Scattering anisotropy-weighted mesoscopic imaging

Abstract

We report that when tissue images are formed via a small solid angle in the backward direction (i.e., back-directional gating), the image intensity is dominantly determined by tissue scattering anisotropy. Thus, this configuration allows for scattering anisotropy-weighted imaging that can provide an intrinsic contrast by capturing tissue structures and organizations. To demonstrate the immediate feasibility, we apply scattering anisotropy-weighted imaging to tissue blocks including basal-cell carcinomas as a pilot study. The main feature of our imaging approach is the high sensitivity to tumor locations and the simplicity for large-area visualization. We further envision that scattering anisotropy-weighted imaging could potentially be used to visualize tissue microenvironments in a mesoscopic (between microscopic and macroscopic) imaging setting.

Fig. 1

Numerical experiments using optical ray-tracing combined with Monte-Carlo simulations. The number of photons detected by the virtual detector over different optical properties when the back-directional angle $\theta =25$ deg (a) and $\theta =5$ deg (b), corresponding to back-directional gating and conventional imaging setups, respectively. Surprisingly, when $\theta =5$ deg, the number of collected photons does not depend on $ls$ for a given $g$. Thus, the scattering intensity image obtained under back-directional gating can mainly be sensitive to changes in $g$.

Fig. 2

Representative cases of resected thick tissue blocks (thickness = 2 to 3 mm) with BCCs. $g$-weighted images are generated by summing the intensity within λ = 650 to 700 nm (a) and λ = 400 to 450 nm (b). Overall, $g$-weighted images at the low wavelengths show enhanced contrasts between tumor and nontumor areas, because the scattering intensity decreases over the wavelength in tissue. (c) Histology from the most adjacent thin frozen section ($\text{thickness}=5$ μm). Each histological image is generated by mosaicing $\sim 20$ low-resolution microscopy images and the locations of BCCs are circled. As indicated by the arrows, the larger tumor areas in the $g$-weighted images suggest that the residual tumors in the tissue blocks would be larger than those of the thin histological sections.