Liquid phantoms for near-infrared and diffuse correlation spectroscopies with tunable optical and dynamic properties

Abstract

We present the recipe and characterization for preparing liquid phantoms that are suitable for both near-infrared spectroscopy and diffuse correlation spectroscopy. The phantoms have well-defined and tunable optical and dynamic properties, and consist of a solution of water and glycerol with fat emulsion as the scattering element. The recipe takes into account the effect of bulk refractive index changes due to the addition of glycerol, which is commonly used to alter the sample viscosity.

Keywords: (170.3660) Light propagation in tissues; (170.6480) Spectroscopy, speckle; (290.0290) Scattering; (290.1990) Diffusion.

Fig. 1

In panel (a) the reduced scattering coefficient (${\mu }_s^{\mathrm{\prime }}$) at λ = 785 nm as a function of scatterer concentration at different glycerol concentrations is shown. The dots represent the reduced scattering coefficient measured and the lines the corresponding linear fit. In this case, we have excluded data from the lowest concentrations of scatterers since at such low values of reduced scattering coefficient the diffusion theory is not valid. In panel (b), the intrinsic reduced scattering coefficient of Lipofundin (∊_s) for varying glycerol concentrations is shown for three wavelengths. Lines represent the linear fits performed. In panel (c), the intrinsic reduced scattering coefficient of Lipofundin (∊_s) for varying wavelengths and different glycerol concentrations is shown. Lines represent the fits performed using the empirical Mie relation (equation 4). Finally, in panel (d), the absorption coefficient (μ_a) spectrum at a fixed scatterer concentration is shown over wavelength. Different colored dots correspond to different glycerol concentrations. The measurements are overlapped with the water absorption spectrum (line). Please note that the concentrations reported in the x-axes of panels (a) and (b) are expressed in % (normalized to 100), while, when reporting the results of the fits in Section 3.3, the concentrations are reported for consistence with literature in g/g (normalized to 1).

Fig. 2

Results of the two independent DCS experiments (ICFO 1 and ICFO 2) for different glycerol and scatterer concentrations. Detailed results are reported in Table 4, Section 3.3.