Sanghoon Kim¹, Sai Merugumala¹, and Alexander Lin^1
1Radiology, BWH Center for Clinical Spectroscopy, Boston, MA, United States

Sodium studies have shown subtle pathophysiologic changes in tissue sodium concentrations (TSC) in the early stage of the various diseases. One of the major challenges with measuring TSC is its low SNR.  Phased array coils are used to increase sodium SNR, however, they result in an inhomogeneous receive profile that makes accurate quantitation of TSC difficult. Uniformity correction is thus required and is often done by generating a sensitivity map. A previous approach introduced the concept of utilizing a universal sensitivity map to reduce total scan time. We present an improved universal sensitivity map solution.

Jenni Schulz¹, Oliver Kraff², Harald Quick^2,3, and Tom Scheenen^1,2
1Medical Imaging, Radboud UMC, Nijmegen, Netherlands, ²Erwin L. Hahn Institute for MRI, University Duisburg-Essen, Essen, Germany, ³High-Field and Hybrid MR Imaging, University Hospital Essen, Essen, Germany

Inhomogeneities across large FOVs are problematic at ultra-high field. We propose a software-based TIAMO implementation to enable similar flip angles across the body without hardware interference on the 7T MR scanner. Using an interleaved and complementary CP+/CP2+ excitation scheme, we acquired water-selective and lipid-selective 3D GRE data at high resolution demonstrating homogeneous signal distribution across the pelvis and lower abdomen.

Franck Mauconduit¹, Aurélien Massire², Vincent Gras¹, Eberhard Pracht³, Marc Lapert², Ilana Leppert⁴, Christine Lucas Tardif⁴, Sugil Kim⁵, Kamil Uludag^6,7, Tony Stoecker³, Mathieu Naudin^8,9,10, Rémy Guillevin^8,9,10, Alexandre Vignaud¹, and Nicolas Boulant^1
1Paris-Saclay University, CEA, CNRS, BAOBAB, NeuroSpin, Gif-sur-yvette, France, ²Siemens Healthcare SAS, Saint-Denis, France, ³German Center for Neurodegenerative Diseases (DZNE), Bonn, Germany, ⁴Montreal Neurological Institute, McGill University, Montreal, QC, Canada, ⁵Siemens Healthineers Ltd, Seoul, Korea, Republic of, ⁶Techna Institute & Koerner Scientist in MR Imaging, University Health Network, Toronto, ON, Canada, ⁷Center for Neuroscience Imaging Research, Institute for Basic Science & Department of Biomedical Engineering, Sungkyunkwan University, Suwon, Korea, Republic of, ⁸CHU Poitiers, Poitiers, France, ⁹LRCOM I3M, University and University Hospital of Poitiers, Poitiers, France, ¹⁰Laboratory of Applied Mathematics, UMR CNRS 7348, University of Poitiers, Poitiers, France

Parallel transmission universal pulses (UPs) consist of pre-optimized RF pulse solutions mitigating the RF field inhomogeneity problem for a given RF coil. Optimized offline on a database of representative field maps, they are designed to be robust to intersubject variability and spare the user a cumbersome online calibration. Initially designed for the MAGNETOM 7T Classic system from Siemens Healthineers, with the RF coil being strictly identical, this abstract describes the set of transformations on the pulses necessary to meet the MAGNETOM Terra specifications as well as successful in vivo results already achieved at four Terra sites using the same UPs.

Matthijs H.S. de Buck¹, James L. Kent¹, Aaron T. Hess¹, and Peter Jezzard^1
1Wellcome Centre for Integrative Neuroimaging, FMRIB, Nuffield Department of Clinical Neurosciences, University of Oxford, Oxford, United Kingdom

DANTE-SPACE can be used for visualizing intracranial vessel walls at 7T, where the flow-sensitive signal attenuation of the DANTE preparation simultaneously suppresses signal from the internal blood and external CSF. However, the efficacy of DANTE is reduced for blood moving upstream through the neck due to limited B1⁺ coverage at 7T. Here, EPG simulations are used to estimate the effect of this limited B1⁺ coverage on the achieved contrasts. A pTx-based approach which uses separate RF shims for the DANTE-preparation and the SPACE readout to improve the attenuation of blood moving through the neck is proposed, and validated in vivo.

Yidi Lu¹, Chia-Yin Wu^1,2,3, Shota Hodono^1,2, Jin Jin^2,4, David Reutens^1,2, and Martijn A Cloos^1,2
1Centre for Advanced Imaging, The University of Queensland, Brisbane, Australia, ²ARC Training Centre for Innovation in Biomedical Imaging Technology, The University of Queensland, Brisbane, Australia, ³School of Information Technology and Electrical Engineering, The University of Queensland, Brisbane, Australia, ⁴Siemens Healthcare Pty Ltd, Brisbane, Australia

The standing wave artefact affects SNR and contrast of the images in Ultra-high field (UHF) functional magnetic resonance imaging (fMRI). One way to mitigate this effect is to use parallel transmission (pTx). In this study, we evaluate the benefits of pTx for studies that investigate large-scale brain networks involved in motor control. We show that, compared to the standard circularly polarized (CP) mode, activation patterns in the posterior lobule of the cerebellum, produced by a coordinated finger flexion-extension task in both hands, are better captured using subject-specific pTx pulses.

Belinda Ding¹, Catarina Rua^1,2, and Christopher T Rodgers^1
1Wolfson Brain Imaging Centre, University of Cambridge, Cambridge, United Kingdom, ²Invicro LLC, A Konica Minolta Company, London, United Kingdom

Most 7T MRI sites have two head coils available for neuroimaging: a single-transmit coil and one capable of parallel transmission (pTx, or 8Tx). The 8Tx coil has a circularly polarised (CP) mode, allowing it to play RF waveforms identical to its 1Tx counterpart. This study compares the performance of a 1Tx coil against an 8Tx coil from the same manufacturer for routine neuroimaging. The 8Tx coil gave better B₁⁺ profiles in posterior brain regions which translates into improvements in other imaging sequences. It also enables the inclusion of pTx-enabled sequences. However, more detailed studies are needed before pooling data.

Carina Graf¹, Belinda Ding¹, Catarina Rua^1,2, and Christopher T Rodgers^1
1Wolfson Brain Imaging Centre, University of Cambridge, Cambridge, United Kingdom, ²Invicro LLC, A Konica Minolta Company, London, United Kingdom

7T MRS offers increased SNR and peak separation. Many Siemens 7T sites have both 1Tx32Rx and 8Tx32Rx head coils. Workflow is similar when using the TrueForm/CP+ mode. We compared MP2RAGE and semiLASER ¹H-MRS in brainstem in healthy volunteers to identify a preferred coil for future studies.

Results: voxelplacement, linewidth, and concentrations were not significantly different. SNR_NAA increased 27% and CRLBs for Gln, GABA & GSH trended to be lower for the 8Tx coil.

This encourages regular use of the 8Tx32Rx coil for brainstem ¹H-MRS and facilitates method development by allowing full pTx sequences to be added on to scheduled examinations. 

Mirsad Mahmutovic¹, Sam-Luca JD Hansen¹, and Boris Keil^1
1Institute of Medical Physics and Radiation Protection, TH Mittelhessen University of Applied Science, Giessen, Germany

Numerous methods for field computations of RF coils have been developed in the past. All these methods are based on Maxwell's equations or their derived wave equation. However, these methods are difficult to implement and not very intuitively to handle. In this work, we have investigated the suitability of the time-generalized Biot-Savart-law for $$$B_1$$$, $$$B_1^+$$$ and $$$B_1^-$$$-field computations. We showed that this method can be easily implemented and that the obtained results are a good approximation when reflections are neglectable.

Natalia Gudino¹, Jacco A de Zwart², Peter Van Gelderen², Stephen J Dodd¹, Jeff H Duyn², and Joe Murphy-Boesch^2
1LFMI, NIH, Bethesda, MD, United States, ²NIH, Bethesda, MD, United States

To evaluate safety of a 500 MHz inductive birdcage resonator for human brain MRI at 11.7 T, we compared phantom SAR measurements with predictions based on simulations. On a head-shaped phantom with realistic permittivity and conductivity, good correspondence was achieved in heating distributions when irradiating the phantom with 85 W RF power. The ability to predict SAR at 500MHz with simulation is critical step towards in-vivo MRI at 11.7 T.

Agazi Samuel Tesfai¹, Johannes Fischer¹, Ali Caglar Özen¹, Sébastien Bär^1,2, Patrick Eppenberger³, Lena Öhrström³, Frank Rühli³, Ute Ludwig¹, and Michael Bock^1
1Dept.of Radiology, Medical Physics, Medical Center University of Freiburg, Faculty of Medicine, University of Freiburg, Freiburg, Germany, ²Department of Neurosurgery, Section for Neuroelectronic Systems, University Medical Center Freiburg, Freiburg, Germany, ³Institute of Evolutionary Medicine, Faculty of Medicine, University of Zurich, Zurich, Switzerland

Ancient mummified samples have ultra-short T₂* which decreases with increasing field strength. Here, image quality and T₂* relaxation times are compared for different tissues of a mummified hand between a clinical 3T and a preclinical 9.4T system using a 3D UTE sequence. Although T₂* is shorter at 9.4T, image quality was superior to 3T, justifying the benefits of ultra-high fields (UHF).