Reflection-mode optical diffraction tomography at 1.3 µm for deep tissue imaging

Visualizing subcellular structures in thick biological tissues in vivo demands advanced imaging techniques that combine high spatial resolution and deep penetration depth. While several optical methods can achieve millimeter-scale imaging depths, their spatial resolution is largely insufficient for resolving subcellular features and often lacks quantitative physical information. Optical diffraction tomography (ODT), as a label-free volumetric imaging technique, maps the refractive index tomograms of biological samples that contain rich biophysical information. However, conventional visible-light ODT systems are mostly limited to imaging depths below 100 μm, which is insufficient for in vivo imaging that suffer from strong tissue scattering and absorption. To overcome these challenges, we propose a novel ODT technique using 1.3 μm illumination for deep-tissue imaging. To enhance the lateral resolution and depth selectivity, we employ dynamic speckle illumination with vortex beams. By modeling the three-dimensional (3D) coherent transfer function and 3D point spread function, it is found that lateral/axial resolutions of 600 nm/1.1 μm and a depth selectivity of 0.8 μm can be achieved. Our preliminary experimental results have demonstrated high-contrast phase imaging of microparticles embedded > 200 μm within turbid media mimicking the brain cortex attenuation.