Simulation-Driven Triple-Tuned Array for 1H, 31P and 23Na Using Composite Right- and Left-Handed Transmission Line for Rat Brain at 9.4T MRI

The use of ultrahigh-field-strength magnetic resonance imaging (MRI), such as 9.4T, is able to acquire multi-nuclear imaging with better image quality than lower field strengths. In particular the acquisition of sodium (23Na) or phosphorus (31P) images could benefit with higher signal-to-noise ratio (SNR). The design of radiofrequency RF coils is required to achieve a uniform field and to operate at the corresponding frequency. The general method to make multiple frequency coils has the drawback of using multilayers or reducing the size of the coils, which impose restriction on the utilization of space. For the conventional multiple frequency array, the design for the coil size imposes a challenge for the optimization of SNR and field intensity. In addition, the use of multiple coils increases the coupling between each coil. To circumvent these problems, we propose the use of composite right-left handed (CRLH) transmission lines (TL), which are able to resonate to multiple frequencies. This work demonstrates a design of an array of four channels, in which each channel consists of a single CRLH element capable to resonate at three frequencies corresponding to 1H at 400 MHz, 31P at 162 MHz, and23Na at 105 MHz. The design was demonstrated with electromagnetic (EM) simulations and applied for rat brain for use in a 9.4T MRI system.