Abstract
Background
Intraoperative visualization of brain tumors with near-infrared (NIR)-fluorescent dyes is an emerging method for tumor margin approximation but are limited by existing fluorescence detection platforms. We previously showed that a dedicated NIR imaging platform outperformed a state-of-the-art neurosurgical microscope in fluorescence signal characteristics. This study examined whether conventional neurosurgical microscope NIR signal could be improved with the addition of a narrow wavelength excitation source.
Methods
Imaging was conducted with a broad-spectrum neurosurgical microscope and commercial near-infrared module. Addition of an 805-nm laser was used to “boost” NIR excitation of indocyanine green (ICG). In vitro quantification was performed on serial dilutions of ICG. Patients underwent tumor resection with delayed 24-h imaging of ICG infusion. NIR fluorescence of dura, cortex, or tumor was quantified from images prior to (pre-boost) and following added excitation with the laser (post-boost). Signal to background ratio (SBR) of pre- and post-boost was calculated as a readout of image enhancement.
Results
In vitro, excitation boost effected a 29% increase in mean SBR in six serial dilutions of ICG. Intraoperative boost was performed in 11 patients including meningioma, glioblastoma multiforme, and metastases. Increase in tumor fluorescence was pronounced under direct tumor visualization. Across all patients, boost excitation resulted in 35% mean improvement from pre-boost SBR (p < 0.001).
Conclusion
Neurosurgical microscopes remain the preferred method of visualizing tumor during intracranial surgery. However, current modalities for NIR signal detection are suboptimal. We demonstrate that augmentation of a fluorescence microscope module with a focused excitation source is a simple mechanism of improving NIR tumor visualization.
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Funding
Research reported in this publication was funded by the National Center for Advancing Translational Sciences of the National Institutes of Health under Award Number UL1TR001878. The content is solely the responsibility of the authors and does not necessarily represent the official views of the NIH. Additional financial support was received from the Institute for Translational Medicine and Therapeutics of the University of Pennsylvania. Funding sources had no role in the design or conduct of this research.
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All procedures performed in this study involving human participants were in accordance with the ethical standards of the institutional research committee of the Hospital of the University of Pennsylvania and with the 1964 Helsinki declaration and its later amendments or comparable ethical standards.
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Informed consent was obtained from all individual participants included in the study.
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This article is part of the Topical Collection on Brain Tumors
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• Digital Poster Presentation: Pennsylvania Neurosurgical Society’s (PNS) 105th Scientific Meeting, July 21, 2018 in Hershey, Pennsylvania
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Li, C., Buch, L., Cho, S. et al. Near-infrared intraoperative molecular imaging with conventional neurosurgical microscope can be improved with narrow band “boost” excitation. Acta Neurochir 161, 2311–2318 (2019). https://doi.org/10.1007/s00701-019-04054-5
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DOI: https://doi.org/10.1007/s00701-019-04054-5