Rapid isotropic 3D-sodium MRI of the knee joint in vivo at 7T

Purpose: To demonstrate the feasibility of acquiring high-resolution, isotropic 3D-sodium magnetic resonance (MR) images of the whole knee joint in vivo at ultrahigh field strength (7.0T) via a 3D-radial acquisition with ultrashort echo times and clinically acceptable acquisition times. Materials and Methods: Five healthy controls (four males, one female; mean ± standard deviation [SD] age 28.7 ± 4.8 years) and five patients with osteoarthritis (OA) (three males, two females; mean ± SD age 52.4 ± 5.6 years) underwent ²³Na MRI on a 7T, multinuclei equipped whole-body scanner. A quadrature ²³Na knee coil and a 3D-gradient echo (GRE) imaging sequence with a radial acquisition were utilized. Cartilage sodium concentration was measured and compared between the healthy controls and OA patients. Results: The average signal-to-noise ratio (SNR) for different spatial resolutions (1.2-4 mm) varied from ∼14-120, respectively. The mean sodium concentration of healthy subjects ranged from ∼240 ± 28 mM/L to 280 ± 22 mM/L. However, in OA patients the sodium concentrations were reduced significantly by ∼30%-60%, depending on the degree of cartilage degeneration. Conclusion: The preliminary results suggest that sodium imaging at 7T may be a feasible potential alternative for physiologic OA imaging and clinical diagnosis.