Accessing depth-resolved high spatial frequency content from the optical coherence tomography signal

Abstract

Optical coherence tomography (OCT) is a rapidly evolving technology with a broad range of applications, including biomedical imaging and diagnosis. Conventional intensity-based OCT provides depth-resolved imaging with a typical resolution and sensitivity to structural alterations of about 5–10 microns. It would be desirable for functional biological imaging to detect smaller features in tissues due to the nature of pathological processes. In this article, we perform the analysis of the spatial frequency content of the OCT signal based on scattering theory. We demonstrate that the OCT signal, even at limited spectral bandwidth, contains information about high spatial frequencies present in the object which relates to the small, sub-wavelength size structures. Experimental single frame imaging of phantoms with well-known sub-micron internal structures confirms the theory. Examples of visualization of the nanoscale structural changes within mesenchymal stem cells (MSC), which are invisible using conventional OCT, are also shown. Presented results provide a theoretical and experimental basis for the extraction of high spatial frequency information to substantially improve the sensitivity of OCT to structural alterations at clinically relevant depths.

Skin cancer margin detection using nanosensitive optical coherence tomography and a comparative study with confocal microscopy

“…All post-processing steps were done separately in MATLAB after data acquisition to reconstruct conventional B-scan images and nanosensitive OCT (nsOCT) images. In the previous studies [ 42 , 42 , 46 ] we used commercial SDOCT system (Telesto III, Thorlabs.inc) with centered at 1300 nm (bandwidth 237 nm, wavelength range 1176-1413 nm).…”

“…Nanosensitive OCT (nsOCT) is a novel imaging technique based on the spectral encoding of spatial frequencies (SESF) principle which was used for real-time and super-resolution imaging [ 33 – 38 ]. The nsOCT technique visualizes sub-wavelength structure without resolving it and provides nanoscale sensitivity to structural changes from single frame [ 39 – 44 , 46 ]. An advantage of this technique has been its use for real-time and super-resolution imaging [ 37 , 38 ].…”

“…Each local frequency component of the scattering object is encoded in a corresponding optical illumination wavelength range. Recently, nsOCT has been applied to detect both structural [ 42 – 44 ] and functional [ 45 ] changes in ex vivo and in vivo biological tissues including visualization of the nanoscale structural changes within mesenchymal stem cells (MSC) [ 46 ]. The nsOCT gives the information content of the FDOCT signal which is based on the general scattering theory.…”

“…The nsOCT gives the information content of the FDOCT signal which is based on the general scattering theory. In our previous publication [ 39 – 44 , 46 ], we showed that the FDOCT signal in the axial component of the 3D Fourier transform of spatial frequencies is limited by illumination bandwidth. We also explained the reason why high spatial frequency information is absent in conventional OCT image.…”

Nanosensitive optical coherence tomography for detecting structural changes in stem cells

“…With respect to the second experiment, nsOCT has been utilised to monitor stem cell differentiation in vitro. This work has been previously published examining the direct comparison of positive (chondrogenic differentiation) and negative (undifferentiated controls) cells [ 39 ]. In the present study, this work has been further elaborated to provide information on additional time points of differentiation and how the structural composition of the samples changes throughout this process.…”