Development and clinical application of near-infrared surgical microscope: preliminary report

Visualization of near-infrared fluorescence through a surgical microscope can provide intraoperative information about deep-seated tissues. We studied the possibility of taking a near-infrared image through a surgical microscope after intravenous injection of indocyanine green (ICG). The surgical microscopes we used were Zeiss models OPMI MD and OPMI CS-NC. We used a halogen lamp as a light source, a band pass filter of 760 - 810 nm as an excitation filter, a laser light of 800 nm as an external light source, and a band pass filter of 820 - 920 nm as a barrier filter. Near-infrared fluorescence of vessels on the brain surface and of the dural sinus was visualized through the dura mater after intravenous injection of 25 mg ICG using a Hitachi KP-160 camera. Near-infrared fluorescence of vessels on the brain surface was observed through the dura mater. Venous images were clearer than were arterial ones. The dural sinus and the bridging veins were also clearly visualized. These results suggest that a clinical application of near-infrared fluorescence microscopy is possible. However, a stronger fluorescence emitted from ICG will be necessary for such a microscope to have practical use.