Digital refocusing for transverse resolution improvement in optical coherence tomography

Based on the fact that spectral domain (SD) optical coherence tomography (OCT) data can be treated as digital holography (DH) data acquired pointwise, we develop a spectral refocusing algorithm and show its ability to shift the focal region of OCT images obtained from SD OCT data acquired with a tightly focused scanning beam. Although refocusing itself depends on the refractive index of the studied media, we propose a procedure capable of restoring images with resolution equal to the resolution in the focal plane in the whole volume even in case of unknown refractive index of the media. As the proposed refocusing method operates with phases of the 3D Fourier spectrum of the SD OCT signal, it is very sensitive to the object motion during data acquisition. Thus, we also propose phase equalization preprocessing, which allows compensating the influence of such motions