Biomedical subjects

Alwin Kienle

Publications and source records attributed to Alwin Kienle.

4 recordsLinked to original sources

PubMed2006

Light guiding in biological tissue due to scattering.

For a description of light propagation in biological tissue it is usually assumed that tissue is a random medium. We report a pronounced light guiding effect in cubes of human dentin that cannot be described by this standard model. Monte Carlo simulations which consider the microstructure of dentin are performed and successfully compared to experiments. Contrary to explanations so far, we show that light guiding is due to scattering by the tissue's microstructure. Exploiting this concept, light can be guided in arbitrary directions or locations without involving reflections or wave effects.

Dentin↗

PubMed2005

Light diffusion through a turbid parallelepiped.

Solutions of the diffusion approximation to the radiative transport equation are derived for a turbid (rectangular) parallelepiped using the method of image sources and applying extrapolated boundary conditions. The derived solutions are compared with Monte Carlo simulations in the steady-state and time domains. It is found that the diffusion theory is in good agreement with Monte Carlo simulations provided that the light is detected sufficiently far from the incident beam. Applications of the derived solutions, including the determination of the optical properties of the turbid parallelepiped, are discussed.

Animals↗

PubMed2003

Light propagation in dentin: influence of microstructure on anisotropy.

We investigated the dependence of light propagation in human dentin on its microstructure. The main scatterers in dentin are the tubules, the shape of which can be approximated as long cylinders. We calculated the scattering of electromagnetic waves by an infinitely long cylinder and applied the results in a Monte Carlo code that simulates the light propagation in a dentin slab considering multi-scattering. The theory was compared with goniometric measurements. A pronounced anisotropic scattering pattern was found experimentally and theoretically. In addition, intensity peaks were measured which are shown to be caused by light diffraction by the tubules.

Anisotropy↗

PubMedDate not supplied

Phase function measurements on nonspherical scatterers using a two-axis goniometer.

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.

Algorithms↗