Abstract
A technique for creating maps of the direction and strength of fiber alignment in collagenous soft tissues is presented. The method uses a division of focal plane polarimeter to measure circularly polarized light transmitted through the tissue. The architecture of the sensor allows measurement of the retardance and fiber alignment at the full frame rate of the sensor without any moving optics. The technique compares favorably to the standard method of using a rotating polarizer. How the new technique enables real-time capture of the full angular spread of fiber alignment and retardance under various cyclic loading conditions is illustrated.
Highlights
Collagen fibers are the primary component providing structural support for most soft tissues, so observation of collagen alignment can provide insight into how tissues will behave under load and can yield clues to the overall health of the tissue.[3,4]
We show that this type of sensor allows real-time capture of collagen alignment dynamics at high spatial resolutions, which will be an extremely useful tool for further studies of tissue biomechanics
A polarizationsensitive imaging sensor will capture the Stokes vector that emerges from this tissue and the goal is to solve for this rotation angle, θ, and for the retardance, φ. Solving for these two parameters, namely θ and φ, requires multiple measurements of the Stokes parameters S1 or S2, which is typically accomplished by rotating an analyzer. If both S1 and S2 are known, this leads to computation of the angle of polarization (AoP), which describes the major axis of rotation of the polarized light
Summary
The study of the biomechanics of tissue is an active area of research.[1,2] Collagen fibers are the primary component providing structural support for most soft tissues, so observation of collagen alignment can provide insight into how tissues will behave under load and can yield clues to the overall health of the tissue.[3,4] Such observations lead to a greater understanding of how tissues function in normal loading regimes and throughout damage/failure, knowledge that can be used to help speed recovery and may even be used to guide the development of engineered replacement tissues. Measuring the microstructural arrangement of tissues during periods of loading and rest will lead to a better understanding of the structure–function relationships of a variety of tissue types across many different organisms. A common method for evaluating collagen fiber alignment in soft tissues observes the change and direction of birefringence under different loading conditions. Our method requires only circularly polarized input light, and we use a 1-Mp division of focal plane polarimeter to make our observations in real-time, i.e., at 30 frames per second. We show that this type of sensor allows real-time capture of collagen alignment dynamics at high spatial resolutions, which will be an extremely useful tool for further studies of tissue biomechanics. Simple, and requires no moving optics, and does not require a static field-of-view during measurement
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