A feasibility study of an integrated NIR /gamma/visible imaging system for endoscopic sentinel lymph node mapping

Purpose The aim of this study is to integrate NIR , gamma, and visible imaging tools into a single endoscopic system to overcome the limitation of NIR using gamma imaging and to demonstrate the feasibility of endoscopic NIR /gamma/visible fusion imaging for sentinel lymph node ( SLN ) mapping with a small animal. Methods The endoscopic NIR /gamma/visible imaging system consists of a tungsten pinhole collimator, a plastic focusing lens, a BGO crystal (11 × 11 × 2 mm 3 ), a fiber‐optic taper (front = 11 × 11 mm 2 , end = 4 × 4 mm 2 ), a 122‐cm long endoscopic fiber bundle, an NIR emission filter, a relay lens, and a CCD camera. A custom‐made Derenzo‐like phantom filled with a mixture of 99m Tc and indocyanine green ( ICG ) was used to assess the spatial resolution of the NIR and gamma images. The ICG fluorophore was excited using a light‐emitting diode ( LED ) with an excitation filter (723–758 nm), and the emitted fluorescence photons were detected with an emission filter (780–820 nm) for a duration of 100 ms. Subsequently, the 99m Tc distribution in the phantom was imaged for 3 min. The feasibility of in vivo SLN mapping with a mouse was investigated by injecting a mixture of 99m Tc‐antimony sulfur colloid (12 MB q) and ICG (0.1 mL ) into the right paw of the mouse (C57/B6) subcutaneously. After one hour, NIR , gamma, and visible images were acquired sequentially. Subsequently, the dissected SLN was imaged in the same way as the in vivo SLN mapping. Results The NIR , gamma, and visible images of the Derenzo‐like phantom can be obtained with the proposed endoscopic imaging system. The NIR /gamma/visible fusion image of the SLN showed a good correlation among the NIR , gamma, and visible images both for the in vivo and ex vivo imaging. Conclusion We demonstrated the feasibility of the integrated NIR /gamma/visible imaging system using a single endoscopic fiber bundle. In future, we plan to investigate miniaturization of the endoscope head and simultaneous NIR /gamma/visible imaging with dichroic mirrors and three CCD cameras.