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Abstract
Quantification of chromophore concentrations in reflectance mode remains a major challenge for biomedical optics. Spectroscopic Optical Coherence Tomography (SOCT) provides depth-resolved spectroscopic information necessary for quantitative analysis of chromophores, like hemoglobin, but conventional SOCT analysis methods are applicable only to well-defined specular reflections, which may be absent in highly scattering biological tissue. Here, by fitting of the dynamic scattering signal spectrum in the OCT angiogram using a forward model of light propagation, we quantitatively determine hemoglobin concentrations directly. Importantly, this methodology enables mapping of both oxygen saturation and total hemoglobin concentration, or alternatively, oxyhemoglobin and deoxyhemoglobin concentration, simultaneously. Quantification was verified by ex vivo blood measurements at various pO2 and hematocrit levels. Imaging results from the rodent brain and retina are presented. Confounds including noise and scattering, as well as potential clinical applications, are discussed.
Highlights
While many biomedical optical diagnostic and imaging techniques must be performed in reflectance mode, quantitative measurements of tissue chromophore concentrations using reflected light remain challenging
Spectroscopic Optical Coherence Tomography (OCT) (SOCT) [4,5,6,7,8,9,10,11,12,13,14] can determine depth-resolved spectra, from which quantification of chromophores based on spectroscopic analysis can be achieved if the path length is known [15]
We extend a previous description of the complex OCT signal [32] to include spectroscopic (λ or k = 2π/λ) dependence
Summary
While many biomedical optical diagnostic and imaging techniques must be performed in reflectance mode, quantitative measurements of tissue chromophore concentrations using reflected light remain challenging. Methods such as photoacoustic microscopy (PAM) [1] and photothermal Optical Coherence Tomography (OCT) [2,3] quantify absorption in an excited volume, which can be related to chromophore concentration if multiple excitation wavelengths are used. Tissue and blood scattering are much higher than absorption at near-infrared wavelengths. As red blood cell scattering depends on wavelength, orientation, and oxygen saturation [17,18], quantification may be compromised. Recent work using visible wavelength OCT has shown the feasibility of achieving saturation measurements using both parametric [12,20,21] and non-parametric approaches [13,22]
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