Cartilage Imaging using HR Propagation-Based Phase-contrast CT in a Guinea Pig Knee Joint Model of Different Age Groups

Introduction: Novel X-ray–based high-resolution propagation-based phase-contrast imaging computed tomography (PBI-CT) is a technique utilizing the dual property of X-rays passing through tissue. It provides contrast information about tissue architecture by using the proportional larger refraction signal by phase shifts that arise at tissue borders, even when its absorption contrast differences are imperceptible. Given this ability, the goal of our study was to evaluate the feasibility of PCI-CT in depicting hyaline cartilage in guinea pig knee joints of different age groups and compare it with micro-CT.

Materials and Methods: We examined the ex vivo knee joint of three guinea pigs (Hartley strain) ages 9, 15, and 21 months using PBI-CT at the European Synchrotron Radiation Facility in Grenoble, France (biomedical beamline ID17, collimated X-ray beam 52 keV, field of view 60 mm², resolution 46 × 46 µm²) and a conventional absorption-based micro-CT, typically used for small animal CT imaging (GE, Phoenix X-ray; same resolution of 46 × 46 µm²). Phase retrieved PBI-CT images were reconstructed sagittally by using the filtered back projection algorithm and equally sloped tomography and compared with corresponding conventional micro-CT data sets. The femoral and tibial cartilage were manually segmented and color coded for improved visualization.

Results: PBI-CT shows superior visualization of the guinea pig femoral and tibial cartilage layers compared with the absorption-based conventional micro-CT that was acquired with the same resolution. The original data sets show no differences between the cartilage plates of the guinea pigs of different age groups. However, after application of a color map, differences in electron densities of the cartilage plates of the different age groups were depictable.

Conclusion: PBI-CT provides improved cartilage depiction compared with conventional absorption-based micro-CT. Color mapping enables highlighting differences in the cartilage structure of aging cartilage in a small animal model such as in guinea pigs. Given this ability of PCI-CT in depicting differences in such small structures, it may be a promising technique for future cartilage imaging studies in small animal models.