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 mm3), a fiber‐optic taper (front = 11 × 11 mm2, end = 4 × 4 mm2), 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 99mTc 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 99mTc 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 99mTc‐antimony sulfur colloid (12 MBq) 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.