Early research in phase-contrast imaging indicates that substantial higher soft-tissue contrast resolution can be obtained compared with conventional absorption radiography. In the present feasibility study, we used the phase contrast analyzer-based technique in tomographic mode to investigate whether structural cartilage matrix properties can be depicted in an ex vivo set-up and whether high resolution CT-phase contrast imaging may enable differentiation of osteoarthritic and intact cartilage matrixes.
Four postmortem osteochondral cylinders (7 mm diameter, 2 osteoarthritic, 2 healthy control samples from 4 human patellae) underwent tomographic phase-contrast analyzer-based imaging at high resolution (voxel size: 8(3) micron3) at 26 keV (European Synchrotron Radiation Facility, Grenoble, France). From the acquired data volumes, sets of reconstructed sagittal slices were selected at 0.5 mm increments from osteoarthritic and control specimens. Two independent, blinded observers assessed structural characteristics (cartilage thickness, topographic chondrocyte distribution homogeneity, zonal height, and surface damage) and differences between the 2 groups were determined.
Phase contrast analyzer-based CT showed excellent depiction of the complete volume and of the 3D architecture of the cartilage in all samples. A distinct zonal pattern in the cartilage matrix could consistently be visualized. The osteoarthritic samples showed significantly lower chondrocyte distribution homogeneity (0% vs. 76% homogeneous, P < 0.001), less chondrocyte alignment (0% vs. 59% fully aligned, P < 0.001), lower height of tangential, transitional, and radial zones (all P < 0.001) and a higher prevalence of superficial cartilage damage (84% vs. 10%, P < 0.001).
This first proof-of-concept study demonstrates that high resolution phase contrast CT visualizes structural details in relatively thick ex vivo cartilage samples. Our results suggest that the technique permits differentiation of osteoarthritic and healthy cartilage by enabling assessment of histologic characteristics of cartilage structures.