Development of a contrast-enhanced ultrasound-guided high-intensity focused ultrasound system for coagulation of
Alexander Tam1, Kaizer Contreras, Fari Fall
1From the Sidney Kimmel Medical College (A.T.), Thomas Jefferson University, Philadelphia, Pennsylvania; Applied Physics Laboratory (K.C., A.M.), University of Washington, Seattle, Washington; Department of Surgery (F. Fall, G.K.), and Department of Radiology (J.-B.L., F. Forsberg, T.S.X., C.K.Y., J.R.E.), Thomas Jefferson University, Philadelphia, Pennsylvania; Department of Biomedical Engineering and Mechanics (E.V.), Virginia Polytechnic Institute and State University, Blacksburg, Virginia; and Department of Pathology (A.G.), Thomas Jefferson University, Philadelphia, Pennsylvania.
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, 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.
Results:
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.
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 grades III and IV liver laceration.
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