A dedicated two-element phased array receiver coil for high resolution MRI of rat knee cartilage at 7T

Despite that on clinical systems phased array technology is now widely used, the high field MRI experimental systems with multiple receiver channels just became available few years ago. For this reason and due to the large range of magnetic field (frequencies between 200 and 500 MHz for proton resonance), commercial phased arrays implemented in narrow bore for high field applications are rare and relatively expensive. Array coil imaging is an advanced method for acquiring high resolution images with enhanced signal-to-noise ratio (SNR) and/or enlarged field of view (FOV) compared for example to single loop surface coil. The volume of interest is then covered by several coil elements and images reconstructed for every single channel are combined afterwards. The goal of this work was to develop a dedicated two-element array coil operating at 300 MHz (7 T) for high-resolution imaging of rat knee joint in order to quantify cartilage thickness and volume. A dedicated two-element array coil with two square elements encompassing knee joint was designed and built. Decoupling between elements was achieved with a capacitor inserted on the common leg of the two elements. The average gain in SNR compared to a 15 mm reference single loop coil was 2.2. This SNR gain was used to improve spatial resolution of 3D acquisition by decreasing the voxel size from 59 x 59 x 156 mum³ to 51 x 51 times 94 mum³ without time penalty. This two element array coil is a key element to perform HR-MRI and extract morphological parameters of animal cartilage. Finally, a set of two array coils were used to perform the acquisition of both rat knee joint at the same time with no additional acquisition time or resolution decrease.