Sodium imaging of the human knee cartilage with magnetic resonance at ultra high field: Development of a double frequency (1H/23Na) RF coil

Sodium Magnetic Resonance Imaging (MRI) is an attractive imaging technique for early detection of osteoarthritis, as sodium concentrations correlate with proteoglycan content. However sodium yields much less signal in human tissues compared to hydrogen: it has a very rapid transverse signal decay (T2) and rapid longitudinal relaxation (T1), low gyromagnetic ratio and much smaller concentration than hydrogen. Ultra High Field (UHF) 7T MRI systems play an essential role to enhance the SNR, to achieve sufficient spatial resolution and to obtain images with diagnostically relevant contrast. This work shows how to design, develop and test a dual-tuned proton/sodium surface radio-frequency coil for 7T UHF MRI systems.