23Na MR Imaging at 7 T after Knee Matrix-associated Autologous Chondrocyte Transplantation: Preliminary Results

Purpose: To evaluate the feasibility of sodium 7-T magnetic resonance (MR) imaging in repaired tissue and native cartilage of patients after matrix-associated autologous chondrocyte transplantation (MACT) and compare results with delayed gadolinium-enhanced MR imaging of cartilage (dGEMRIC) at 3 T. Materials and Methods: Ethical approval was provided by the local ethics committee; written informed consent was obtained from all patients. Six women and six men (mean age, 32.8 year +/- 8.2 [standard deviation] and 32.3 years +/- 12.7, respectively) were included. Mean time between MACT and MR was 56 months +/- 28. A variable three-dimensional (3D) gradient-echo (GRE) dual-flip-angle technique was used for T1 mapping before and after contrast agent administration at 3 T. All patients were also examined at 7 T (mean delay, 70.5 days +/- 80.1). A sodium 23-only transmit-receive knee coil was used with the 3D GRE sequence. A statistical analysis of variance and Pearson correlation were applied. Results: Mean signal-to-noise ratio (SNR) was 24 in native cartilage and was 16 in transplants (P<.001). Mean sodium signal intensities normalized with the reference sample were 174 +/- 53 and 267 +/- 42 for repaired tissue in the cartilage transplant and healthy cartilage, respectively (P<.001). Mean postcontrast T1 values were 510 msec +/- 195 and 756 msec +/- 188 for repaired tissue and healthy cartilage, respectively (P=.005). Mean score of MR observation of cartilage repair tissue was 75 +/- 14. Association between postcontrast T1 and normalized sodium signal values showed a high Pearson correlation coefficient (R) of 0.706 (P=.001). A high correlation of R = 0.836 (P=.001) was found between ratios of normalized sodium values and ratios of T1 postcontrast values. Conclusion: With the modified 3D GRE sequence at 7 T, a sufficiently high SNR in sodium images was achieved, allowing for differentiation of repaired tissue from native cartilage after MACT. A strong correlation was found between sodium imaging and dGEMRIC in patients after MACT. (C) RSNA, 2010