Shielded Microstrip Head Array at 7T

INTRODUCTION Microstrip transceiver arrays have been demonstrated to provide higher efficiency on signal excitation/reception and low mutual coupling and have become a popular RF solution to parallel MR imaging at ultrahigh fields in humans [1,2]. In most designs, the ground planes of microstrips are separated (Fig 1) to minimize their mutual coupling [1-5]. Practically, due to space limitations, the size of ground planes of the microstrip elements is usually not large enough to become a “true” ground, in which the condition of microstrip (an unbalanced transmission line) is not rigorously satisfied. Consequently, the transceiver array may suffer from cable resonance, lower Q factors and imaging quality degradations. This problem is more prominent in transceiver arrays with a large number of resonant elements. Symmetrical feeding [4] by inserting the tuning/matching circuit at the center of each microstrip can alleviate the cable-resonance problem, improving the coil’s stability despite some difficulties in performing on-site tuning/matching. In this work we present an approach to improving the performance of microstrip transceiver arrays by introducing RF shieldings outside the microstrip array and the feeding coaxial cables. With this improvement, reduced interaction among cables, better resonance stability, better Q-factors and thus improved imaging quality are achieved.