Optical Coherence Tomography (OCT) yields microscopic cross-sectional images of cartilage in real time and at high resolution. As yet, comprehensive grading of degenerative cartilage changes based on OCT has rarely been performed. This study investigated the potential of quantitative OCT using algorithm-based image parameters such as irregularity (OII -Optical Irregularity Index), homogeneity (OHI -Optical Homogeneity Index) and attenuation (OAI -Optical Attenuation Index) in the objective grading of cartilage degeneration. Therefore, OCT was used to image and assess 113 human osteochondral samples obtained from total knee replacements. Processing included the analysis of OII (by calculation of the standard deviation with regards to a fitted surface), of OHI (by edge detection of tissue signal changes) and of OAI (by analysis of relative imaging depth). Additionally, samples were subject to macroscopic (Outerbridge grading), biomechanical (elastic stiffness), qualitative OCT and histological evaluation (Modified Mankin grading). Significant correlations were found between all outcome measures. OII and OHI were effective in assessing cartilage surface, integrity and homogeneity, while OAI could discriminate between unmineralized and mineralized cartilage, respectively. Therefore, quantitative OCT holds potential as a diagnostic tool for more reliable, standardized and objective assessment of cartilage tissue properties. ß
Optical Coherence Tomography (OCT) is an evolving imaging technology allowing non-destructive imaging of cartilage tissue at near-histological resolution. This study investigated the diagnostic value of real time 3-D OCT in comparison to conventional 2-D OCT in the comprehensive grading of human cartilage degeneration. Fifty-three human osteochondral samples were obtained from eight total knee arthroplasties. OCT imaging was performed by either obtaining a single two-dimensional cross-sectional image (2-D OCT) or by collecting 100 consecutive parallel 2-D OCT images to generate a volumetric data set of 8 Â 8 mm (3-D OCT). OCT images were assessed qualitatively according to a modified version of the DJD classification and quantitatively by algorithm-based evaluation of surface irregularity, tissue homogeneity, and signal attenuation. Samples were graded according to the Outerbridge classification and statistically analyzed by one-way ANOVA, Kruskal Wallis and Tukey's or Dunn's post-hoc tests. Overall, the generation of 3-D volumetric datasets and their multiple reconstructions such as rendering, surface topography, parametric, and cross-sectional views proved to be of potential diagnostic value. With increasing distance to the mid-sagittal plane and increasing degeneration, score deviations increased, too. In conclusion, 3-D imaging of cartilage with image analysis algorithms adds considerable potential diagnostic value to conventional OCT diagnostics. ß
We report a method of high-speed phase contrast and bright field microscopy which permits large cell culture vessels to be scanned at much higher speed (up to 30 times faster) than when conventional methods are used without compromising image quality. The object under investigation moves continuously and is captured using a flash illumination which creates an exposure time short enough to prevent motion blur. During the scan the object always stays in focus due to a novel hardware-autofocus system.
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