Assessment of articular cartilage using optical coherence tomography and high frequency ultrasound

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Assessment of articular cartilage using optical coherence tomography and high frequency ultrasound


Author: Wang, Shuzhe
Title: Assessment of articular cartilage using optical coherence tomography and high frequency ultrasound
Degree: M.Phil.
Year: 2009
Subject: Hong Kong Polytechnic University -- Dissertations.
Articular cartilage -- Imaging.
Optical coherence tomography.
Ultrasonic imaging.
Department: Dept. of Health Technology and Informatics
Pages: xxiii, 193 p. : ill. ; 30 cm.
Language: English
InnoPac Record:
Abstract: Articular cartilage is a thin complex tissue covering the bony ends of joints. Optical coherence tomography (OCT) has recently attracted researchers' attention for the assessment of articular cartilage due to its characteristics of having miniaturized probe and high resolution and being non-contact. However, little has been reported on the basic characteristics of articular cartilage determined using OCT. High frequency ultrasound has also been a useful tool to assess the condition of articular cartilage. Little systematical study has been done, however, to investigate the relationships between morphological, acoustic and mechanical properties of articular cartilage. No study has been reported to use both OCT and ultrasound simultaneously for the assessment of articular cartilage. In this study, an OCT system with a central wavelength of 1310 nm was employed to investigate the refractive index (RI), OCT roughness index (ORI), and stiffness of cartilage. A high frequency ultrasound system (55 MHz) and an ultrasound water jet indentation system (20 MHz) were also used to measure the ultrasound roughness index (URI), acoustic parameters, thickness, and stiffness of cartilage. In the experiment of the depth and degeneration dependences of RI assessment, articular cartilage plugs were collected from bovine patella (n=18). The cartilage layer was further prepared into two halves and three horizontal cartilage slices (n=l8x2x3) with an approximately equal thickness. Forty samples for surface roughness, acoustic parameters, thickness and mechanical properties measurements were prepared from twenty bovine patellae (n=20x2). The enzymes, collagenase and trypsin, were applied to remove the collagen fibrils and proteoglycans in cartilage, respectively, to simulate cartilage degeneration. It was found that the RI was significantly different among the three layers for both normal and enzyme-treated articular cartilage, while the enzyme treatments didn't lead to a significant change. Both ORI and URI results showed significant increase of roughness index in the collagenase digestion group. No significant difference was observed in the trypsin digestion group. The results of mechanical properties of articular cartilage showed that stiffness reduced significantly in both enzyme treatment groups. Histological analysis revealed that most of the proteoglycans were depleted after the trypsin digestion. Images of scanning electron microscopy (SEM) suggested a degradation of cartilage surface after the collagenase digestion. A linear relationship was observed between ORI and URI results. Stiffness measured by both air jet and water jet indentation tests showed linear relationships with the stiffness and Young's modulus obtained by standard mechanical indentation tests. A linear relationship was noted between the integrated reflection coefficient (IRC) and URI. Inverse and power relationships were noted between stiffness and roughness index in the collagenase treatment group. In summary, OCT and ultrasound could be useful tools to investigate the optical (OCT), acoustic (ultrasound), morphological, and mechanical properties of articular cartilage quantitatively. The combination of these two techniques may provide a comprehensive assessment of articular cartilage. Future studies are needed to further investigate properties of cartilage from different sites and species. The studies of quantitative assessments of cartilage properties in vivo using endoscope-based OCT and ultrasound are also necessary in the future.

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