Optimisation of intra-articular contrast agent and acquisition parameters for contrast-enhanced microCT of the mouse knee.

Abstract

Micro-computed tomography (microCT) is the gold standard for quantitative assessment of bone microstructure but provides limited contrast for articular cartilage due to its low X-ray attenuation. Ionic contrast agents offer a practical approach for enhancing cartilage-related contrast in absorption-based microCT; however, optimisation is required to enable reliable imaging of the murine knee joint while maintaining compatibility with bone morphometry. This study aimed to identify a practical contrast-enhanced microCT protocol for in situ imaging of the mouse knee through sequential optimisation of contrast agent, injection volume, and acquisition parameters that would be suitable for future planned in vivo studies. Fresh cadaver mice were used for protocol development. Two commercially available anionic gadolinium-based contrast agents (Dotarem and Magnevist) were first compared using intra-articular injection. Dotarem produced a significant increase in joint-space attenuation relative to contralateral controls, whereas Magnevist showed no measurable effect. Subsequent comparison of two Dotarem injection volumes showed that 7 μl produced a greater increase in joint space attenuation than 10 μl relative to controls. Acquisition parameters were then evaluated using multiple protocol-energy combinations. Lower tube voltages increased contrast but introduced saturation artefacts and inflated bone thickness measurements. Imaging at 70 kV provided the most consistent bone morphology while preserving contrast-enhanced joint space visualisation. Among the tested protocols, imaging at 70 kV, 114 μA, 1000 projections, and 200 ms integration time provided the most practical balance between image quality and scan duration. Together, this study identifies a practical contrast-enhanced microCT protocol for the in situ mouse knee that enhances joint-space contrast while maintaining compatibility with quantitative bone morphometry, providing a basis for future preclinical studies of osteoarthritis.