Abstract
.Significance: The spatial organization of collagen fibers has been used as a biomarker for assessing injury and disease progression. However, quantifying this organization for complex structures is challenging.Aim: To quantify and classify complex collagen fiber organizations.Approach: Using quantitative second-harmonic generation (SHG) microscopy, we show that collagen-fiber orientation can be viewed as pseudovector fields. Subsequently, we analyze them using fluid mechanic metrics, such as energy , enstrophy , and tortuosity .Results: We show that metrics used in fluid mechanics for analyzing fluid flow can be adapted to analyze complex collagen fiber organization. As examples, we consider SHG images of collagenous tissue for straight, wavy, and circular fiber structures.Conclusions: The results of this study show the utility of the chosen metrics to distinguish diverse and complex collagen organizations. We find that the distribution of values for and increases with collagen fiber disorganization, where they divide between low and high values corresponding to uniformly aligned fibers and disorganized collagen fibers, respectively. We also confirm that the values of cluster around 1 when the fibers are straight, and the range increases up to 1.5 when wavier fibers are present.
Highlights
Collagen is the primary structural protein in the extracellular matrix and in connective tissue.[1,2] The organization of collagenous fibers could be used as a biomarker for structural anomalies, disease diagnosis and progression, aging, tissue development, and damage.[1,3,4,5,6,7] The noncentrosymmetric molecular assembly of fibrillar collagen produces a nonlinear optical response when it interacts with light where two input photons produce an output photon with twice the frequency, a process known as second-harmonic generation (SHG).[8]
We find that the distribution of values for E and U increases with collagen fiber disorganization, where they divide between low and high values corresponding to uniformly aligned fibers and disorganized collagen fibers, respectively
An analytical approach based on fluid mechanics enables assessment of fiber orientation as part of a unified system of vectors akin to fluid flow
Summary
Collagen is the primary structural protein in the extracellular matrix and in connective tissue.[1,2] The organization of collagenous fibers could be used as a biomarker for structural anomalies, disease diagnosis and progression, aging, tissue development, and damage.[1,3,4,5,6,7] The noncentrosymmetric molecular assembly of fibrillar collagen produces a nonlinear optical response when it interacts with light where two input photons produce an output photon with twice the frequency, a process known as second-harmonic generation (SHG).[8]. Various types of quantitative SHG imaging methods have been used to contribute to understanding the role of collagen microstructure in biological function.[4,6,9,10,11] For example, the texture analysis methods have been used to quantitatively classify SHG images for normal and Journal of Biomedical Optics
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