High-Density MRI RF Arrays Using Mixed Dipole Antennas and Microstrip Transmission Line Resonators

Objective:
High-density multi-coil arrays are desirable in MRI because they provide high signal-to-noise ratios (SNR), enable highly accelerated parallel imaging, and provide more uniform transmit fields at high fields. For high-density arrays such as a head array with 16 elements in a row, popular dipole antennas and microstrip transmission line (also referred to as “MTL”) resonators both have severe coupling issues.
Methods:
In this work, we show that dipoles and MTLs have naturally low coupling and propose a novel array configuration in which they are interleaved. We first show the electromagnetic (EM) coupling between a single dipole and a single MTL across different separations in bench tests. Then we validate and analyze this through EM simulations. Finally, we construct a 16-channel mixed dipole and MTL array and evaluate its performance on the bench and through MRI experiments.
Results:
Without any decoupling treatments, the worst coupling between a dipole and an MTL was only −15.8 dB when their center-to-center distance was 4.7 cm (versus −5.4 dB for two dipole antennas and −6.0 dB for two MTL resonators). Even in a dense 16-channel mixed array, the inter-element isolation among all elements was better than −14 dB.
Conclusion:
This study reveals, analyzes, and validates a novel finding that the popular dipole antennas and MTL resonators used in ultrahigh field MRI have naturally low coupling.
Significance:
These findings will simplify the construction of high-density arrays, enable new applications, and benefit imaging performance in ultrahigh field MRI.