Tissue optical properties can be determined with optical coherence tomography (OCT) by fitting a model to the OCT signal. Using calibrated samples in the fixed focus geometry, the validity of the single-scattering and multiple-scattering models for both highly scattering and weakly scattering media (scattering coefficients mu(s) ranging from 1.25 to 25.11mm(-1)) has been investigated. The results show that, with a proper correction for the confocal properties of the sample arm, both models are appropriate to extract the scattering coefficients of weakly scattering media. For highly scattering media, the multiple scattering should be taken into account, and the multiple-scattering model can provide higher accuracy. Finally, the scattering properties of in vitro rat liver and in vivo human skin are determined. The results are useful for quantitatively characterizing tissue scattering in biomedical research and clinical diagnosis.
The effect of the two-point spatial correlation function of human tissue on the spectrum of scattered light is considered within the accuracy of the first Born approximation. An expression for the maximum of the spectrum of the scattered light at various scattering angles is derived. It is shown that for most biological tissues the spectrum of the backscattered light is centered at a higher frequency with respect to the incident spectrum.
We report rapid and high-resolution tomographic en face imaging of human liver specimens by full-field optical coherence tomography (FF-OCT). First, the arrangement of the FF-OCT system was described and the performance of the system was measured. The measured axial and lateral resolutions of the system are 0.8 and 0.9 μm, respectively. The system has a sensitivity of ∼60 dB and can achieve an imaging rate of 7 fps and a penetration depth of ∼80 μm. The histological structures of normal liver can be seen clearly in the en face tomographic images, including central veins, cords of hepatocytes separated by sinusoidal spaces, and portal area (portal vein, the hepatic arteriole, and the bile duct). A wide variety of histological subtypes of hepatocellular carcinoma was observed in en face tomographic images, revealing notable cancerous features, including the nuclear atypia (enlarged convoluted nuclei), the polygonal tumor cells with obvious resemblance to hepatocytes with enlarged nuclei. In addition, thicker fibrous bands, which make the cytoplasmic plump vesicular nuclei indistinct, were also seen in the images. Finally, comparison between the portal vein in a normal specimen versus that seen in the rare type of cholangiocarcinoma was made. The results show that the cholangiocarcinoma presents with a blurred pattern of portal vein in the lateral direction and an aggregated distribution in the axial direction; the surrounding sinusoidal spaces and nuclei of cholangiocarcinoma are absent. The findings in this work may be used as additional signs of liver cancer or cholangiocarcinoma, demonstrating capacity of FFOCT device for early cancer diagnosis and many other tumor-related studies in biopsy.
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