Figure 2.

Simulated 3D-PLI reference dataset. (A) The standard 3D-PLI measurement yields 18 images corresponding to equidistant rotation angles ρ between 0° and 170°. Here, a selection of nine generated images of simulated birefringent structures (the letter R and the ± sign) is shown. Each image has a size of 200 × 200 pixels. The varying pixel intensities are comparable to observed signals in measurements of brain sections. The red squares indicate a native voxel of interest that is displayed (B) in terms of the observed light intensity as a function of the rotation angle. The physical model that underlies 3D-PLI provides a sinusoidal description of the simulation (continuous black line), and relates (C) its amplitude to the inclination angle α via the retardation value sinδand (D) its phase to the direction angle φ. The introduced effects of blurring and noise are evident: the minus sign in the direction map (D), for example, shows direction angles that are spread around the initial direction φ = 0° by±2.5°. In a π-periodic system, this is equivalent to an angle range between 177.5° and 2.5°. (E) Visualization of the FOM with the determined vectors $\vec{\text{u}}$ encoded in RGB color space (see color sphere for the relation between orientation and color-coding).