Intraoperative Near-Infrared Fluorescence-Guided Peripheral Lung Tumor Localization in Rabbit Models

Background: A novel liposomal nanoparticle, CF800, that co-encapsulates indocyanine green for near-infrared (NIR) imaging and iohexol for computed tomography (CT) imaging has shown preferential tumor accumulation after intravenous injection by the enhanced permeability and retention effect. We hypothesized that CF800-enhanced NIR imaging would facilitate intraoperative localization of small lung nodules. Methods: A rabbit VX2 lung tumor model was implemented. CF800 was injected intravenously, followed by sequential CT acquisitions to track the biodistribution of CF800. Eleven rabbits were used for NIR fluorescence evaluation after thoracotomy at time points until 7 days after injection by using a NIR fluorescence thoracoscope in vivo. Organs of interests were removed for ex vivo analysis by using NIR imaging. Tumor-to-background (inflated lung) ratio was calculated and compared among the time points. Results: Both CT and NIR imaging indicated enhanced accumulation of CF800 within the VX2 tumor. NIR image analysis revealed the highest tumor-to-background ratio on days 4 and 5. High background at day 2 and low tumor signal at day 7 prevented distinct demarcation. Metastatic pulmonary small nodules (less than 2 mm in diameter) were successfully visualized by NIR imaging on day 4. However, NIR signal penetration was limited, resulting in localization failure for the few tumors deep (>0 mm) to the lung surface. Conclusions: NIR image-guided localization of small lung nodules appears to be feasible under certain conditions. However, further refinement will be required to increase tumor signal intensity and to reduce background signal from normal lung parenchyma, which is at least in part a consequence of persistent CF800 in the vasculature.