The optic axis of birefringent tissues indicates the direction of structural anisotropy. Polarization-sensitive Optical Coherence Tomography (PS-OCT) can provide reflectivity contrast as well as retardance and optic axis orientation contrasts that originate from tissue birefringence. We introduce imaging 3D tissue anisotropy by using a single-camera and polarization-maintaining fiber (PMF) based PS-OCT, which utilizes normal and angled illuminations.
Because environmental factors such as the movement of PMF and temperature fluctuations induce arbitrary phase changes, the optic axis orientation measurement has a time-varying offset. In order to measure the absolute axis orientation, we add a calibration path which dynamically provides the arbitrary offset to be subtracted from the relative axis orientation values.
The axis orientation on the normal plane is the 2D projection of the fiber direction in 3D space. We propose to characterize the axis orientation in different planes (xy, xy’ and x’y planes) by using normal and angled illuminations. This allows calculation of the polar angle that completes the orientation information in 3D. Polarization-based optical systems relying on one illumination angle measure the “apparent birefringence” that light encounters rather than the “true birefringence”. Birefringence as a measure of anisotropy is quantified with the orientation information in 3D. The method and validation with a biological tissue are presented. The study can facilitate imaging and mapping the structural connections in anisotropic tissues including the brain.
Chao Liu, Adam J. Black, Hui Wang, and Taner Akkin, "Quantifying axis orientation in 3D using polarization-sensitive optical coherence tomography
(Conference Presentation)," Proc. SPIE 9690, Clinical and Translational Neurophotonics; Neural Imaging and Sensing; and Optogenetics and Optical Manipulation, 96901E (Presented at SPIE BiOS: February 16, 2016; Published: 26 April 2016); https://doi.org/10.1117/12.2217637.4848636568001.
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