Objective: Considering the reported elevation of ω-6/ω-3 fatty acid ratios in breast neoplasms, one particularly important application of 13C 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 13C isotope lead to detection sensitivity challenges. Previous 13C 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 13C 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 13C 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.

Purpose shimming is an important method for mitigating B1 inhomogeneity in high‐field MRI. Using independent power amplifiers for each transmit (Tx) element is the preferred method for B1 shimming but comes with a high cost. Conversely, the simplest approach to control a Tx array is by using coaxial cables of varying length in the Tx chain, but this approach is cumbersome and impractical for dynamic shimming. In this article, a system is described that enables dynamic, phase‐only, eight‐channel steering on a 7T MR scanner with only two power amplifiers.MethodsPower dividers were utilized to first split the existing two‐channel Tx signal into eight channels. Digitally controlled phase shifters on each channel were designed to provide independent phase shifts with a resolution of 22.5° (from 0°, 22.5° … 337.5°). To validate the system, an eight‐channel body dipole array was simulated and constructed for bench and 7T imaging and evaluation.ResultsThe phase conjugate steering method was employed at three different spatial positions in simulation, bench measurements, and scanner measurements—all with matching results. At the desired points, regions with homogenous were generated, indicating good Tx steering to the selected region.ConclusionThe described system can be used as a simple retrofit to existing hardware to provide phase control while avoiding the need to manually switch cables and without requiring independent power amplifiers for each channel, thus demonstrating the ability to perform dynamic shimming with increased degrees of freedom but without significantly increased hardware cost.

OBJECTIVE:Most MRI scanners are equipped to receive signals from 1H 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-1H nuclei has received less attention because of the relative lack of broadband array receivers. Non-1H 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 1H multi-channel array receivers for use with other nuclei - in this case, 13C.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-1H array to the 1H frequency for reception by the host system receiver.RESULTS:This system has been demonstrated at 4.7T and 7T while preserving SNR and isolation. 1H decoupling, particularly important for 13C detection, can be straightforwardly accommodated.CONCLUSION:Frequency translation can convert 1H-only multi-channel receivers for use with other nuclei while maintaining SNR and channel isolation while still enabling 1H decoupling.SIGNIFICANCE:This work allows existing multi-channel MRI receivers to be adapted to receive signals from nuclei other than 1H, allowing for the use of receive arrays for in vivo multi-nuclear NMR.

PurposeThis work describes the construction and evaluation of a bilateral 32‐channel receive array for breast imaging at 7T.MethodsThe receive array consisted of 32 receive coils, placed on two 3D‐printed hemispherical formers. Each side of the receive array consisted of 16 receive loops, each loop having a corresponding detachable board with match/tune capacitors, active detuning circuitry, and a balun. Coil performance was evaluated on homogeneous canola oil phantoms using a Philips Achieva 7T system. Array coil performance was compared with a bilateral forced current excitation volume coil in transmit/receive mode and with a previously reported 16‐channel unilateral coil with a similar design.ResultsThe 32‐channel array had an increase in average SNR throughout both phantoms by a factor of five as compared with the volume coil, with SNR increases up to 10 times along the periphery and three times in the center. Noise measurements showed low interelement noise correlation (average: 5.4%; maximum: 16.8%). Geometry factor maps were acquired for various acceleration factors and showed mean geometry factors <1.2, for combined acceleration factors of up to six.ConclusionsThe improvements achieved demonstrate the clear potential for use in dynamic contrast‐enhanced or diffusion‐weighted MR studies, while maintaining diagnostically relevant spatial and temporal resolutions.

Ultrahigh field imaging of the body and the spine is challenging due to the large field-of-view (FOV) required. It is especially difficult for RF transmission due to its requirement on both the length and the depth of the ${\rm{B}}_{1}^{{\rm + }}$ field. One solution is to use a long dipole to provide continuous current distribution. The drawback is the natural falloff of the ${\rm{B}}_{1}$ field toward the ends of the dipole, therefore the ${\rm{B}}_{1}^{{\rm + }}$ per unit square root of maximum specific absorption rate ${\rm{(B}}_{1}^{{\rm + }}{\rm{/ \surd SAR}}_{{\rm{max}}})$ performance is particularly poor toward the end of the dipole. In this study, a segmented element design using forced-current excitation and a switching circuit is presented. The design provides long FOV when desired and allows flexible FOV switching and power distribution without additional power amplifiers. Different element types and arrangements were explored and a segmented dipole design was chosen as the best design. The segmented dipole was implemented and tested on the bench and with a phantom on a 7T whole body scanner. The switchable mode dipole enabled a large FOV in the long mode and improved ${\rm{B}}_{1}^{{\rm + }}{\rm{/ \surd SAR}}_{{\rm{max}}}$ efficiency in a smaller FOV in the short mode.

PurposeDisorders of brain energy metabolism and neurotransmitter recycling have been implicated in multiple neurological conditions. C-13 magnetic resonance spectroscopy (C-13 MRS) during intravenous administration of C-13-labeled compounds has been used to measure turnover rates of brain metabolites. This approach, however, requires prolonged infusion inside the magnet. Proton decoupling is typically required but may be difficult to implement with standard equipment. We examined an alternative approach to monitor glucose metabolism in the human brain. Methods(13)C-enriched glucose was infused in healthy subjects outside the magnet to a steady-state level of C-13 enrichment. Subsequently, the subjects were scanned at 7T for 60min without H-1 decoupling. Metabolic modeling was used to calculate anaplerosis. ResultsBiomarkers of energy metabolism and anaplerosis were detected. The glutamate C5 doublet provided information about glucose-derived acetyl-coenzyme A flux into the tricarboxylic acid (TCA) cycle via pyruvate dehydrogenase, and the bicarbonate signal reflected overall TCA cycle activity. The glutamate C1/C5 ratio is sensitive to anaplerosis. ConclusionBrain C-13 MRS at 7T provides information about glucose oxidation and anaplerosis without the need of prolonged C-13 infusions inside the scanner and without technical challenges of H-1 decoupling, making it a feasible approach for clinical research. Magn Reson Med 78:2065-2071, 2017. (c) 2017 International Society for Magnetic Resonance in Medicine.

Performing multinuclear experiments requires one or more radiofrequency (RF) coils operating at both the proton and second-nucleus frequencies; however, inductive coupling between coils must be mitigated to retain proton sensitivity and coil tuning stability. The inclusion of trap circuits simplifies placement of multinuclear RF coils while maintaining inter-element isolation. Of the commonly investigated non-proton nuclei, perhaps the most technically demanding is carbon-13, particularly when applying a proton decoupling scheme to improve the resulting spectra. This work presents experimental data for trap circuits withstanding high-power broadband proton decoupling of carbon-13 at 7 T. The advantages and challenges of building trap circuits with various inductor and capacitor components are discussed. Multiple trap designs are evaluated on the bench and utilized on an RF coil at 7 T to detect broadband proton-decoupled carbon-13 spectra from a lipid phantom. A particular trap design, built from a coaxial stub inductor and high-voltage ceramic chip capacitors, is highlighted owing to both its performance and adaptability for planar array coil elements with diverse spatial orientations.

In high-field magnetic resonance imaging, the radio frequency wavelength within the human body is comparable to anatomical dimensions, resulting in B1 inhomogeneity and nonuniform sensitivity patterns. Thus, this relatively short wavelength presents engineering challenges for RF coil design. In this study, a bilateral breast coil for 1H imaging at 7 T was designed and constructed using forced-current excitation. By forcing equal current through the coil elements, we reduce the effects of coupling between the elements to simplify tuning and to ensure a uniform field across both breasts. To combine the benefits of the higher power efficiency of a unilateral coil with the bilateral coverage of a bilateral coil, a switching circuit was implemented to allow the coil to be reconfigured for imaging the left, right, or both breasts.

Carbon-13 magnetic resonance spectroscopy (13C MRS) offers a noninvasive method to assess glycogen levels in skeletal muscle and to identify excess glycogen accumulation in patients with glycogen storage disease (GSD). Despite the clinical potential of the method, it is currently not widely used for diagnosis or for follow-up of treatment. While it is possible to perform acceptable 13C MRS at lower fields, the low natural abundance of 13C and the inherently low signal-to-noise ratio of 13C MRS makes it desirable to utilize the advantage of increased signal strength offered by ultra-high fields for more accurate measurements. Concomitant with this advantage, however, ultra-high fields present unique technical challenges that need to be addressed when studying glycogen. In particular, the question of measurement reproducibility needs to be answered so as to give investigators insight into meaningful inter-subject glycogen differences. We measured muscle glycogen levels in vivo in the calf muscle in three patients with McArdle disease (MD), one patient with phosphofructokinase deficiency (PFKD) and four healthy controls by performing 13C MRS at 7T. Absolute quantification of the MRS signal was achieved by using a reference phantom with known concentration of metabolites. Muscle glycogen concentration was increased in GSD patients (31.5±2.9 g/kg w. w.) compared with controls (12.4±2.2 g/kg w. w.). In three GSD patients glycogen was also determined biochemically in muscle homogenates from needle biopsies and showed a similar 2.5-fold increase in muscle glycogen concentration in GSD patients compared with controls. Repeated inter-subject glycogen measurements yield a coefficient of variability of 5.18%, while repeated phantom measurements yield a lower 3.2% system variability. We conclude that noninvasive ultra-high field 13C MRS provides a valuable, highly reproducible tool for quantitative assessment of glycogen levels in health and disease.

PurposeTo demonstrate the use of forced current excitation (FCE) to create homogeneous excitation of the breast at 7 tesla, insensitive to the effects of asymmetries in the electrical environment.Materials and MethodsFCE was implemented on two breast coils: one for quadrature 1H imaging and one for proton‐decoupled 13C spectroscopy. Both were a Helmholtz‐saddle combination, with the saddle tuned to 298 MHz for imaging and 75 MHz for spectroscopy. Bench measurements were acquired to demonstrate the ability to force equal currents on elements in the presence of asymmetric loading to improve homogeneity. Modeling and temperature measurements were conducted per safety protocol. B1 mapping, imaging, and proton‐decoupled 13C spectroscopy were demonstrated in vivo.ResultsUsing FCE to ensure balanced currents on elements enabled straightforward tuning and maintaining of isolation between quadrature elements of the coil. Modeling and bench measurements confirmed homogeneity of the field, which resulted in images with excellent fat suppression and in broadband proton‐decoupled carbon‐13 spectra.ConclusionFCE is a straightforward approach to ensure equal currents on multiple coil elements and a homogeneous excitation field, insensitive to the effects of asymmetries in the electrical environment. This enabled effective breast imaging and proton‐decoupled carbon‐13 spectroscopy at 7T. J. Magn. Reson. Imaging 2014;40:1165–1173. © 2014 Wiley Periodicals, Inc.

Purpose To enable high spatial and temporal breast imaging resolution via combined use of high field MRI, array coils, and forced current excitation (FCE) multi channel transmit. Materials and Methods A unilateral 16-channel receive array insert was designed for use in a transmit volume coil optimized for quadrature operation with dual-transmit RF shimming at 7T. Signal-to-noise ratio (SNR) maps, g-factor maps, and high spatial and temporal resolution in vivo images were acquired to demonstrate the utility of the coil architecture. Results The dual-transmit FCE coil provided homogeneous excitation and the array provided an increase in average SNR of 3.3 times (max 10.8, min 1.5) compared to the volume coil in transmit/receive mode. High resolution accelerated in vivo breast imaging demonstrated the ability to achieve isotropic spatial resolution of 0.5 mm within clinically relevant 90 s scan times, as well as the ability to perform 1.0 mm isotropic resolution imaging, 7 s per dynamics, with the use of bidirectional SENSE acceleration of up to R = 9. Conclusion The FCE design of the transmit coil easily accommodates the addition of a sixteen channel array coil. The improved spatial and temporal resolution provided by the high-field array coil with FCE dual-channel transmit will ultimately be beneficial in lesion detection and characterization.

left breast in LMCC-projection (rotated in the same orientation as the axial phase image) showing micro-calcifications (arrows). B). Ultra-high isotropic resolution (0.35 mm) axial phase image of the breast, after Laplacian unwrapping and homodyne filtering showing the calcifications (arrows) C). Coronally reconstructed phase image showing the same (as the bottom arrow on B).) suspected calcification (arrow). A B

good cist conspicuity, excellent parenchymal margins, and partial fat suppression. (B) High-resolution (0.7mm isotropic) BreastVIEW is judged to have sufficient SNR for clinical diagnosis. Figure 1. BreastVIEW signal (in red) as a function of the refocusing echo train (in blue circles) A distinct plateau lasting approximately till k=0 is observed. Inset: PSF of BreastVIEW. BreastVIEW: Isotropic 3D High Resolution T2-weighted Breast Imaging at 7T Ivan E. Dimitrov, Ananth Madhuranthakam, Sergey Cheshkov, Stephen Seiler, Sally Goudreau, Joseph Rispoli, Mary Preston McDougall, Steven M. Wright, and Craig R. Malloy Philips Medical Systems, Highland Heights, OH, United States, Advanced Imaging Research Center, University of Texas Southwestern Medical Center, Dallas, TX, United States, Radiology, University of Texas Southwestern Medical Center, Dallas, TX, United States, Biomedical Engineering, Texas A&M University, College Station, TX, United States

ObjectiveEvaluate the invivo muscle glycogen content in patients with glycogen storage disease by performing noninvasive 13C NMR spectroscopy in ultra‐high fields with the advantages of improved signal‐to‐noise ratio and spectral resolution.MethodsMuscle glycogen content was measured in 3 patients with McArdle disease (MD), 1 phosphofructokinase deficient (PFKD) patient, and 4 healthy controls (C). 13C spectra were acquired on a whole‐body 7T scanner (Philips Medical) using a partial volume human calf coil operating in quadrature for 1H and 13C. The coil had a small vial of acetate fixed inside, to serve as an external reference for quantification. For absolute quantification, a 1L cylindrical phantom was prepared with 100 mM glycogen, and 40 mM creatine.ResultsMuscle glycogen concentration was increased in MD (184.7±14.9 mM) and PFKD (196.0 mM) compared with C (73.1±13.0 mM). Creatine concentration and glycogen/creatine ratio respectively were 82.2±21.9 mM and 2.3±0.6 in MD, 120.5 mM and 1.6 in PFKD, 74.5±8.3 mM and 1.0±0.3 in C. T1 values, the strongly field dependent relaxation times, were established at 7T for glycogen 3.1±1.4 s and creatine 8.8±5.7 s in MD, 0.8±0.4 s and 2.0±1.4 s in C, respectively.ConclusionsMuscle glycogen concentration was 2.5‐fold increased in patients with glycogen storage disease. Noninvasive ultra‐high filed 13C NMR spectroscopy may provide a valuable tool to study glycogen storage in progression of the pathology and efficacy of treatment.Study supported by Muscular Dystrophy Association and Giant Tiger Foundation.

Jiaming Cui, Ivan Dimitrov, Sergey Cheshkov, Mary P. McDougall, Craig Malloy, and Steven M. Wright Electrical and Computer Engineering, Texas A&M University, College Station, Texas, United States, Advanced Imaging Research Center, University of Texas Southwestern Medical Center, Dallas, Texas, United States, Philips Medical systems, Cleveland, Ohio, United States, Department of Radiology, University of Texas Southwestern Medical Center, Dallas, Texas, United States, Biomedical Engineering, Texas A&M University, College Station, Texas, United States

“A nti-Q uad” SIMPLE AND ACCURATE DETERMINATION AND VISUALIZATION OF TRUE QUADRATURE SETTNGS ON COMMERCIAL MULTIPLE CHANNEL TRANSMITTERS USING ANTI-QUAD Steven M. Wright, Ivan Dimitrov, Sergey Cheshkov, Mary P McDougall, and Craig Malloy Electrical and Computer Engineering, Texas A&M University, College Station, TX, United States, Advanced Imaging Research Center, University of Texas Southwestern Medical Center, Dallas, TX, United States, Philips Medical Systems, Cleveland, OH, United States, Biomedical Engineering, Texas A&M University, College Station, TX, United States

Figure 3. Quadrature-only-FCE (A.) vs. Multix-optimized FCE (B.) B1 maps in a human breast . ROIs shown are a subset of B1 shim and power optimization ROIs to exclude regions with insufficient SNR for B1 estimation. Integration of 2-channel Parallel Transmission with Forced Current Excitation for Improved B1 Homogeneity in Breast Imaging at 7T Sergey Cheshkov, Ivan Dimitrov, Wouter Koning, Joseph Rispoli, Mary McDougall, Steve Wright, and Craig Malloy Advanced Imaging Research Center, University of Texas Southwestern Medical Center, Dallas, TX, United States, Radiology, University of Texas Southwestern Medical Center, Dallas, TX, United States, Philips Medical Systems, Cleaveland, OH, United States, UMC Utrecht, Utrecht, CX, Netherlands, Biomedical Engineering, Texas A&M University, College Station, TX, United States, Electrical Engineering, Texas A&M University, College Station, TX, United States

Foreign accent syndrome (FAS) is a rare disorder characterized by the emergence of a perceived foreign accent following brain damage. Despite decades of study, little is known about the neural substrates involved in this disorder. In this case study, MRI images of the brain were obtained during a speech task for an American English-speaking monolingual female who presented with FAS of unknown etiology and was thought to sound ‘Swedish’ or ‘Eastern European’. On the basis of MR structural imaging, the patient was noted to have frontal lobe atrophy. An fMRI picture-naming task designed to broadly engage the speech motor network revealed predominantly left-hemisphere involvement, including activation of the (1) left superior temporal and medial frontal structures, (2) bilateral subcortical structures and thalamus, and (3) left cerebellum. The results suggest an instance of substantial brain reorganization for speech motor control.