Scattering properties of Intralipid modeled using dependent scattering theory

Intralipid^® is widely used as a liquid optical phantom in biomedical optics, but its scattering properties remain incompletely defined, particularly at high volume fractions where dependent scattering becomes important. A physics-based description of its scattering behavior is needed to support quantitative Monte Carlo simulations, phantom design, and calibration of biophotonic measurement systems.

We aim to establish a physically grounded model of Intralipid scattering, including the scattering coefficient, reduced scattering coefficient, anisotropy, and phase function. The model covers wavelengths 400 to 1700 nm and particle volume fractions of 0.00227 to 0.227, corresponding to dilutions from 1% v/v of stock Intralipid 20% through undiluted stock Intralipid 20%. It is derived from intrinsic material properties, namely, the particle size distribution and the refractive indices of the lipid particles and aqueous medium.

We combine full Mie theory for the single-particle scattering response with the multicomponent Percus-Yevick hard-sphere approximation to account for dependent scattering. The model uses recent measurements of the particle size distribution and the refractive-index dispersion of the lipid and aqueous phases. Particular attention is given to the long tail of the particle size distribution, which extends beyond the cutoff of earlier electron-microscopy-based datasets.

Despite its small number fraction, the long tail of the particle size distribution contributes substantially to the scattering coefficient, anisotropy, and phase function, especially at near-infrared wavelengths. The resulting predictions for the scattering coefficient, anisotropy, and reduced scattering coefficient are broadly consistent with established semi-empirical relations for Intralipid in the dependent-scattering regime, although residual wavelength- and concentration-dependent discrepancies remain. The model also provides phase functions across the full studied wavelength and concentration range, for which direct experimental reference data are currently unavailable.

The proposed model links the optical scattering properties of Intralipid to measured material properties while incorporating dependent-scattering effects. Its broad agreement with literature-reported data on IL optical properties supports its use as a physics-based estimate, while the remaining discrepancies highlight the influence of sample variability and the limits of the underlying assumptions. The reported equations and interpolation scripts provide a practical resource for studies requiring internally consistent scattering properties across wavelength and concentration.