Intra-operative HIFU treatment at the hepato-caval confluence of the liver in an in vivo porcine model

Abstract

Liver metastases located at the hepato-caval confluence are a main contra-indication for resection. A toroidal HIFU transducer was developed to intraoperatively treat liver metastases by creating fast and large ablations (up to 50 cm3in 6 minutes). This device is currently assessed in a clinical trial with 35 patients already included. This preclinical study evaluated, in an animal model, the feasibility and tolerance of an intraoperative HIFU treatment at the hepato- caval confluence before application to patients with metastases in that location. The diameter and the radius of curvature of the toroidal transducer were 70 mm focusing on a circle of 30 mm in diameter. The operating frequency was 2.5 MHz. The transducer was divided into 32 rings of equal surface for electronic focusing. An ultrasound imaging probe operating at 7.5 MHz was placed in the center of the HIFU transducer. Nine animals were treated and followed for 7 days after the HIFU procedure. Ultrasound Doppler images were recorded percutaneously and intraoperatively before and after treatment at day 0 and at day 7. HIFU exposure lasted 370 seconds using an acoustic power ranging from 80 W to 115 W. For each animal, the hepato-caval confluence of the left lateral lobe and the left medial lobe was targeted. Following gadolinium and heparin intravenous injection, liver was harvested and then imaged with a 3T MRI scanner. The HIFU ablations measured on average 27.5 ± 2.6 mm in diameter and 35.5 ± 6.8 mm long. All HIFU ablations were created around the targeted blood vessel (i.e. the hepato-caval confluence). The average diameter of the targeted vessels was 9.9 ± 1.0 mm. The HIFU lesion extended to the vessel wall while maintaining normal blood flow at day 7 as confirmed by Doppler images. No sign of thrombosis was observed on MRI nor at histological examination. Treatment was well tolerated over 7 days without any side effects. An intraoperative HIFU treatment of the liver at the hepato-caval confluence was shown to be safe and feasible using a toroidal HIFU transducer. Large and fast ablations were created while maintaining normal blood flow.