An open 8-channel parallel transmission coil for static and dynamic 7T MRI of the knee and ankle joints at multiple postures.

PurposeWe present the initial in vivo imaging results of an open architecture eight-channel parallel transmission (pTx) transceive radiofrequency (RF) coil array that was designed and constructed for static and dynamic 7T MRI of the knee and ankle joints. MethodsThe pTx coil has a U-shaped dual-row configuration (200mm overall length longitudinally) that allows static and dynamic imaging of the knee and ankle joints at various postures and during active movements. This coil structure, in combination with B-1 shimming, allows flexible configuration of B-1 transmit profiles, with good homogeneity over 120-mm regions of interest. This coil enabled high-resolution gradient echo (e.g., 3D dual-echo steady state [DESS] and 3D multiecho data image combination [MEDIC]) and turbo spin echo (TSE) imaging (e.g., with proton density weighting [PDw], PDw with fat saturation, and T-1 and T-2 weightings) with local RF energy absorption rates well below regulatory limits. ResultsHigh-resolution 2D and 3D image series (e.g., 0.3mm in-plane resolution for TSE, 0.47mm isotropic for DESS and MEDIC) were obtained from the knee and ankle joints with excellent tissue contrast. Dynamic imaging during continuous knee and ankle flexion-extension cycles were successfully acquired. ConclusionThe new open pTx coil array provides versatility for high-quality static and dynamic MRI of the knee and ankle joints at 7T. Magn Reson Med 79:1804-1816, 2018. (c) 2017 International Society for Magnetic Resonance in Medicine.