Abstract
Quantification of tissue optical properties with optical coherence tomography (OCT) has proven to be useful in evaluating structural characteristics and pathological changes. Previous studies primarily used an exponential model to analyze low numerical aperture (NA) OCT measurements and obtain the total attenuation coefficient for biological tissue. In this study, we develop a systematic method that includes the confocal parameter for modeling the depth profiles of high NA OCT, when the confocal parameter cannot be ignored. This approach enables us to quantify tissue optical properties with higher lateral resolution. The model parameter predictions for the scattering coefficients were tested with calibrated microsphere phantoms. The application of the model to human brain tissue demonstrates that the scattering and back-scattering coefficients each provide unique information, allowing us to differentially identify laminar structures in primary visual cortex and distinguish various nuclei in the midbrain. The combination of the two optical properties greatly enhances the power of OCT to distinguish intricate structures in the human brain beyond what is achievable with measured OCT intensity information alone, and therefore has the potential to enable objective evaluation of normal brain structure as well as pathological conditions in brain diseases. These results represent a promising step for enabling the quantification of tissue optical properties from high NA OCT.
Highlights
Optical coherence tomography (OCT) has been widely used to investigate tissue microstructure in both clinical and scientific studies due to its high resolution and 3D imaging capability
We have shown that OCT with 3.5μm lateral resolution is able to differentiate laminar structures in the neocortex of human brain samples by using the average intensity projection (AIP) over the effective depth range [17]
The variations of the OCT intensity in the white matter have been shown both in ex vivo rodent and human brain imaging [8], [17], and the extraction of μ' in the current study provides a further explanation for the observations
Summary
Optical coherence tomography (OCT) has been widely used to investigate tissue microstructure in both clinical and scientific studies due to its high resolution and 3D imaging capability. The depth profiles (A-lines) created with OCT are generally prescribed by four factors: the sample refractive index, attenuation coefficient, backscattering coefficient, and the numerical aperture (NA) of the focusing optics. The attenuation coefficient has been routinely extracted from OCT measurements based on Beer’s law, which is appropriate for low NA measurements. This simple model has proven to be useful in detecting cancerous tissues in skin, bladder and brain [1,2,3], monitoring blood glucose concentration [4], characterizing atherosclerosis plaques [5,6] and correlating collagen content with histological staining [7]. It has been reported that for the majority of biological tissues, the contribution of multiple scattering in the OCT image is fairly small, usually less than 10% [14]
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