Study of optical properties and proteoglycan content of tendons by polarization sensitive optical coherence tomography

Abstract

The highly orientated collagen fibers in tendons play a critical role for transferring tensile stress, and they demonstrate birefringent optical properties. However, the influence that proteoglycans (PGs) have on the optical properties of tendons is yet to be fully elucidated. PGs are the essential components of the tendon extracellular matrix; the changes in their quantities and compositions have been associated with tendinopathies. In this study, polarization sensitive optical coherence tomography (PS-OCT) has been used to reveal the relationship between PG content/location and birefringence properties of tendons. Fresh chicken tendons were imaged at regular intervals by PS-OCT and polarization light microscopy during the extraction of PGs, using guanidine hydrochloride (GuHCl). Complementary time-lapsed images taken from the two modalities mutually demonstrated that the extraction of PGs disturbed the local organization of collagen bundles. This corresponded with a decrease in birefringence and associated banding pattern observed by PS-OCT. Furthermore, this study revealed there was a higher concentration of PGs in the outer sheath region than in the fascicles, and therefore the change in birefringence was reduced when extraction was performed on unsheathed tendons. The results provide new insights of tendon structure and the role of PGs on the structural stability of tendons, which also demonstrates the great potential for using PS-OCT as a diagnostic tool to examine tendon pathology.

Spectral binning for mitigation of polarization mode dispersion artifacts in catheter-based optical frequency domain imaging

“…This capability is particularly useful in biological tissue with regularly arranged fibrous architecture, such as collagen, that may induce form-birefringence and result in a measurable retardation signal. PS-OCT has been used to image collagen-rich tissues such as tendon and cartilage [4,5], the loss of birefringence signal in skin burns [6], and in ophthalmology, where it enables a more detailed interpretation of the retinal structures such as the birefringent retinal nerve fiber layer [7][8][9][10]. The birefringence signal measured with PS-OFDI has also been shown to correlate with collagen content of aortic plaques, which could serve as a predictor of plaque vulnerability [11,12].…”

Advanced glycation products’ levels and mechanical properties of vaginal tissue in pregnancy

“…Certain proteoglycans also modulate fibrillogenesis and fiber alignment (30). Studies have shown that removal of GAGs results in disorganization of collagen fibrils (31). GAGs present between collagen fibrils in connective tissues may aid their arrangement, resisting complete fiber disorganisation during stretching.…”

Polarization Sensitive Optical Coherence Tomography: A Review of Technology and Applications

“…Consequently, PS-OCT was used to visualize the evolution of the collagen fiber alignment via birefringence in tissue-engineered tendons in response to varying growth environments and to investigate degenerative changes related to rupture in Achilles tendons [190,191]. Lately, the influence of proteoglycans-which are essential components of the tendon extracellular matrix associated with tendinopathies-on the optical properties of tendons have been studied by PS-OCT [192]. In skeletal muscle of genetically-altered (mdx) mice, exercise-induced ultrastructural changes were detected by PS-OCT in in vivo animals [193].…”