Abstract
BackgroundThe evolution of cartilage degeneration is still not fully understood, partly due to its thinness, low radio-opacity and therefore lack of adequately resolving imaging techniques. X-ray phase-contrast imaging (X-PCI) offers increased sensitivity with respect to standard radiography and CT allowing an enhanced visibility of adjoining, low density structures with an almost histological image resolution. This study examined the feasibility of X-PCI for high-resolution (sub-) micrometer analysis of different stages in tissue degeneration of human cartilage samples and compare it to histology and transmission electron microscopy.MethodsTen 10%-formalin preserved healthy and moderately degenerated osteochondral samples, post-mortem extracted from human knee joints, were examined using four different X-PCI tomographic set-ups using synchrotron radiation the European Synchrotron Radiation Facility (France) and the Swiss Light Source (Switzerland). Volumetric datasets were acquired with voxel sizes between 0.7 × 0.7 × 0.7 and 0.1 × 0.1 × 0.1 µm3. Data were reconstructed by a filtered back-projection algorithm, post-processed by ImageJ, the WEKA machine learning pixel classification tool and VGStudio max. For correlation, osteochondral samples were processed for histology and transmission electron microscopy.ResultsX-PCI provides a three-dimensional visualization of healthy and moderately degenerated cartilage samples down to a (sub-)cellular level with good correlation to histologic and transmission electron microscopy images. X-PCI is able to resolve the three layers and the architectural organization of cartilage including changes in chondrocyte cell morphology, chondrocyte subgroup distribution and (re-)organization as well as its subtle matrix structures.ConclusionsX-PCI captures comprehensive cartilage tissue transformation in its environment and might serve as a tissue-preserving, staining-free and volumetric virtual histology tool for examining and chronicling cartilage behavior in basic research/laboratory experiments of cartilage disease evolution.
Highlights
The evolution of cartilage degeneration is still not fully understood, partly due to its thinness, low radio-opacity and lack of adequately resolving imaging techniques
Multiscale X‐PCI‐computed tomography (CT) for hierarchical imaging of cartilage: Variation of spatial resolutions X-ray phase-contrast imaging (X-PCI)-CT images of cartilage samples acquired at three different spatial resolutions provide a detailed depiction of cartilage structures at different magnifications and fields of view
Overview of the cartilage architecture and chondrocyte arrangement Sagittal X-PCI-CT data reconstructions acquired with a voxel size of 6.1 × 6.1 × 6.1 μm3 provide an overview of Tissue degradation signs, such as superficial defects, their in-depth spread, and concomitant tissue architecture alterations with disturbances of the matrix, chondrocyte arrangement and even changes in morphology are directly visualized (Fig. 2B)
Summary
The evolution of cartilage degeneration is still not fully understood, partly due to its thinness, low radio-opacity and lack of adequately resolving imaging techniques. MRI techniques reach spatial resolutions down to 0.4 × 0.4 × 0.4 mm using isotropic 3D sequences These resolutions provide proper depiction of medium to advanced cartilage changes, but are only partly sufficient to reveal early tissue disturbances such as softening and superficial fibrillation; cellular cartilage components are not resolved. While morphological MRI is limited by satisfactory spatial and contrast resolutions, quantitative MRI techniques for analyzing cartilage matrix composition (collagen/proteoglycan content), such as delayed gadolinium-enhanced MRI of cartilage, sodium imaging [10] or T2 relaxation time mapping [11], have not been established in routine examinations because of their time-consuming acquisition, post-processing and resultant low resolution map of matrix changes
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