Theory and Simulation

Two complementary simulation approaches are pursued to better understand the physics behind light-matter interactions in brain tissue and to develop general concepts of how the measurement and signal analysis of 3D Polarized Light Imaging (3D-PLI) can be improved: a linear optics approach (figure, in the middle) and an electrodynamics approach (figure, on the right). For the simulations, highly-dense nerve fiber models are generated (figure, on the left), reflecting the nerve fiber architecture of the brain. The simulations are performed on supercomputers in cooperation with the Jülich Supercomputing Centre (JSC).

Matrix Calculus (Lineare Optik)

The simulation approach based on linear optics models the birefringence of nerve fibers as series of matrices. The simulations reproduce the entire 3D-PLI measurement, starting from synthetic nerve fiber arrangements and ending with measurement-like tissue images (fiber orientation map). A comparison of the known underlying fiber model (figure, in the middle) with the fiber orientations derived in a standard 3D-PLI measurement (figure, on the left) helps to identify possible misinterpretations in the fiber reconstruction process.

Maxwell Solver (Electrodynamics)

The simulation approach based on electrodynamics computes the propagation of light by solving Maxwell’s equations which describe light as electromagnetic wave. In this way, more complex light-matter interactions like scattering and interference of light can be studied, enabling to model e.g. the intensity of light transmitted through a brain sample (see figure): The simulations show that regions (cg) with out-of-plane nerve fibers (α = 70°) scatter the light in almost all directions so that less light is detected by the camera than for regions (cc) with in-plane nerve fibers (α = 0°).