Improved assessment of cartilage repair tissue using fluid-suppressed 23Na inversion recovery MRI at 7 Tesla: preliminary results

To evaluate cartilage repair and native tissue using a three-dimensional (3D), radial, ultra-short echo time (UTE) 23Na MR sequence without and with an inversion recovery (IR) preparation pulse for fluid suppression at 7 Tesla (T). This study had institutional review board approval. We recruited 11 consecutive patients (41.5 ± 11.8 years) from an orthopaedic surgery practice who had undergone a knee cartilage restoration procedure. The subjects were examined postoperatively (median = 26 weeks) with 7-T MRI using: proton-T2 (TR/TE = 3,000 ms/60 ms); sodium UTE (TR/TE = 100 ms/0.4 ms); fluid-suppressed, sodium UTE adiabatic IR. Cartilage sodium concentrations in repair tissue ([Na+]R), adjacent native cartilage ([Na+]N), and native cartilage within the opposite, non-surgical compartment ([Na+]N2) were calculated using external NaCl phantoms. For conventional sodium imaging, mean [Na+]R, [Na+]N, [Na+]N2 were 177.8 ± 54.1 mM, 170.1 ± 40.7 mM, 172.2 ± 30 mM respectively. Differences in [Na+]R versus [Na+]N (P = 0.59) and [Na+]N versus [Na+]N2 (P = 0.89) were not significant. For sodium IR imaging, mean [Na+]R, [Na+]N, [Na+]N2 were 108.9 ± 29.8 mM, 204.6 ± 34.7 mM, 249.9 ± 44.6 mM respectively. Decreases in [Na+]R versus [Na+]N (P = 0.0.0000035) and [Na+]N versus [Na+]N2 (P = 0.015) were significant. Sodium IR imaging at 7 T can suppress the signal from free sodium within synovial fluid. This may allow improved assessment of [Na+] within cartilage repair and native tissue. circle NaIR magnetic resonance imaging can suppress signal from sodium within synovial fluid. circle NaIR MRI thus allows assessment of sodium concentration within cartilage tissue alone. circle This may facilitate more accurate assessment of repair tissue composition and quality. (orig.)