Sodium Mri of Articular Cartilage with Improved Snr Using Coherent Ssfp Imaging at 7t

PURPOSE: Sodium (Na) MRI offers direct information on the glycosaminoglycan concentration in cartilage. In vivo Na-MRI, however, is very challenging because of low Na sensitivity, low tissue concentration, and short biexponential transverse relaxation times (T2). Sequences capable of maximizing signal-to-noise ratio (SNR) are therefore highly desirable. Many groups addressed this issue by developing ultra-short echo time sequences (UTE) with TE<1ms, or by using Cartesian spoiled gradient echo (SPGR) sequences with very short TR. Although coherent steady state free precesion (SSFP) sequences, such as FISP or TrueFISP, provide higher SNR than SPGR, to our best knowledge, they have not yet been investigated for in vivo Na-MRI of cartilage. Thus, the aim of this study was to assess optimal in vivo measurement parameters for FISP and TrueFISP, and to evaluate their possible SNR gain as compared to SPGR in the human knee at 7T.