Near-Infrared Transillumination for Macroscopic Functional Imaging of Animal Bodies

SIMPLE SUMMARY: Advancements in optical technology have revitalized transillumination imaging for biomedical research. Using near-infrared (NIR) light, we have visualized internal structures in animals, even under conditions of heavy optical scattering. By extending the Beer–Lambert law’s applicability through differentiation principles, we can observe real-time physiological changes noninvasively. A hurdle in transillumination is image blurring caused by scattering in body tissues. We have addressed this difficulty by extracting near-axis scattered components from diffuse light, and by employing software techniques such as PSF deconvolution and deep learning. This shift has enabled the clear 3D imaging of internal structures from blurred 2D images. Validation through experimentation with human and animal subjects has underscored the effectiveness of these techniques. Integrating transillumination with modern technology holds great promise for future biomedical applications. ABSTRACT: The classical transillumination technique has been revitalized through recent advancements in optical technology, enhancing its applicability in the realm of biomedical research. With a new perspective on near-axis scattered light, we have harnessed near-infrared (NIR) light to visualize intricate internal light-absorbing structures within animal bodies. By leveraging the principle of differentiation, we have extended the applicability of the Beer–Lambert law even in cases of scattering-dominant media, such as animal body tissues. This approach facilitates the visualization of dynamic physiological changes occurring within animal bodies, thereby enabling noninvasive, real-time imaging of macroscopic functionality in vivo. An important challenge inherent to transillumination imaging lies in the image blur caused by pronounced light scattering within body tissues. By extracting near-axis scattered components from the predominant diffusely scattered light, we have achieved cross-sectional imaging of animal bodies. Furthermore, we have introduced software-based techniques encompassing deconvolution using the point spread function and the application of deep learning principles to counteract the scattering effect. Finally, transillumination imaging has been elevated from two-dimensional to three-dimensional imaging. The effectiveness and applicability of these proposed techniques have been validated through comprehensive simulations and experiments involving human and animal subjects. As demonstrated through these studies, transillumination imaging coupled with emerging technologies offers a promising avenue for future biomedical applications.