Marginal resection during resection of a spinal metastasis is frequently difficult because of the presence of important tissues such as the aorta, vena cava, and dura mater, including the spinal cord adjacent to the vertebral body. Thus, there is an urgent need for novel intraoperative imaging modalities with the ability to clearly identify bone metastasis. We have proposed a novel nanocarrier loaded with indocyanine green (ICG) (ICG-lactosome) with tumor selectivity attributable to its enhanced permeation and retention (EPR) effect. We studied its feasibility in intraoperative near-infrared (NIR) fluorescence diagnosis with ICG-lactosome for imaging spinal metastasis. A rat model of subcutaneous mammary tumor and a rat model of spinal metastasis of breast cancer were used. Fluorescence emitted by the subcutaneous tumors and the spinal metastasis were clearly detected for at least 24 h. Moreover, imaging of the dissected spine revealed clear fluorescence emitted by the metastatic lesion in the L6 vertebra while the normal bone lacked fluorescence. This study was the first report on NIR fluorescence imaging of spinal metastasis in vivo. NIR fluorescence imaging with ICG-lactosome could be an effective intraoperative imaging modality for detecting spinal metastasis.

Keywords: Animal study, indocyanine green, intraoperative imaging modality, nanocarrier, near-infrared fluorescence imaging, spinal metastasis..
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