Effects of optical beam angle on quantitative optical coherence tomography (OCT) in normal and surface degenerated bovine articular cartilage

Abstract

Quantitative measurement of articular cartilage using optical coherence tomography (OCT) is a potential approach for diagnosing the early degeneration of cartilage and assessing the quality of its repair. However, a non-perpendicular angle of the incident optical beam with respect to the tissue surface may cause uncertainty to the quantitative analysis, and therefore, significantly affect the reliability of measurement. This non-perpendicularity was systematically investigated in the current study using bovine articular cartilage with and without mechanical degradation.Ten fresh osteochondral disks were quantitatively measured before and after artificially induced surface degradation by mechanical grinding. The following quantitative OCT parameters were determined with a precise control of the surface inclination up to an angle of 10 • using a step of 2 • : optical reflection coefficient (ORC), variation of surface reflection (VSR) along the surface profile, optical roughness index (ORI) and optical backscattering (OBS). It was found that non-perpendicularity caused systematic changes to all of the parameters. ORC was the most sensitive and OBS the most insensitive to the inclination angle. At the optimal perpendicular angle, all parameters could detect significant changes after surface degradation (p < 0.01), except OBS (p > 0.05). Nonsignificant change of OBS after surface degradation was expected since OBS reflected properties of the internal cartilage tissue and was not affected by the superficial mechanical degradation. As a conclusion, quantitative OCT parameters are diagnostically potential for characterizing the cartilage degeneration. However, efforts through a better

Morphometric grading of osteoarthritis by optical coherence tomography - An ex vivo study

“…Referencing to an averaged surface position may not adequately recreate the curvature of knee or stifle joint cartilage when it comes to the definition of the mean reference surface as for example recent data on the curvature of human femoral condyles revealed the average curvature to be 4.4 m −1 (range, min/max: −20.0 m −1 /27.2 m −1 ) . Also, non‐perpendicularity of the OCT beam to the cartilage surface may increase inaccuracy and challenge in‐vivo applicability …”

Pre-Osteoarthritis

“…Optical coherence tomography (OCT) provides an additional intra-articular imaging modality to diagnose minute degenerative changes, especially in the superficial cartilage, including high-resolution quantitative analysis of surface roughness. 67 , 68 …”

“…OCT is an intra-articular imaging modality with microscopic resolution to diagnose minute degenerative changes in cartilage, including high-resolution quantitative analysis of surface roughness. 67 , 68 , 82 In OCT, limited penetration of light in tissue can prevent detailed imaging of deep layers of thick human cartilage.…”

Analysis and compensation for the effect of the catheter position on image intensities in intravascular optical coherence tomography

“…2 In practice, however, the signal magnitude may not be dependent only on the tissue type but also on the position of the catheter with respect to the vessel wall, which causes nontissue-related effects on the IVOCT image intensities. 5,6 An example is given in Fig. 1.…”

“…To the best of our knowledge, only one study with respect to this issue on OCT image intensities has been reported which was about nonperpendicular incident light causing a significant variance in the measurement of the articular cartilage. 6 In the followup studies of the bioresorption progress of the BVS strut, the bias in light intensity caused by the eccentric catheter was claimed to be minimized with normalization by manual selecting reference regions. 20 Results from IVUS cannot be applied directly to IVOCT, due to the differences in physical properties between both modalities.…”