In vivo bone and cartilage MRI using fully‐balanced steady‐state free‐precession at 7 tesla

The purpose of this work was to investigated the feasibility of fully-balanced steady-state free-precession (bSSFP) pulse sequence for trabecular bone and knee cartilage imaging in vivo using ultra-high-field (UHF) MRI at 7T in comparison with pulse sequences previously used at 3T. We showed that bSSFP and spin-echo imaging is possible at higher field strengths within 3.2 W/kg specific absorption rate (SAR) constraints. All pulse sequences were numerically optimized based on measured tissue relaxation parameters from six healthy volunteers (T(1) = 820 +/- 128 ms, T(2) = 43.5 +/- 3 ms for bone marrow and T(1) = 1745 +/- 104 ms and T(2) = 30 +/- 4 ms for cartilage). From simulations of the Bloch equation, a signal-to-noise ratio (SNR) increase of more than 1.9 was predicted. Cartilage SNR of bSSFP was 2.4 times higher at 7T (51.3 +/- 4.3) compared with 3T (21.3 +/- 3.3). Bone SNR increased from 11.8 +/- 2.0 to 13.2 +/- 2.5 at the higher field strength. We concluded that there is SNR benefit and great potential for bone and cartilage imaging at higher field strength.