Evaluation of Extended and Shielded Monopole Antenna Array (ESMA) at 7T

INTRODUCTION: By modifying the monopole antenna array (MA) for whole brain imaging, we developed extended and shielded monopole antenna array (ESMA) in order to enhance the uniformity of imaging at 7T MRI application. We compared the performance of this new coil with two different types of coils, namely, MA and extended monopole antenna array (EMA). The three coil types were evaluated for the transmit properties, the signal to noise ratio (SNR), and receiver sensitivity. METHODS: All imaging tests were performed on the investigational 7T MRI scanner (Siemens Medical Solutions, Erlangen, Germany) with a magnet bore of 90 cm (Magnex Scientific, Abingdon, UK). All the coils were tuned to 297.2 MHz (7T) with a human head loading. Fig. 1 shows the schematics and photos of the three coils: 8-ch MA (Fig. 1a, d), 8-ch EMA (Fig. 1b, e) and 8-ch ESMA (Fig. 1c, f). Ceramic capacitors (330 pF) were connected across each divided ground plane to minimize the eddy current. Eight equally spaced monopoles were mounted orthogonal to the ground plane, forming a circle along the acrylic pipe connected to the ground plane [1]. For the ESMA (Fig. 1c, f), a thin layer copper tape was attached to the acrylic boxes and served as the individual shields [2]. Each shield was positioned to start 2cm away from the feeding point and end 0.5 cm past the ending of the monopole. Each channel was located at the center of the acrylic boxes of 5x23x3.5 cm. Each monopole was placed 2cm away from the wall [3]. The MA