Evaluation of cartilage repair tissue after biomaterial implantation in rat patella by using T2 mapping

Abstract

To evaluate the ability of MR T2 mapping (8.5 T) to characterize ex vivo longitudinally, morphologically and quantitatively, alginate-based tissue engineering in a rat model of patellar cartilage chondral focal defect. Calibrated rat patellar cartilage defects (1.3 mm) were created at day 0 (D0) and alginate sponge with (Sp/C+) or without (Sp/C-) autologous chondrocytes were implanted. Animals were sacrificed sequentially at D20, D40 and D60 after surgery and dissected patellae underwent MRI exploration (8.5 T). T2 values were calculated from eight SE images by using nonlinear least-squares curve fitting on a pixel-by-pixel basis (constant repetition time of 1.5 s, eight different echo times: 5.5, 7.5, 10.5, 12.5, 15.0, 20.0, 25.0 and 30.0 ms). On the T2 map, acquired in a transversal plane through the repair zone, global T2 values and zonal variation of T2 values of repair tissue were evaluated versus control group and compared with macroscopic score and histological studies (toluidine blue, sirius red and hematoxylin-eosin). "Partial", "total" and "hypertrophic" repair patterns were identified. At D40 and D60, Sp/C+ group was characterized by a higher proportion of "total" repair in comparison to Sp/C- group. At D60, the proportion of "hypertrophic" repair was two fold in Sp/C- group versus Sp/C+ group. As confirmed morphologically and histologically, the T2 map also permitted the distinction of three types of repair tissue: "total", "partial" and "hypertrophic". "Total" repair tissue was characterized by high T2 values versus normal cartilage (p<0.05). Zonal variation, reflecting the collagen network organization, appeared only at D60 for Sp/C+ group (p<0.05). "Hypertrophic" tissue, mainly observed at D60, presented high T2 global values without zonal variation with cartilage depth. These results confirm the potency of the MR T2 map (8.5 T) to characterize macroscopically and microscopically the patterns of the scaffold guided-tissue repair of a focal chondral lesion in the rat patella ("total", "partial" and "hypertrophic"). On T2 map, three parameters (i.e. MRI macroscopic pattern, T2 global values and zonal variation of T2 values) permit to characterize chondral repair tissue, as a virtual biopsy.

Quantitative T2 mapping during follow‐up after matrix‐associated autologous chondrocyte transplantation (MACT): Full‐thickness and zonal evaluation to visualize the maturation of cartilage repair tissue

“…Our study results are compatible with the maturation process of cartilage repair tissue as shown by WatrinPinzano et al, 12 which has recently been demonstrated in humans in an initial pilot study with preliminary results. Watrin-Pinzano et al 12 first described the ability of MR T2 mapping to characterize cartilage maturation longitudinally in an ex vivo rat model at 8.5 Tesla.…”

“…Watrin-Pinzano et al 12 first described the ability of MR T2 mapping to characterize cartilage maturation longitudinally in an ex vivo rat model at 8.5 Tesla. Animals were sacrificed at different time points after cartilage repair with biomaterial implantation, and MRI was compared to the histological assessment.…”

“…11 In cartilage repair tissue, histologically validated animal studies report this increase in zonal T2 as an indicator of hyaline or ''hyaline-like'' cartilage composition. 12,13 The aim of this study was to evaluate if in vivo mean (full-thickness) as well as zonal (deep and superficial) quantitative T2 assessment in patients after MACT is capable to visualize the maturation of the cartilage repair tissue.…”

Characterization of Engineered Cartilage Constructs Using MultiexponentialT2Relaxation Analysis and Support Vector Regression

“…1,[28][29][30] Recent work has explored tissue compartments within cartilage using multiexponential transverse relaxation analysis 7,13,31 and has applied multivariate statistical techniques to characterize and grade cartilage. 15,32 The current study combined these two approaches by developing SVR models from tissue compartment characteristics.…”

Monitoring Tissue Engineering Using Magnetic Resonance Imaging

“…An example of the changes in T 2 observed is shown in Figure 4 Progress in monitoring tissue-engineered cartilage in vivo -MRI techniques have also been used in vivo to characterize the development of tissue engineered cartilage (58], [59,60). In a study by Watrin-Pinzano and coworkers (58), MR was used to generate T 2 maps during the repair of a focal patellar cartilage defect in a rat. In this study, alginate scaffolds, with and without autologous chondrocytes, were implanted at day 0 to repair rat patellar cartilage defects.…”