KEYWORDS: Optical coherence tomography, Point spread functions, Speckle, Signal processing, Signal analyzers, In vivo imaging, Artificial intelligence, Refractive index, Microscopy, Mathematical modeling
A new formulation of Optical Coherence Tomography (OCT) is presented. This formulation can represent a meaningful OCT image and speckles as two independent mathematical entities. In addition, by using the same formulation strategy, a new imaging modality to generate a spatially differential image, similar to differential interferometric contrast microscopy is demonstrated.
Differential interference microscopy (DIC) is a method to obtain the refractive index distribution of a sample as contrast. It is suitable for biological cells, however, DIC can only obtain 2D images from thin samples. Therefore, we introduce a new imaging method, volumetric differential contrast (VDC) imaging using optical coherence tomography (OCT). This method enables getting 3D differential contrast of thick samples. VDC was designed based on the disperse scatterer model (DSM), a new theoretical model of OCT, and obtains differential contrast by complex numerical processing of OCT signal. DSM represents the sample as a spatially distributed refractive index with dispersed random scatterers, and OCT signal was formulated from this model. VDC uses two complex OCT signals, s1 and s2 at two laterally slightly distant positions, and the final image is defined as Im[s1 s2. This signal forms a spatially differential image of the product of the refractive index distribution and the scatterer density. According to the formulation, the size of the differentiation kernel, corresponding to the shear amount of DIC, is proportional to the defocus of the probe beam and the separation between s1 and s2. This method was validated by an in vitro spheroid sample and an in vivo zebrafish sample, measured by spectral domain OCT with a center wavelength of 830 nm. VDC images were obtained from refocused and defocused signals.
We introduce volumetric differential contrast (VDC) imaging using optical coherence tomography (OCT). This method was designed based on a new theoretical model of OCT, the disperse scatterer model (DSM). VDC gives the differential image of “the product of the refractive index distribution and the scatterer density” through complex numerical processing of OCT signals.
The method was validated by in-vitro and in-vivo samples measured by spectral domain OCT. Differential contrast images with arbitrary shear amount and shear direction were obtained at arbitrary depth positions by a single measurement by numerically applying defocus by holographic signal processing after the signal acquisition.
KEYWORDS: Optical coherence tomography, In vitro testing, 3D modeling, Visualization, Tissues, Stereoscopy, Medical research, Lung, Drug development, Cancer
We demonstrate high-resolution (3.8-µm axial and 4.8-µm lateral) three-dimensional dynamic (D-) OCT imaging by 840-nm spectral domain OCT, and compare it with a low-resolution 1.3-µm D-OCT. The D-OCT images are obtained by logarithmic-intensity-variance method, which is sensitive to the magnitude of signal fluctuation.
Human-induced-pluripotent-stem-cell derived alveolar (lung) organoids and human breast cancer (MCF-7) spheroids were examined. The high-resolution D-OCT revealed the tessellation of high and low dynamics at the matured alveolar epithelium. It is also found that such matured alveolar epithelium exhibits ragged inner surface. For the spheroids, high-scattering spots with low dynamics were observed only in the high-resolution image.
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