The collagen structure of equine articular cartilage, characterized using polarization-sensitive optical coherence tomography

Abstract

Optical coherence tomography and polarization-sensitive optical coherence tomography images of equine articular cartilage are presented. Measurements were made on intact joint surfaces. Significant (e.g. × 2) variations in the intrinsic birefringence were found over spatial scales of a few millimetres, even on samples taken from young (18 month) animals that appeared visually homogeneous. A comparison of data obtained on a control tissue (equine flexor tendon) further suggests that significant variations in the orientation of the collagen fibres relative to the plane of the joint surface exist. Images of visually damaged cartilage tissue show characteristic features both in terms of the distribution of optical scatterers and of the birefringent components.

A review of some recent developments in polarization-sensitive optical imaging techniques for the study of articular cartilage

“…Our work on equine cartilage however has emphasised that PS-OCT measures what we term the "apparent birefringence" which is determined not only by the biochemical constitution of the tissue but also by the 3-D structural arrangement of the fibres 23 , an observation that has subsequently been confirmed by Xie et al 37 , who went on to compare the 3-D structure of cartilage and meniscus using an approach similar to ours.…”

“…by the author's group in relation to our PS-OCT studies of articular cartilage 23 . The distinction is discussed more fully in the next section, but basically amounts to the observation that, regardless of its underlying origin -intrinsic or form -the birefringence value ∆n that is extracted from a phase-retardation map is dependent not only on the underlying birefringence properties of the sample but also on the geometrical arrangement between the probing light beam and the 3-D spatial orientation of the fiber long-axis of the collagen.…”

Collagen fiber arrangement in normal and diseased cartilage studied by polarization sensitive nonlinear microscopy

“…Polarized light microscopy, small and wide-angle x-ray scattering, and polarization sensitive optical coherence tomography ͑PSOCT͒ have been employed in a number of important and revealing studies. [3][4][5] The latter has the great attraction, because it can provide depth imaging on tissue attached to subchondral bone, thus opening the prospect of imaging in the intact joint. However, the depth and lateral resolution of PSOCT are too low to address many structural issues pertinent to cartilage pathophysiology, and in the present work, we investigate the ability of multiphoton microscopy to fulfill this need.…”

“…We first study tendon as an example of a highly ordered collagenous structure whose birefringence and biattenuance have been characterized in some detail. 3,23 We then analyze normal cartilage and lesions in the equine metacarpophalangeal joint. This tissue was selected because its structure has been extensively characterized by other methods, 3,4 and the lesions that develop spontaneously share many of the characteristics of human disease.…”

A Computational Framework for Patient‐Specific Analysis of Articular Cartilage Incorporating Structural Information from DT‐MRI

“…There is also considerable interest in determining the structural arrangement of collagen fibres non-destructively. Methods to accomplish this include: differential interference contrast light microscopy [21], small angle X-ray scattering (SAXS) [22][23][24], optical coherence tomography and polarisation sensitive optical coherence tomography [25,26], spin-spin relaxation time T2-weighted MRI [27,28] and high-field diffusion tensor magnetic resonance imaging (DT-MRI) [20,[28][29][30].…”