Fig. 4.

Sagittal T2-weighted 7-T MR image (left panel) of the right knee demonstrating an attempted microfracture (bracket) at the anterior aspect of the lateral femoral condyle. Synovial fluid is seen at the articular surface (arrows). On the conventional ²³Na map (middle panel), hyperintense signal is seen from the synovial fluid at the articular surface. On the ²³Na-IR maps (right panel), there is suppression of signal from synovial fluid. The sodium images represent concentration maps with coloured bars indicating range of [Na⁺] in mM (red=600 mM, blue=0 mM). The larger apparent joint space size on sodium maps compared with the proton images is likely due to partial volume averaging from the lower resolution of the sodium maps (2 mm×2 mm×2 mm vs 0.546 mm×0.546 mm×2 mm)