In vivo evaluation of a MR-guided 980nm laser interstitial thermal therapy system for ablations in porcine liver

Purpose To evaluate the use of a 980-nm diode laser for magnetic resonance-guided laser interstitial thermal therapy (MR-guided LITT) ablations in liver tissue in an in vivo porcine model. Materials and methods MR-guided guided LITT was performed on nine juvenile pigs placed under general anesthesia. Target ablation sites were selected in the left and right lobes of the liver. Laser applicators were placed in the liver using intermittent MR guidance. Up to four separate ablations were performed in each animal using a 15 or 30 W laser generator using one or two applicators. During the ablations, continuous MR-based temperature mapping (MR-thermal mapping), using a proton resonance frequency technique, was performed to monitor the size of the ablation in real-time. Extent of thermal tissue damage was continuously estimated based on Arrhenius model. Two-minute ablations were performed at each site. MR-thermal mapping of ablations within the posteroinferior liver were accomplished with continuous breathing at low tidal volume. In the mid right lobe of the liver, due to motion artefacts, MR-thermometry was performed intermittently during breath hold periods. In the left lobe of the liver, ablations were performed with ventilation using positive end expiratory pressure (PEEP) of 10 cm of water. Upon completion, MR imaging with gadolinium contrast was performed to assess the extent of treatment. Thermal lesions were subsequently measured using both, MR-thermal dose and MR gadolinium images, for comparison. Following the animal euthanasia, the liver was harvested and subjected to formalin fixation and paraffin embedding for histological examination. Results Between one and four focal liver ablations (total 24 ablations) were successfully performed in nine animals with either a 15 or 30 W laser generator. For the 15-W laser generator, the average single applicator ablation size was (2.0 ± 0.5) × (2.6 ± 0.4) cm², as measured by magnetic resonance (MR) thermometry, or (1.7 ± 0.4) × (2.2 ± 0.6) cm ², as measured with gadolinium contrast, with the difference being not statistically significant. For the 30-W laser generator, the average single applicator ablation size was (2.4 ± 0.3) × (3.3 ± 0.5) cm² by MR thermometry and (2.1 ± 0.4) × (2.9 ± 0.3) cm² by gadolinium enhancement, with no statistically significant difference. Simultaneously activating two applicators with the 15 W generator demonstrated ablation sizes of (3.7 ± 0.9) × (3.2 ± 0.1) cm² using MR thermometry and (2.3 ± 0.6) × (2.4 ± 0.3) cm² with gadolinium contrast, while using two applicators in the 30-W laser generator, yielded (4.5 ± 0.6) × (3.9 ± 0.2) cm² using MR thermometry and (4.4 ± 1.1) × (3.6 ± 0.5) cm² with gadolinium contrast enhancement. Conclusion In our experience, we found that liver ablations performed with a MR-guided 980-nm diode LITT system through the saline cooled catheter applicator could be performed throughout the liver. Additionally, liver ablations were safe and produced a clinically applicable ablation zone. These results suggest the 980-nm diode laser MR-guided LITT system could be effective in treatments of hepatic tumors.