We developed a method to determine the optical properties of biological tissue from the results of integrating
sphere measurements. Our Monte Carlo model developed for this purpose considered the geometry of the
investigated sample as well as the features of the integrating sphere setup. To improve the accuracy of our
results, we incorporated the wavelength dependence of the anisotropy factor of the investigated tissue into the
Monte Carlo model. To determine the anisotropy factor, we performed goniometric measurements on six porcine
dura mater tissue samples and quantified the phase function at a wavelength of 650 nm. The averaged anisotropy
factor was taken into account in the Monte Carlo simulations. The result of these simulations were combined
in a table lookup. We used this table lookup to interpret the results from the integrating sphere measurements.
We present as a result of our measurements the absorption coefficient and the reduced scattering coefficient of
porcine dura mater tissue in the wavelength range of 450 to 650 nm.
With the help of a solution of the transport equation it is possible to calculate the light propagation in biological tissue
quite precisely if the exact phase function of the scattering tissue is known. The phase function of most structured tissues
depends on two scattering angles (polar and azimuthal angle) and the direction of the incident light. Even though the use
of the complete phase function is crucial for a precise calculation of the light propagation and the only way to understand
e.g. the anisotropic light propagation in structured tissue, typically phase functions are used which depend only on one
scattering angle. This simplification is most likely due to missing measurement data of more realistic phase functions of
biological tissues. In this article we present goniometric measurements of the phase function of porcine skeletal muscle
for the whole solid angle and different incident directions.
Diameters of single polystyrene beads were determined within ~10 nm accuracy by comparing Mie theory oscillations
and wavelength resolved measurements. The setup is realized with an axicon supported reflected darkfield microscope
and is herein presented in detail. Further we explain a theoretical model considering the effective numerical aperature of
the measuring system. A fitting algorithm allows rapid characterization of the sphere diameters.
We studied the angular distribution of remitted and reflected light from rough turbid biological media. The
remission and reflection are studied separately, then they are compared with each other. The angular distribution
of the reflection/remission from 'reflecting standards' is investigated.
Fat emulsions like Intralipid are frequently used in research of light propagation in turbid media as tissue phantoms. We investigated the optical properties, the scattering coefficient &mgr;s, the reduced scattering coefficient &mgr;s' and the anisotropy factor g of different major brands and different fat concentrations (10% and 20%) of these fat emulsions in the visible from 450nm to 950nm. The phase function was measured with a goniometrical setup and the anisotropy factor was calculated from this. A collimated transmission setup was used to measure &mgr;s. Significant differences were found between the different brands and between different concentrations of the same brand. We also found significant differences compared to the values published in literature.
We present a two-axis goniometer for measuring the phase function of scattering media with an angular resolution of about 0.2 deg having 12 decades of dynamic range and covering almost the full solid angle. The setup is evaluated with polystyrene spheres and with perpendicularly and obliquely illuminated thin glass cylinders. The scattering pattern and its intensity distribution are in excellent agreement with analytical theory. A multiple scattering configuration composed of two parallel cylinders is also examined. Finally, the phase function of dentin slabs is measured and its dependence on the dental microstructure is discussed.
Fat emulsions like Intralipid are frequently used in research of light propagation in turbid media as tissue phantoms. We investigated the phase functions of different major brands and concentrations (10% and 20%) of these fat emulsions at 633nm and 543nm. A theoretical phase function for fat emulsions was calculated using Mie theory. Only small differences of the phase function of the investigated fat emulsions were found.
The light propagation in biological tissue having anisotropic optical properties is investigated. Monte Carlo
simulations employing the phase function of infinitely long cylindrical scatterers and the Henyey-Greenstein function are performed and compared to spatially-resolved reflectance measurements of semi-infinite turbid media. In addition, simulations are shown for the spatially-resolved reflectance and transmittance from the surfaces of cubic turbid media. It is found that the light propagation in anisotropic turbid media is very different compared to turbid media that have isotropic optical properties.
For example, it is observed that the light which is incident perpendicular to the top surface of the cube may be
transmitted mainly from a single lateral side.