This paper presents an adaptation of the widely accepted Monte Carlo method for Multi-layered media
(MCML). Its original Henyey-Greenstein phase function is an interesting approach for describing how light scattering
inside biological tissues occurs. It has the important advantage of generating deflection angles in an efficient - and
therefore computationally fast- manner. However, in order to allow the fast generation of the phase function, the MCML
code generates a distribution for the cosine of the deflection angle instead of generating a distribution for the deflection
angle, causing a bias in the phase function. Moreover, other, more elaborate phase functions are not available in the
MCML code.
To overcome these limitations of MCML, it was adapted to allow the use of any discretized phase function. An
additional tool allows generating a numerical approximation for the phase function for every layer. This could either be a
discretized version of (1) the Henyey-Greenstein phase function, (2) a modified Henyey-Greenstein phase function or (3)
a phase function generated from the Mie theory. These discretized phase functions are then stored in a look-up table,
which can be used by the adapted Monte Carlo code.
The Monte Carlo code with flexible phase function choice (fpf-MC) was compared and validated with the original
MCML code. The novelty of the developed program is the generation of a user-friendly algorithm, which allows several
types of phase functions to be generated and applied into a Monte Carlo method, without compromising the
computational performance.
Food quality is critically determined by its microstructure and composition. These properties could be quantified noninvasively
by means of optical properties (absorption and reduced scattering coefficients) of the food samples. In this
research, a spatially-resolved spectroscopy setup based on a fiber-optic probe was developed for acquiring spatiallyresolved
diffuse reflectance of three sugar foams with different designed microstructures in the range 500 - 1000 nm. A
model for light propagation in turbid media based on diffusion approximation for solving the radiative transport equation
was employed to derive optical properties (absorption and reduced scattering coefficients) of these foams. The accuracy
of this light propagation model was validated on four liquid phantoms with known optical properties. The obtained
results indicated that the optical properties estimation was successfully validated on these liquid phantoms. The
estimated reduced scattering coefficients μs' of the foams clearly showed the effect of foaming time on their
microstructures. The acquired absorption coefficients μa were also in good agreement with the designed ingredients of
these sugar foams. The research results clearly support the potential of spatially-resolved spectroscopy for nondestructive
food quality inspection and process monitoring in the food industry.
In this study, a tool was developed to calculate the bulk optical properties for systems consisting of an absorbing medium
and polydisperse spherical particles that can scatter and/or absorb. The developed tool is based on the Mie-theory for
monodisperse-spherical absorbing and scattering particles in vacuum. First, the original Mie-theory was expanded to also
include physical (real part of refractive index) and chemical (aborption, imaginary part of refractive index) information
of the host medium. Secondly, the polydispersity of the spherical particles was taken into account. Since particle size
distributions (PSD) are typically continuous distributions and Mie-scattering properties can only be calculated for a
monodisperse system, the PSD is fractionated and Mie-scattering properties were calculated for each fraction. These
Mie-scattering properties are then combined with the weight for each fraction to derive bulk optical properties. As the
number of fractions is unknown and needs to be optimized for each calculation, the developed tool keeps on
fractionating until the desired properties (μabs, μsca and P11(cos(θ))) converge to stable values. This flexible tool
allows for the simulation of the bulk optical properties for a wide range of wavelengths, particle volume fractions,
complex refractive indices of both the particles and the medium and PSD's based on normal, lognormal, gamma,
bimodal and custom defined functions. This code was successfully validated for the case of a lognormal PSD of
scattering spheres in vacuum by comparing the simulated values to those reported in literature. The main novelties
of the developed program are the extension of Mie-theory simulations to the case of polydisperse scattering particles in
absorbing media and the automatic optimization of the number of PSD fractions needed to converge.
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