Circuit design for broadband decoupling in multi-coil multi-nuclear applications

Abstract

The wealth of information available from multinuclear magnetic resonance imaging and spectroscopy is largely untapped in the clinical setting. This is due to a multitude of challenges in the pipeline ranging from acquisition strategies, hardware design, processing, and interpretation/analysis. As a small part of addressing these challenges, this work presents a straightforward approach for broadband decoupling between coils. This circuit was created with the implementation of a series PIN diode and was evaluated on the bench and experimentally for ¹H, ³¹P and ²³Na at 3 T. Individual coils were single-tuned with this decoupling network and stacked to enable a switched triple-tuned coil. These coils were evaluated in various purposefully coupled configurations and compared to a narrowband trap active detuning network to demonstrate potential modularity of this design. Narrowband trapped coils showed drops in SNR when combined with other coils, presumably due to coupling between receiver elements tuned to different frequencies. This broadband decoupling behavior was shown to be independent of positioning through coils oriented to be nearly perfectly geometrically coupled and the addition of a three-element array of the same size. This configuration was validated on a post-mortem pig to verify the losses of the network did not prohibit its use for preclinical imaging and spectroscopy applications. Although losses were incurred as a result of the broadband decoupling network, it enabled a modular design that can be adapted to a given study without significant compromise of the signal integrity and could eliminate the need for certain custom coils for multi-nuclear studies.