Rolf Pohmann¹, Nikolai Avdievitch¹, and Klaus Scheffler^1,2
1Magnetic Resonance Center, Max Planck Institute for Biological Cybernetics, Tübingen, Germany, ²Biomedical Magnetic Resonance, University of Tübingen, Tübingen, Germany

The increase in SNR with higher field strength is one of the main drivers for ultra high field MRI. Here, the sensitivity gain is determined for phantoms in five different fields between 3 T and 14.1 T, using identical small surface coils and correcting for all scanner specific influences. A strong, more than quadratic SNR gain with increasing field strength was found, which applies to many animal studies and to measurements with weakly loading samples.

Sarah M Jacobs¹, Jeanine J Prompers¹, Wybe JM van der Kemp¹, Tijl A van der Velden¹, Mark WJM Gosselink¹, Ettore F Meliadò¹, Hans M Hoogduin¹, Graeme F Mason², Robin A de Graaf^2,3, Anja G van der Kolk^1,4, Cezar Alborahal¹, Dennis W Klomp¹, and Evita C Wiegers^1
1Department of Radiology and Nuclear Medicine, University Medical Center Utrecht, Utrecht, Netherlands, ²Department of Radiology and Biomedical Imaging, Magnetic Resonance Research Center, Yale University School of Medicine, New Haven, CT, United States, ³Department of Biomedical Engineering, Yale University School of Medicine, New Haven, CT, United States, ⁴Department of Radiology, Radboud University Medical Center, Nijmegen, Netherlands

We have shown that it is feasible to perform POCE MRS in the human brain at 7T during a uniformly labeled [U-¹³C] glucose infusion in three healthy volunteers, using a ¹³C birdcage head coil combined with 8 transmit-receive ¹H antennas with a 32-channel ¹H receive array. STEAM-POCE and sLASER-POCE provided similar sensitivity for the [4-¹³C]-Glx-H4 signals. POCE examinations could be performed in two locations, i.e. the frontal and occipital lobe, in one session, allowing them to be easily merged with ¹H MRI.

Paul-François Gapais^1,2, Michel Luong³, Saadou Almokdad², Elodie Georget¹, and Alexis Amadon^2
1Multiwave Imaging SAS, Marseille, France, ²Université Paris-Saclay, CEA, CNRS, BAOBAB, NeuroSpin, Gif-sur-Yvette, France, ³Université Paris-Saclay, CEA, IRFU, DACM, Gif-sur-Yvette, France

The noise covariance matrix is useful for SNR and g-map computation and, with the noise correlation matrix, commonly taken as metrics to characterize decoupling of denser and denser receive arrays. Roemer provided a resistance matrix accounting for noise correlation. In the literature, Bosma defined the noise covariance matrix from the scattering matrix, easing predictions based on electromagnetic simulations or VNA measurements. Here noise correlation is analyzed for 50 Ω power-matched and low-input impedance preamplifiers. As predicted by Bosma, strong coupling does not necessarily imply a high noise correlation, which also depends on the ports impedance matching. 

Giovanni Costa¹, Sadri Güler^2,3, Peter Baltus¹, Maarten Paulides¹, and Irena Zivkovic^1
1Department of Electrical Engineering, Technology University of Eindhoven, Eindhoven, Netherlands, ²Department of Electrical Engineering, Technical University of Denmark, Kongens Lyngby, Denmark, ³Danish Research Centre for Magnetic Resonance, Centre for Functional and Diagnostic Imaging and Research, Copenhagen University Hospital Amager and Hvidovre, Copenhagen, Denmark

One of the major challenges in the design of multichannel arrays for UHF MRI is minimizing coupling between elements. Shielded-coaxial-cable (SCC) coils have been recently proposed as highly decoupled elements per se: however, the decoupling mechanism of SCC coils is still not determined. In this work, we examined the relationship between coupling, surface current density uniformity, and the total current on coil conductor through measuring and simulating three different 2-coils arrays. While no correlation was observed between surface current density uniformity and interelement coupling, a negative correlation was observed between the coupling and the total current on coil conductor.

Joseph Busher¹, Edith Valle², Steven M. Wright^1,2, and Mary P. McDougall^1,3
1Biomedical Engineering, Texas A&M, College Station, TX, United States, ²Electrical and Computer Engineering, Texas A&M, College Station, TX, United States, ³Electrical and Computer Engineering, Texas A&M, C, TX, United States

The use of traps as well as the use of switching circuitry to develop multinuclear coils is well established. However, it is well known that the use of traps introduces undesired losses to one or more nuclei in the structure while switching eliminates applications requiring true simultaneous imaging. As a result, our group developed a triple-tuned volume coil that solely uses geometric decoupling using only two structures. The coil demonstrated homogeneous fields with sufficient decoupling between the structures to acquire multinuclear NMR data. 

Jérémie Clément¹ and Özlem Ipek^1
1Biomedical Engineering Department, School of Biomedical Engineering and Imaging Sciences, King's College London, London, United Kingdom

A method for validation of the simulation model with respect to experimental  results is introduced for an 8-channel parallel-transmit dipole coil array. An original approach to include RF losses is described. The simulation results were quantitatively compared to the experimental data in terms of scattering parameters, individual transmit field (magnitude/phase) and combined transmit field. Two distinct configurations, not including RF losses were compared to the proposed approach. High correlation was achieved between simulated and experimental data. We conclude that with the proposed approach for RF losses, a robust validation is achieved for the 8-channel parallel-transmit dipole coil array at 7T.

Tiago Martins¹ and Tamer S Ibrahim^1
1University of Pittsburgh, Pittsburgh, PA, United States

In this work, we explain the tuning procedure for a new conforming Tic-Tac-Toe (TTT) array and the findings that were observed during this procedure. These findings help shape how the array can be used in building a 7 Tesla RF coil system for neuroimaging applications.. It is shown that a 2-channel and 4-channel configurations can be tuned similarly and produce similar magnetic field distribution and intensities.

Soo Han Soon^1,2, Matt Waks¹, Hannes M. Wiesner¹, Xin Li¹, Xiao-Hong Zhu¹, and Wei Chen^1,2
1CMRR, Department of Radiology, University of Minnesota, Minneapolis, MN, United States, ²Department of Biomedical Engineering, University of Minnesota, Minneapolis, MN, United States

Deuterium (²H) MRS imaging (DMRSI) enables us to measure both the cerebral metabolic rate of glucose and TCA cycle rate and to image brain tumor with an excellent contrast.  It is common to apply two sets of ²H and ¹H RF coils for performing DMRSI, resulting in coil complexity and RF interference. We introduce an 8-channel ²H-¹H dual-frequency loop coil array with LC tanks, enabling each loop coil being tuned to ²H and ¹H resonant frequencies simultaneously. We have constructed a prototype head coil for human brain applications at 7 Tesla and validated the coil via benchtop and imaging tests. 

Benjamin M Hardy^1,2, Yue Zhu^1,3, Mark D Does^1,4,5, Adam W Anderson^1,3,4, and John C Gore^1,2,3,4
1Vanderbilt University Institute of Imaging Science, Vanderbilt University, Nashville, TN, United States, ²Department of Physics and Astronomy, Vanderbilt University, Nashville, TN, United States, ³Department of Radiology and Radiological Sciences, Vanderbilt University Medical Center, Nashville, TN, United States, ⁴Department of Biomedical Engineering, Vanderbilt University, Nashville, TN, United States, ⁵Department of Radiology and Radiological Science, Vanderbilt University Medical Center, Nashville, TN, United States

Magnetic Resonance Microscopy aims to produce micron scale resolution images in reasonable times, but SNR decreases as voxel sizes shrink. RF coils must be optimized and their performance depends on coil resistance and sample size. We compared the relative performance of a commercially available cryogenically cooled surface coil of 24 mm in diameter to a smaller, 1.5 mm diameter, room temperature microcoil at 15.2T. A silver microsolenoid had threefold SNR increase but with decreased FOV and susceptibility artifacts. An optimized microcoil should be able to produce images with 10 µm isotropic resolution within 10 hours with an SNR of 10. 

Andrea N Sajewski¹, Tales Santini¹, Anthony DeFranco¹, Tiago Martins¹, Jacob Berardinelli¹, Howard J Aizenstein¹, and Tamer S Ibrahim^1
1University of Pittsburgh, Pittsburgh, PA, United States

We investigated the impact of coupling (magnitude and phase) on the B₁⁺ field distribution and intensity of a 30-channel double-rowed Tic-Tac-Toe (TTT) RF array. We found that by changing the coupling of the TTT coil modules, we are able to modify the B₁⁺ distribution from a single channel and how the B₁⁺ field intensity is spread between different Z levels of the 30-channel array. This effect was seen in both simulations and experimental B₁⁺ maps.

Sadri Güler^1,2, Vitaliy Zhurbenko³, Irena Zivkovic⁴, Vincent Oltman Boer¹, and Esben Thade Petersen^1,2
1Danish Research Centre for Magnetic Resonance, Centre for Functional and Diagnostic Imaging and Research, Copenhagen University Hospital Amager and Hvidovre, Copenhagen, Denmark, ²Section for Magnetic Resonance, DTU Health Tech, Technical University of Denmark, Kgs Lyngby, Denmark, ³Department of Electrical Engineering, Technical University of Denmark, Kgs Lyngby, Denmark, ⁴Electrical Engineering Department, Technical University of Eindhoven, Eindhoven, Netherlands

The recent introduction of the flexible shielded-coaxial-cable coils (SCC) and their intrinsic high degree of decoupling between elements make them ideal for multichannel transceiver arrays needed for improved field homogeneity at ultra-high field MRI. In this work, we show the mode of operation of the SCC and that the selection of its second resonance mode is crucial to obtain its intrinsic high degree of decoupling between elements. We obtained this insight using both numerical simulations and an equivalent circuit model, which can guide to optimal SCC designs in the future.