Verification of a two-layer inverse Monte Carlo absorption model using multiple source-detector separation diffuse reflectance spectroscopy

Abstract

A two-layer Monte Carlo lookup table-based inverse model is validated with two-layered phantoms across physiologically relevant optical property ranges. Reflectance data for source-detector separations of 370 μm and 740 μm were collected from these two-layered phantoms and top layer thickness, reduced scattering coefficient and the top and bottom layer absorption coefficients were extracted using the inverse model and compared to the known values. The results of the phantom verification show that this method is able to accurately extract top layer thickness and scattering when the top layer thickness ranges from 0 to 550 μm. In this range, top layer thicknesses were measured with an average error of 10% and the reduced scattering coefficient was measured with an average error of 15%. The accuracy of top and bottom layer absorption coefficient measurements was found to be highly dependent on top layer thickness, which agrees with physical expectation; however, within appropriate thickness ranges, the error for absorption properties varies from 12-25%.

Effect of probe geometry and optical properties on the sampling depth for diffuse reflectance spectroscopy

“…[1][2][3][4][5][6][7][8][9][10][11] Typically, DRS uses a fiber to inject light into the tissue. The light undergoes scattering and absorption, and the reflected light is collected by a second fiber placed at a short distance, known as the sourcedetector separation (SDS), from the illumination fiber.…”

“…The collected light contains quantitative information which can be extracted using an inverse model that relates the collected signal to tissue optical properties. 1,2 Since the reflected light only contains information about the tissue that it passes through, accurate interpretation of the results requires knowledge of the penetration depth. The light penetration depth depends not only on the absorption and scattering properties of the tissue, but also on the geometry of the diffuse reflectance probe.…”

Impact of one-layer assumption on diffuse reflectance spectroscopy of skin

“…16 A fourdimensional MCLUT was created using a two-dimensional MC code written in ANSI C 22 implemented on an NVIDIA GTX 560 Ti GPU on 386 parallel threads. 23 The refractive index above the tissue was set to 1.45 to match the refractive index of an optical fiber, and the refractive index of the medium was set to 1.4 to match the refractive index of tissue.…”

“…Spectra are generated by first selecting the following properties: (1) epidermal thickness (Z 0 ), (2) Reduced scattering at all wavelengths is calculated using Eq. (1), which is commonly used in tissue optics, [13][14][15][16] …”

“…Some multilayered inverse models of skin have been developed to overcome this problem. [16][17][18][19][20][21] While depth-dependent heterogeneities were analyzed in this study, heterogeneities that are spatially in the plane of detection were not considered. Such heterogeneities would include the border of a nevus or other concentrations of pigment in the skin as well as the localization of hemoglobin in vessels which was investigated by Fredriksson et al 20 Additionally, Fredriksson et al generated a spectra using a two-layer model of skin with individual blood vessels and fit those spectra with a one-layer model.…”