Quantitatively relating magnetic resonance <i>T</i>₁ and <i>T</i>₂ to glycosaminoglycan and collagen concentrations mediated by penetrated contrast agents and biomacromolecule-bound water.

"Conflicts of interest statement . The authors declare no competing interests."

"The work was financially supported by National Natural Science Foundation of China (grant no. 52130302). We sincerely thank Prof. Maili Liu, Prof. Ping Zhou, Prof. Heyong He, Prof. Peiyi Wu and Dr. Guijin Li for the helpful discussion of the work and/or a critical reading of the manuscript. This work has established the definite relations of MR indexes T1 and T2 to the contents of the two main biomacromolecules in cartilage ECM based on ‘clean’ systems in vitro. The MRI signal in the biomacromolecule-water system is thought to be affected by the hydrogen proton of the biomacromolecule-bound water. In T2-weighted imaging, COL exhibited more significant effects on T2 relaxation than GAG, which has been interpreted from the fact that COL generates more the IBW and subsequently the OBW. GAG can regulate the distribution of the negatively charged gadolinium contrast agent in cartilage tissue owing to the charge effect and thus significantly affect T1-weighted imaging. In addition, this work reports the quantitative clinical analysis of MRI on the regeneration of human knee cartilage 18 months after MACI surgery. Through T2 mapping and dGEMRIC methods, the values of T2 and ΔR1 were found to decrease gradually at 3, 6 and 12 months after MACI, indicating the maturation of the COL network and the increase of the GAG content in the regenerated cartilage. This study affords one of the academic bases of MRI standards to evaluate cartilage regeneration in vivo in a real-time and non-invasive manner. The fundamental research has ever greatly supported the suggestion of an ISO standard by the Chinese team, which was approved as ISO/TS24560-1:2002 in September 2022."