Contrast-Enhanced CT Imaging as a Non-Destructive Tool for Ex Vivo Examination of the Biochemical Content and Structure of the Human Meniscus

Abstract

Objective: Biochemical and biomechanical changes occur in the meniscus before osteoarthritis (OA) is clinically diagnosed through symptoms. However, existing techniques to characterize such changes are destructive and time-consuming. This study evaluated the ability of contrast-enhanced computed tomography (CECT) and contrast agent flux using the contrast agents Ioxaglate (ioxaglate) and CA4+ to correlate with the glycosaminoglycan (GAG) distribution and water content in ex vivo human menisci using microCT imaging. Methods: A diffusion-in kinetics study for CA4+ was conducted to determine the equilibrium time for the contrast agents by subregion. Subsequently, the optimal concentrations of Ioxaglate and CA4+ to map the native GAG distribution were determined. Then, these optimal concentrations were used to examine correlations between CECT attenuation and GAG content at various time points, including equilibrium time. Using microCECT imaging, imaged zones were excised, rinsed, and analyzed for GAG content by subregion using the dimethylmethylene blue (DMMB) assay. Depth-wise analysis was performed through each of the native surfaces to examine differences in contrast agent diffusion kinetics and calculate flux. Finally, correlations between CECT attenuation and GAG content, CECT attenuation and water content, and flux and water content were calculated by subregion and whole meniscus. Results: The equilibrium time was 48 hr with tau values ranging from 7.09 hr (posterior), 9.64 hr (anterior), and 12.32 hr (center). The optimal concentrations for native GAG mapping for ioxaglate and CA4+ were ≥80 mgI/mL and 12 mgI/mL, respectively. Using these optimal concentrations, weak to moderate correlations were found between ioxaglate CECT and GAG content at all diffusion time points, while strong correlations existed between CA4+ attenuation and GAG content as early as 7 hr (R2=0.67), strengthening by equilibrium (R2=0.81). CECT attenuation for both contrast agents did not significantly correlate with water content but CA4+ flux for the entire meniscus correlated moderately to strongly with water content (R2=0.56-0.64). Conclusions: CECT attenuation is a rapid, effective, non-destructive imaging technique to evaluate meniscal GAG distribution and water content. With CA4+ CECT, GAG content and distribution can be mapped in the human meniscus with high resolution. Consequently, CA4+ CECT is a useful tool for determining the biochemical health of human meniscal tissue, and further developments in quantitative imaging techniques will aid in understanding meniscal biology, diagnosis, and monitoring treatment outcomes.