Computational augmentation of spatially coherent full-field optical coherence microscope for cellular-resolution and millimeter-depth imaging

Optical coherence tomography (OCT) microscope (OCM) uses the high numerical aperture (NA) objective to achieve cellular-level lateral resolution. However, its practical imaging depth range is limited by the depth of focus (DOF). And hence, high-resolution OCM has not been a true volumetric imaging modality. Although computational refocusing methods can potentially provide sharp images outside the DOF, signal intensity reduction by the confocal pinhole (i.e., the single-mode fiber tip of point scanning OCT) still limits the imaging depth in practice. In addition, the OCT cannot visualize intra-tissue activities. To overcome these limitations, we demonstrated the spatially coherent full-field OCM (SC-FFOCM) hardware with computational signal processing. The in-focus lateral resolution is 1.7μm, and the axial resolution is 6.5μm (in air). The lateral field-of-view is 0.43 × 0.37mm2, and the volumetric acquisition speed is 4 volumes per second. Although a 2.3mm depth field is acquired, the DOF is very short as 5.5μm. Post-acquisition extension of the imaging depth is performed by computational refocusing with a phase-only spatial frequency filter. Notably, since SC-FFOCM does not have a confocal pinhole, this refocusing enables sharp and high signal-to-noise ratio (SNR) imaging across the 2.3mm depth field. In addition, the repetitive volume acquisition protocol was designed to visualize intra-tissue activities (i.e., Dynamic OCT imaging). Human breast adenocarcinoma (MCF-7 cell line) spheroids were examined. It was demonstrated that cellular-level volumetric imaging is obtained over the full depth of the spheroid (around 0.35mm) with high SNR and intra-tissue activity is visualized.