The objective of the present study was to validate the ability of Equilibrium Partitioning of an Ionic Contrast agent via microcomputed tomography (EPIC-μCT) to nondestructively assess cartilage morphology in the rat model.

An appropriate contrast agent (Hexabrix) concentration and incubation time for equilibration were determined for reproducible segmentation of femoral articular cartilage from contrast-enhanced μCT scans. Reproducibility was evaluated by triplicate scans of six femora, and the measured articular cartilage thickness was independently compared to thickness determined from needle probe testing and histology. The validated technique was then applied to quantify age-related differences in articular cartilage morphology between 4, 8, and 16-week-old (n=5 each) male Wistar rats.

A 40% Hexabrix/60% phosphate buffered saline (PBS) solution with 30min incubation was optimal for segmenting cartilage from the underlying bone tissue and other soft tissues in the rat model. High reproducibility was indicated by the low coefficient of variation (1.7–2.5%) in cartilage volume, thickness and surface area. EPIC-μCT evaluation of thickness showed a strong linear relationship and good agreement with both needle probing (r²=0.95, slope=0.81, P<0.01, mean difference 11±22μm, n=43) and histology (r²=0.99, slope=0.97, P<0.01, mean difference 12±10μm, n=30). Cartilage volume and thickness significantly decreased with age while surface area significantly increased.

EPIC-μCT imaging has the ability to nondestructively evaluate three-dimensional articular cartilage morphology with high precision and accuracy in a small animal model.