ultrasound imaging. The ex vivo liver ablation size at 20 seconds was 0.37 cm 3 , at 30 seconds was 0.66 cm 3 , and at 100 seconds was 5.0 cm 3 . For the in vivo swine experiments, the average ablation area measured 2.0 × 0.75 cm with a maximum of 3.5 × 1.5 cm. Contrast-enhanced ultrasound was used with the contrast agent Definity (Lantheus Medical Imaging, North Billerica, MA) for identification of lacerations and immediate postoperative evaluation of therapy. These experiments demonstrate the feasibility of CEUS-guided transdermal HIFU ablation and the time-dependent size of ablation. This work warrants future investigations into using ultrasound to detect active bleeding and HIFU to coagulate grades III and IV liver laceration.