Low-complexity decoupling of multi-frequency arrays for magnetic resonance imaging and spectroscopy using operational amplifiers

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PROJECT SUMMARY/ABSTRACT The broad objective of this proposal is to develop a new approach to the design of array coils for multi- nuclear imaging and spectroscopy. The approach will avoid the use of resonant circuits for impedance matching and for providing ‘preamplifier decoupling’ using specialized low-impedance preamplfiiers. Instead, the proposal uses high-impedance, low-noise, operational amplifiers to operate series tuned coils at multiple frequencies. Only one capacitive element is envisioned on each coil, which is relatively non- specific, but will compensate for the reactance of the coil. Standard techniques can enable that one circuit element to compensate at multiple frequencies, enabling one array coil element to be used at multiple frequencies. The motivation for this project, broadly speaking, is the rapidly increasing utilization of MRI and MRS of nuclei other than hydrogen. In virtually every case of non-1H acquisitions, it is desirable to also be able to image hydrogen, and often in simultaneous or interleaved fashion. Simultaneous multi-nuclear MRI and MRS has been suggested since the earliest days of the field, and is recently reemerging due to the development of hyperpolarized MR, high-field magnets, and the increasing availability of multi-channel broadband receivers. Hyperpolarized MRI is enabling spectroscopic imaging of other nuclei, in turn providing a wealth of emerging opportunities to characterize in vivo metabolic events. However, the short lifetime of the polarization is driving the need for array coils to provide imaging acceleration. Multi- frequency array coils are extremely complex using current technology. The approach presented here will lower the cost and complexity of array coil design, removing an entry barrier to research in multi-nuclear MRI and MRS. The specific goal of this project is to investigate and optimize the interface of RF coil arrays to low-noise preamps to implement this new multi-frequency array design method. Three aims are defined; first to evaluate the noise figure of each of several interface approach, second to assess the decoupling provided by the best approaches from aim 1, and then third to compare coil arrays built using conventional approaches to a multi-frequency array built using the best performing approach from aims 1 and 2. All design procedures will be built into MATLAB scripts and made publicly available, along with all specifics of the test arrays used in this project to assist other researchers to design multi-frequency arrays.