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

ABSTRACT BACKGROUND 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. METHODS 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) utilizing a custom enclosure for co-registered 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 utilizing a 50% duty cycle generating 11.9 MPa for 20, 30, 40, 50, and 60s. Experiments were repeated on ex vivo chicken livers in a water bath. Finally, the livers of 4 live swine underwent up to 6 CEUS-guided treatments using parameters optimized from in vitro work. RESULTS Treatment of the phantom between 20-60s, produced ablation sizes from 0.016 to 0.4 cm 3 . The relationship between time and size was exponential (R 2 = 0.992). Ablation areas were also well visualized on with ultrasound imaging. The ex vivo liver ablation size at 20s was 0.37 cm 3 , at 30s was 0.66 cm 3 , and at 100 s was 5.0 cm 3 . For the in-vivo swine experiments, the average ablation area measured 2.0x0.75 cm with a maximum of 3.5x1.5 cm. CEUS was utilized with the contrast agent Definity (Lantheus) for identification of lacerations as well as immediate post operative evaluation of therapy. CONCLUSION 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 grade III and IV liver laceration. STUDY TYPE Therapeutic/care management