Quantitative magnetic resonance imaging (MRI) assessments such as T2 mapping have been recently studied to detect the biochemical composition and structure of articular cartilage. In the present study, we investigated the correlation of zonal image of T2 mapping MRI of the repair cartilage with the histology of biopsy specimen at the corresponding area in five patients who underwent the implantation of a scaffold-free tissue-engineered construct (TEC) generated from autologous synovial mesenchymal stem cells (MSCs) to an isolated cartilage lesions, and aim to elucidate the efficacy and limitation of T2 mapping MRI for the evaluation of cartilage repair.
We performed both T2 mapping MRI and histological evaluation of biopsy specimen at the identical area in all patients at 48 weeks postoperatively, and T2 values and histological scores were compared at superficial, middle and deep zone of repair tissue.
Histology showed that the repair tissue in the superficial zone was dominated by fibrous tissue and the ratio of hyaline-like matrix increased with the depth of the repair tissue, leading to the dominance by hyaline cartilage–like tissue in the deep zone (Figure 1). There was significant difference between superficial and middle/deep zones in histological scores. Conversely, there was no statistical significances in T2 value detected among zones (Figure 2). Accordingly, there were no correlations detected between histological scores and T2 values in each zone.
Such discrepancy of the data between T2 mapping and histology suggests that T2 mapping failed in detecting the collagen architecture and composition of repair cartilage. This suggests that the resolution of current quantitative MRI might not be enough to depict the difference in zonal collagen architecture in repair cartilage. Furthermore, although invasive, histologic assessment is likely still more reliable method for evaluation of tissue quality.