Tissue ablation using high-intensity focused ultrasound in the fetal sheep model: potential for fetal treatment

Objective The aim of this study was to investigate the efficacy of high-intensity focused ultrasound (HIFU) ablation of fetal tissue in a sheep model. HIFU can deliver large amounts of thermal energy by using ultrasonic waves to induce tissue necrosis, without damaging intervening tissues. In contrast to diagnostic ultrasound where intensity levels are below 0.1 W/cm2, HIFU can deliver 1,000 to 10,000 W/cm2 at the focal spot. Study design A protocol for HIFU-induced tissue coagulation in the fetus was developed in the ovine model. The fetal liver, lung, kidney, muscle, and placenta were targets for ultrasound-guided tissue ablation by a HIFU beam. All lesions were assessed macroscopically and by histologic analysis. Results In all animals, a necrotic lesion, similar in size to the HIFU focus (approximately 1×9 mm), was achieved. The fetal heart rate remained stable immediately after the procedure. Conclusion In conclusion, HIFU ablation seems to be an effective means to coagulate even highly vascularized tissues in the fetus. This procedure shows promise as a transcutaneous, minimally invasive technique to decrease blood flow through fetal tumors or vascular anastomoses. We are currently conducting further studies to refine the HIFU technique and assess safety for fetus and mother.