Estimation of biological chromophores using diffuse optical spectroscopy: benefit of extending the UV-VIS wavelength range to include 1000 to 1600 nm

Abstract

With an optical fiber probe, we acquired spectra from swine tissue between 500 and 1600 nm by combining a silicon and an InGaAs spectrometer. The concentrations of the biological chromophores were estimated by fitting a mathematical model derived from diffusion theory. The advantage of our technique relative to those presented in previous studies is that we extended the commonly-used wavelength ranges of 500 and 1000 nm to include the range of 1000 to 1600 nm, where additional water and lipid absorption features exist. Hence, a more accurate estimation of these two chromophores is expected when spectra are fitted between 500 and 1600 nm than between 500 and 1000 nm. When extending the UV-VIS wavelength range, the estimated total amount of chromophores approached 100% of the total as present in the probed volume. The confidence levels of the water and lipid related parameters increases by a factor of four.

Fig. 1

Sketch of the optical setup: it consists of a halogen lamp that is connected to a fiber and two spectrometers that are connected to two separate fibers that are located next to each other at the tip of the probe.

Fig. 2

Absorption coefficient of deoxygenated hemoglobin (full line), oxygenated hemoglobin (dashed line), water (dotted line) and lipid (dashed-dotted line) from 500 to 1600 nm.

Fig. 3

Typical measurement of muscle and fat layer (dotted line), and the corresponding fits and residuals between 500 and 1600 nm (full line).

Fig. 4

Estimated water and lipid volume fraction (dots) when fitting between 500 and 1000 nm versus 500 and 1000 nm and the respective mean and standard deviation.

Fig. 5

Comparison of confidence intervals obtained when fit is applied between 500 and 1000 nm and 500 and 1600 nm of the blood volume fraction (stars), blood saturation (circles), water and lipid volume fraction (crosses) and lipid fraction in the total volume (squares).

Fig. 6

Comparison of the estimated reduced scattering amplitude when fit is applied between 500 and 1000 nm (Fit 1) and 500 and 1600 nm (Fit 2) where the circles correspond to no statistical difference in absolute values and the crosses with statistical differences (a). The corresponding water and lipid volume fractions shows larger deviation from 100% when Fit 1 is applied (b). The corresponding blood volume fraction shows overestimations of the values when Fit 1 is applied (c).