Correlations between X-ray attenuation and GAG content of different cartilage layers based on contrast agent enhanced Micro-CT

Objectives: To build the quantitative relationships between X-ray attenuation and glycosaminoglycan (GAG) content of different layers of progressive trypsin digested articular cartilage (AC) models based on the contrast agent enhanced Micro-CT. Methods: Bovine AC samples were treated with 0.5% concentration of trypsin for different degeneration time, immersed in contrast agent and then scanned by Micro-CT to obtain the X-ray attenuation. Combining with histological analysis, the relationships between the X-ray attenuation and GAG optical density of the superficial and middle layer were analyzed. Results: The X-ray mean attenuation increased about 16.48% (p<0.01) in the superficial layer within the first 10-minute degeneration, 26.99% (p<0.05) in the middle layer within the first 40-minute degeneration, but merely changed in the deep layer in the entire experiment. Contrary to the change of X-ray mean attenuation, the GAG optical density decreased from 31.98±13.00 to 11.69±4.23 (p<0.01) in the superficial layer within the first 10-minute degeneration, from 82.94±7.35 to 3.85±3.31 (p<0.01) in the middle layer within the entire degeneration and didn't slightly decrease from 96.10±2.50 to 91.45±1.90 (p<0.05) until the last 10-minute degeneration in deep layer. In addition, the changes of the X-ray mean attenuation showed negative linear correlations with the GAG content in the superficial (r = -0.984, p<0.01) and the middle layer (r = -0.960, p<0.01), respectively. Conclusion: The contrast agent enhanced Micro-CT can elucidate the variation of GAG content in trypsin-induced progressive AC models by X-ray mean attenuation of different cartilage layers.