Measuring tissue optical properties in vivo using reflectance-mode confocal microscopy and OCT

Steven L. Jacques; Ravikant Samatham; Niloy Choudhury; Yongji Fu; David Levitz

doi:10.1117/12.761803

1 March 2008 Measuring tissue optical properties in vivo using reflectance-mode confocal microscopy and OCT

Steven L. Jacques, Ravikant Samatham, Niloy Choudhury, Yongji Fu, David Levitz

Proceedings Volume 6864, Biomedical Applications of Light Scattering II; 68640B (2008) https://doi.org/10.1117/12.761803
Event: SPIE BiOS, 2008, San Jose, California, United States

Abstract

The ability to separately measure the scattering coefficient (μ_s [cm^-1]) and the anisotropy (g) is difficult, especially when measuring an in vivo site that can not be excised for bench-top measurements. The scattering properties (μ_s and g) can characterize the ultrastructure of a biological tissue (nuclear size, mitochondra, cytoskeletion, collagen fibers, density of membranes) without needing an added contrast agent. This report describes the use of reflectance-mode confocal scanning laser microscopy (rCSLM) to measure optical properties. rCSLM is the same as optical coherence tomography (OCT) when the OCT is conducted in focus-tracking mode. The experimental measurement involves translating the depth of focus, z_f, of an objective lens, down into a tissue. As depth z increases, the reflected signal R decreases due to attenuation by the tissue scattering (and absorption, μ_a). The experimental data behaves as a simple exponential, R(z) = ρ exp(-μz_f) where ρ is the local reflectivity (dimensionless) and μ [cm^-1] is an attenuation coefficient. The relationship between (ρ,μ) and (μ_s,g) is: μ = (μ_s a(g) + μ_a) 2 G(g,NA) ρ = μ_s L_f b(g,NA) where a(g) is a factor that drops from 1 to 0 as g increases from 0 to 1 (determined by Monte Carlo simulations) allowing photons to reach the focus despite scattering, G is a geometry factor describing the average photon pathlength that depends on the numerical aperture (NA) of the lens and the anisotropy (g), L_f is the axial extent of the focus, and b(g,NA) is the fraction of scattered light that backscatters into the lens for detection.

Citation Download Citation

Steven L. Jacques, Ravikant Samatham, Niloy Choudhury, Yongji Fu, and David Levitz "Measuring tissue optical properties in vivo using reflectance-mode confocal microscopy and OCT", Proc. SPIE 6864, Biomedical Applications of Light Scattering II, 68640B (1 March 2008); https://doi.org/10.1117/12.761803

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