Spatially offset optical coherence tomography: enhancing image contrast at depth

Optical coherence tomography (OCT) is a powerful label-free approach for morphological imaging with numerous applications, especially within biomedicine. The penetration depth of OCT reaches well beyond conventional microscopy; however, signal reduction with depth leads to a rapid degradation of signal below the noise level, even with state-of-the-art detection schemes. Here, we demonstrate an original geometry for OCT that decouples the incident and collection light fields by introducing a spatial offset between them. This approach leads to a preferential collection of quasi-ballistic photons with depth, compensating for signal attenuation and enhancing the image contrast at depth. The effective signal attenuation can be reduced by over four times. Unseen features can be revealed with our approach, which we quantify using phantoms and samples of krill and zebrafish. A nine-fold enhancement in image contrast at depth in scattering biological samples. This facile and widely applicable geometry presents a major advance for label-free morphological imaging.