Cartilage Engineering and MRI: Assessment of Biointegration and Biofunctionality in the Rat – CEMABIR

Early diagnosis of chondral lesions needs development and validation of imaging tools permitting a qualitative and quantitative evaluation of articular cartilage. Nowadays, MRI appears as a promising tool, allowing a precise multiplanar exploration of hyaline cartilage. Recent improvement of acquisition parameters (gradient, matrix size, dedicated smaller coils, new faster acquisition modalities) makes now possible morphologic evaluation of articular cartilage in small joints, with a good spatial and tissular resolutions for various articular components. MR evaluation depicts chondral lesions, but also concomitant articular inflammatory events, ligamentous lesions, subchondral bone oedema, and possible associated articular (e.g. menisci, capsule) lesions. Clinical MR evaluations (volumetric or biochemical through T1 or T2 mapping) have been mainly validated in the human knee due to the easy accessibility of this joint to dedicated coils and to the importance of femorotibial joint cartilage thickness. On the other hand, the accuracy of MRI in cartilage healing remains to be established. This non invasive technique is sensitive, but variable, in tissular cartilage healing characterization. In addition there is no international consensus concerning a routine gold standard acquisition modality for cartilage engineering. Nevertheless, T2 mapping seems promising as a good asset as recently published. A preclinical validation in an experimental model seems thus necessary to validate its accuracy versus other imaging modalities. We have previously validated ex vivo the sensitivity of T2 mapping in cartilage engineering of the rat patella. Recent works are concordant in the horse. To date, there is no published in vivo work concerning cartilage engineering in the rat. Recent in vivo data ('Imagerie du Petit Animal' program) suggest that high field MRI (7T) may be useful in morphologic analysis of normal and OA cartilage rat femorotibial cartilage (cartilage thickness and volume). The aim of this project is to evaluate in vivo the high field MR accuracy (7T) to appreciate, in the nude rat knee, the bio-integration and bio-functionality of a composite chondral implant (human mesenchymal stem cells and type I collagen sponge) during an experimental model of focal chondral lesion. We have previously established the feasibility of in vivo MR assessment of the rat knee at 7T. In this project the main steps consist in: # optimizing good laboratory practices for obtaining the composite chondral implant # defining the best experimental conditions in inducing the focal defect and following its spontaneous cicatrisation and facilitated regeneration in the rat knee # evaluating the accuracy for cartilage engineering of various acquisitions procedures (dedicated coils or sequences like 3D SPGR, MR arthrography) and signal processing (T2 maps, T2* with ferromagnetic particles, thickness and surface mapping) # confronting each acquisition with histological results. These data will facilitate the pre-requisites of a future clinical transfert in the field of autologous cartilage transplantation and MSC based articular engineering.