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Modeling optical behavior of birefringent biological tissues for evaluation of quantitative polarized light microscopy

“…Also, the linear relationship between collagen density and measured retardance is implicitly assumed when observed retardances are scaled with sample thickness 39,40,46,60 and experimentally observed in the linear relationship between retardance and sample thickness. 27,42 Our experiments with tendon confirm this: both retardance and azimuth of combinations of different amounts of birefringent material forming different simple networks can be predicted by the model using linear optical behavior for collagen.…”

“…A collagen network that is not invariant to the plane of cutting will give different results depending on the orientation of the cutting plane. This was experimentally shown by Király et al 42 Superficial split line patterns indicate the predominant orientation of collagen fibers in the most superficial cartilage layer across the articular surface. Király et al found that sections cut perpendicular to these split lines showed decreased retardance in the superficial zone compared to sections cut parallel to the superficial split lines.…”

“…When the thickness of a histological section is increased, measured retardance will increase linearly with thickness only when it is safe to assume that collagen architecture and density are uniform over the thickness of the section. 27,42,61 Within a sample, relevant differences in collagen density can exist. In our example, adopted from the literature, 57 the minimum collagen density is approximately 60% of the maximum.…”

“…We will use retardance to indicate measured extrinsic optical retardations. 32,39,40 This property is sometimes also called optical path difference, [41][42][43] birefringence intensity, 17,44 or rotation independent birefringence. 45 From retardances measured with different states of polarized light, we can calculate the azimuth.…”

Translational and Rotational Dynamics of Water Molecules in Aligned Collagenous Tissues: Implications for Assessing Collagen Organisation with Magnetic Resonance Imaging

“…SEM allows high resolution micrographs commonly used to measure fibre and fibril diameters and assess collagen alignment on micrometre to nanometre scales by examination of individual fibrils [8,[21][22][23]25,28]. The collagen ultrastructure can also be quantified using PLM [27,90,101,102], which constructs 2D images of the fibril orientation (angle), organisation/anisotropy (retardance) by measuring the optical birefringence of a group of fibrils within an imaging pixel (~ 1 μm). Other non-linear optical microscopy techniques [103] and X-ray scattering [104][105][106] also probe collagen fibre alignment.…”