In vivo sodium imaging of human patellar cartilage with a 3D cones sequence at 3 T and 7 T

Purpose: To compare signal-to-noise ratios (SNRs) and T ₂* maps at 3 T and 7 T using 3D cones from in vivo sodium images of the human knee. Materials and Methods: Sodium concentration has been shown to correlate with glycosaminoglycan content of cartilage and is a possible biomarker of osteoarthritis. Using a 3D cones trajectory, 17 subjects were scanned at 3 T and 12 at 7 T using custom-made sodium-only and dual-tuned sodium/proton surface coils, at a standard resolution (1.3 x 1.3 x 4.0 mm ³) and a high resolution (1.0 x 1.0 x 2.0 mm ³). We measured the SNR of the images and the T ₂* of cartilage at both 3 T and 7 T. Results: The average normalized SNR values of standard-resolution images were 27.1 and 11.3 at 7 T and 3 T. At high resolution, these average SNR values were 16.5 and 7.3. Image quality was sufficient to show spatial variations of sodium content. The average T ₂* of cartilage was measured as 13.2 ± 1.5 msec at 7 T and 15.5 ± 1.3 msec at 3 T. Conclusion: We acquired sodium images of patellar cartilage at 3 T and 7 T in under 26minutes using 3D cones with high resolution and acceptable SNR. The SNR improvement at 7 T over 3 T was within the expected range based on the increase in field strength. The measured T ₂* values were also consistent with previously published values.