Generalized curved beam back-projection method for near-infrared imaging using banana function

Near-infrared imaging (NIRI) is a sub-surface imaging that makes a trade-off in recovery accuracy with depth of penetration. On the other hand, diffuse optical tomography (DOT) images tissue up to several centimeters. However, DOT reconstruction has a stability issue due to the inverse problem. This paper proposes a generalized continuous-wave technique to image objects of dimensions 4-6 cm comparable to DOT. A nonlinear Rosenbrock's banana function is fitted to the approximate photon path, and the fit parameter thus obtained gives the penetration depth of each channel. The calculated values of absorption change are back-projected along these curved paths for reconstruction without solving the inverse problem. This function serves as an operator for image reconstruction. Here numerical simulations, experimental validation on wax phantom with inclusions, finger joint, and degraded apple have been performed to show potential of the proposed method in imaging. Thus this computationally efficient, reliable, and simple method is suitable for practical and real-time NIRI applications.