The method of pole-insertion for multi-tuning cable traps was studied for multinuclear MRI and MRS applications. For many applications such as when using high-density array coils, finding a space-efficient solution to eliminate common-mode currents could be of significant benefit. This multi-tuned approach provides space efficiency at a small cost in trapping efficiency. Relative efficiency of the different cable trap modes was studied as component values were varied and at four different magnetic field strengths. In all cases, efficiencies were compared to equivalent single-tuned designs. The multi-tuned traps were able to block shield currents at multiple frequencies with only slightly degraded efficiencies as compared to their single-tuned counterparts. As in double-tuned coil design, the cable trap effectiveness at each frequency was found to be highly dependent on the trap inductor value with larger trap inductances leading to worse efficiency at the lower frequency but better efficiency at the higher frequency. This relationship held at all field strengths examined. This work presents design guidelines for the double-tuning method that are useful when designing RF coils for multinuclear studies. The design takes up less space than using two single-tuned cable traps mounted in series as is commonly done. Triple-tuned and “floating” designs were also demonstrated as proofs-of-concept for a single field strength and showed great promise to prove similarly useful in future studies.

It is now common practice to use radiofrequency (RF) array coils to increase the signal-to-noise ratio (SNR) in $^1H$ magnetic resonance imaging and spectroscopy experiments. Use of array coils for non- $^1H$ experiments, however, has been historically more limited despite the fact that these nuclei suffer inherently lower sensitivity and could benefit greatly from an increased SNR. Recent advancements in receiver technology and increased support from scanner manufacturers have now opened greater options for the use of array coils for non- $^1H$ magnetic resonance experiments. This paper reviews the research in adopting array coil technology with an emphasis on studies of the most commonly studied non- $^1H$ nuclei including $^{31}P$ , $^{13}C$ , $^{23}Na$ , and $^{19}F$ . These nuclei offer complementary information to $^1H$ imaging and spectroscopy and have proven themselves important in the study of numerous disease processes. While recent work with non- $^1H$ array coils has shown promising results, the technology is not yet widely utilized and should see substantial developments in the coming years.

Objective: Most MRI scanners are equipped to receive signals from ¹ H array coils but few support multi-channel reception for other nuclei. Using receive arrays can provide significant SNR benefits, usually exploited to enable accelerated imaging, but the extension of these arrays to non- ¹ H nuclei has received less attention because of the relative lack of broadband array receivers. Non- ¹ H nuclei often have low sensitivity and stand to benefit greatly from the increase in SNR that arrays can provide. This paper presents a cost-effective approach for adapting standard ¹ H multi-channel array receivers for use with other nuclei - in this case, ¹³ C. Methods: A frequency translation system has been developed that uses active mixers residing at the magnet bore to convert the received signal from a non- ¹ H array to the ¹ H frequency for reception by the host system receiver. Results: This system has been demonstrated at 4.7T and 7T while preserving SNR and isolation. ¹ H decoupling, particularly important for ¹³ C detection, can be straightforwardly accommodated. Conclusion: Frequency translation can convert ¹ H-only multi-channel receivers for use with other nuclei while maintaining SNR and channel isolation while still enabling ¹ H decoupling. Significance: This work allows existing multi-channel MRI receivers to be adapted to receive signals from nuclei other than ¹ H, allowing for the use of receive arrays for in vivo multi-nuclear NMR.

Objective: Considering the reported elevation of ω-6/ω-3 fatty acid ratios in breast neoplasms, one particularly important application of ¹³ C MRS could be in more fully understanding the breast lipidome's relationship to breast cancer incidence. However, the low natural abundance and gyromagnetic ratio of the ¹³ C isotope lead to detection sensitivity challenges. Previous ¹³ C MRS studies have relied on the use of small surface coils with limited field-of-view and shallow penetration depths to achieve adequate signal-to-noise ratio (SNR), and the use of receive array coils is still mostly unexplored. Methods: This work presents a unilateral breast 16-channel ¹³ C array coil and interfacing hardware designed to retain the surface sensitivity of a single small loop coil while improving penetration depth and extending the field-of-view over the entire breast at 7T. The coil was characterized through bench measurements and phantom ¹³ C spectroscopy experiments. Results: Bench measurements showed receive coil matching better than -17 dB and average preamplifier decoupling of 16.2 dB with no evident peak splitting. Phantom MRS studies show better than a three-fold increase in average SNR over the entirety of the breast region compared to volume coil reception alone as well as an ability for individual array elements to be used for coarse metabolite localization without the use of single-voxel or spectroscopic imaging methods. Conclusion: Our current study has shown the benefits of the array. Future in vivo lipidomics studies can be pursued. Significance: Development of the 16-channel breast array coil opens possibilities of in vivo lipidomics studies to elucidate the link between breast cancer incidence and lipid metabolics.

This work investigates the efficacy of “coplanar shielding,” in which copper shields are oriented concentric and coplanar to the RF coils rather than implemented as a full ground plane behind them. Following FDTD simulations to determine optimal shielding parameters, two coil geometries were constructed: a circular loop surface coil and a half-volume five-element receive array. Each was evaluated using bench measurements with and without coplanar shielding. Imaging, including accelerated SENSE imaging, was performed with the shielded and unshielded receive arrays on a whole-body 7T scanner. Results from modeled and fabricated coils showed good agreement with improvements in Q factors for all cases. Imaging showed substantial improvements in SNR and g-factors for the coplanar shielded array.