Development of a flexible endoscopic system using leached image guides for visible–near-infrared hyperspectral imaging

In this study, we propose a flexible endoscopic system using leached image guides compatible with visible–near-infrared (VIS–NIR) hyperspectral imaging (HSI) and evaluate its effectiveness through comparisons with a flexible endoscope using a silica-based bundle fiber. The proposed system employs a fiber structure based on leached image guides with an increased number of fibers (2,508) and high structural uniformity, together with a multilayer objective lens design that suppresses chromatic aberration from the visible to the near-infrared region. As a result, the wavelength-dependent focal adjustment using a liquid tunable lens and affine transformation for magnification correction, which were required in the conventional system, were eliminated, leading to a simplified data acquisition and preprocessing protocol. Functional evaluations confirmed significant improvements in fiber structural uniformity (standard deviation reduced from 32 to 4), an approximately 32% increase in spatial resolution, and a reduction in exposure time in the near-infrared range (900–1600 nm). In addition, the allowable bending radius was improved from 25 mm to less than 10 mm, providing high flexibility. Furthermore, in six-class resin identification experiments conducted as a performance evaluation metric, an average classification accuracy of 93.3% was achieved in the wavelength range of 1000–1600 nm, demonstrating that spectral discrimination performance is maintained in the improved flexible endoscope. Overall, the proposed VIS–NIR HSI-compatible flexible endoscopic system represents a promising device platform for applications not only in medical endoscopy but also in industrial inspection of confined or complex spaces.