Spatially-offset optical coherence tomography (SO-OCT) for high dynamic range biological imaging at depth

Optical coherence tomography (OCT) in highly scattering media is limited by strong backscattering from superficial layers, which reduces sensitivity to weaker signals from deeper regions. Spatially-offset OCT (SO-OCT) addresses this limitation by introducing laterally displaced illumination and detection paths, thereby preferentially sampling photons originating from increased depths. Here, we demonstrate a high dynamic range imaging approach combining acquisitions at multiple spatial offsets and exposure times, using a tailored "weighted root-sum-square" merging algorithm. The resulting images exhibit enhanced contrast at depth without compromising structural fidelity in shallow regions. We achieve up to a tenfold improvement in contrast-to-noise ratio (CNR) in optical phantoms and a threefold improvement in ex vivo biological tissues compared to conventional OCT without any spatial offset. These results highlight the potential of SO-OCT combined with image merging to improve depth-resolved imaging and extend the practical dynamic range of OCT in biologically relevant scattering media.