Optimized MTL array with serial capacitors for 7T MRI

Transmit/receive MTL (Microstrip Transmission Line) array has been widely used for ultra-high-field MRI because of its low mutual coupling characteristics. However, several design issues such as limit to the length of a single coil element still remains. For traditional MTL coils, two capacitors (one fixed, one variable) were put at both ends of the coil element for tuning. Based on our experimental observations, the length of the traditional MTL element is limited at 7T MRI because of increased non-uniform distribution of B1 field along the Z direction. In this study, an optimized MTL array with six capacitors equally distributed along the strip line was investigated. The optimized MTL array can generate a more uniform B1 field along the Z direction compared with the traditional MTL array. The numerical investigation was performed using the RF circuit and 3-D EM co-simulation.