The advancement of clinical applications of ultrahigh field (UHF) MRI depends heavily on advances in technology, including the development of new radiofrequency (RF) coil designs. Currently, the number of commercially available 7 T head RF coils is rather limited, implying a need to develop novel RF head coil designs that offer superior transmit and receive performance. RF coils to be used for clinical applications must be robust and reliable. In particular, for transmit arrays, if a transmit channel fails the local specific absorption rate may increase, significantly increasing local tissue heating. Recently, dipole antennas have been proposed and used to design UHF head transmit and receive arrays. The dipole provides a unique simplicity while offering comparable transmit efficiency and signal-to-noise ratio with the conventional loop design. Recently, we developed a novel array design in our laboratory using a folded-end dipole antenna. In this work, we developed, constructed and evaluated an eight-element transceiver bent folded-end dipole array for human head imaging at 7 T. Driven in the quadrature circularly polarized mode, the array demonstrated more than 20% higher transmit efficiency and significantly better whole-brain coverage than that provided by a widely used commercial array. In addition, we evaluated passive dipole antennas for decoupling the proposed array. We demonstrated that in contrast to the common unfolded dipole array, the passive dipoles moved away from the sample not only minimize coupling between the adjacent folded-end active dipoles but also produce practically no destructive interference with the quadrature mode of the array.

Purpose To explore the potential of deuterium metabolic imaging (DMI) in the human brain in vivo at 7 T, using a multi‐element deuterium (2H) RF coil for 3D volume coverage. Methods 1H‐MR images and localized 2H MR spectra were acquired in vivo in the human brain of 3 healthy subjects to generate DMI maps of 2H‐labeled water, glucose, and glutamate/glutamine (Glx). In addition, non‐localized 2H‐MR spectra were acquired both in vivo and in vitro to determine T1 and T2 relaxation times of deuterated metabolites at 7 T. The performance of the 2H coil was assessed through numeric simulations and experimentally acquired B1+ maps. Results 3D DMI maps covering the entire human brain in vivo were obtained from well‐resolved deuterated (2H) metabolite resonances of water, glucose, and Glx. The T1 and T2 relaxation times were consistent with those reported at adjacent field strengths. Experimental B1+ maps were in good agreement with simulations, indicating efficient and homogeneous B1+ transmission and low RF power deposition for 2H, consistent with a similar array coil design reported at 9.4 T. Conclusion Here, we have demonstrated the successful implementation of 3D DMI in the human brain in vivo at 7 T. The spatial and temporal nominal resolutions achieved at 7 T (i.e., 2.7 mL in 28 min, respectively) were close to those achieved at 9.4 T and greatly outperformed DMI at lower magnetic fields. DMI at 7 T and beyond has clear potential in applications dealing with small brain lesions.

Purpose To improve whole‐brain SNR at 7 Tesla, a novel 32‐element hybrid human head array coil was developed, constructed, and tested. Methods Our general design strategy is based on 2 major ideas: Firstly, following suggestions of previous works based on the ultimate intrinsic SNR theory, we combined loops and dipoles for improvement of SNR near the head center. Secondly, we minimized the total number of array elements by using a hybrid combination of transceive (TxRx) and receive (Rx) elements. The new hybrid array consisted of 8 folded‐end TxRx‐dipole antennas and 3 rows of 24 Rx‐loops all placed in a single layer on the surface of a tight‐fit helmet. Results The developed array significantly improved SNR in vivo both near the center (∼20%) and at the periphery (∼20% to 80%) in comparison to a common commercial array coil with 8 transmit (Tx) and 32 Rx‐elements. Whereas 24 loops alone delivered central SNR very similar to that of the commercial coil, the addition of complementary dipole structures provided further improvement. The new array also provided ∼15% higher Tx efficiency and better longitudinal coverage than that of the commercial array. Conclusion The developed array coil demonstrated advantages in combining complementary TxRx and Rx resonant structures, that is, TxRx‐dipoles and Rx‐loops all placed in a single layer at the same distance to the head. This strategy improved both SNR and Tx‐performance, as well as simplified the total head coil design, making it more robust.