In Vivo Thermal Ablation of Deep Intrahepatic Targets Using a Super-Convergent MRgHIFU Applicator and a Pseudo-Tumor Model

SIMPLE SUMMARY: Magnetic-resonance-guided high-intensity focused ultrasound (MRgHIFU) is a promising technology for ablation of liver tumors not eligible for surgery. This study aimed to demonstrate the workflow feasibility and the spatial accuracy of a novel concept of MRgHIFU transducer dedicated to deep intrahepatic targets on six in vivo pig livers. Before the MRgHIFU ablation, a histological marker mimicking a metastasis was defined in a region considered as challenging to resect. The pseudo-tumor, visible on pre-operative MR images and post-mortem gross pathology, was the target for validation of the entire workflow and the relevancy of the novel concept of HIFU transducer. The presence of the MRgHIFU ablations on gross pathology at the expected locations confirmed the ability to induce transcostal thermal lesions by MRgHIFU in challenging tumors. No relevant side effects on near-field tissues such as the skin or ribs were evidenced. ABSTRACT: Background: HIFU ablation of liver malignancies is particularly challenging due to respiratory motion, high tissue perfusion and the presence of the rib cage. Based on our previous development of a super-convergent phased-array transducer, we aimed to further investigate, in vivo, its applicability to deep intrahepatic targets. Methods: In a series of six pigs, a pseudo-tumor model was used as target, visible both on intra-operatory MRI and post-mortem gross pathology. The transcostal MRgHIFU ablation was prescribed coplanar with the pseudo-tumor, either axial or sagittal, but deliberately shifted 7 to 18 mm to the side. No specific means of protection of the ribs were implemented. Post-treatment MRI follow-up was performed at D7, followed by animal necropsy and gross pathology of the liver. Results: The pseudo-tumor was clearly identified on T1w MR imaging and subsequently allowed the MRgHIFU planning. The peak temperature at the focal point ranged from 58–87 °C. Gross pathology confirmed the presence of the pseudo-tumor and the well-delineated MRgHIFU ablation at the expected locations. Conclusions: The specific design of the transducer enabled a reliable workflow. It demonstrated a good safety profile for in vivo transcostal MRgHIFU ablation of deep-liver targets, graded as challenging for standard surgery.