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Nikolai I Avdievich¹, Anton V Nikulin^1,2, Dario Bosch^1,2, Georgiy Solomakha¹, and Klaus Scheffler^1,2
1High-Field MR Center, Max Planck Institute for Biological Cybernetics, Tübingen, Germany, ²Biomedical Magnetic Resonance, University of Tübingen, Tübingen, Germany

Keywords: High-Field MRI, RF Arrays & Systems, Dipole antenna

Homogeneity and coverage of transmit (Tx) RF  coils at ultra-high field (UHF,>7 T) can be improved by 3D RF shimming. This, however, requires using multi-row Tx-arrays. Dipole antennas provide unique simplicity and robustness while offering comparable Tx-efficiency and SNR to conventional loop designs. Single-row UHF dipole Tx-arrays for human head imaging have been previously described. Recently, we developed a novel type of dipole elements, a folded-end dipole, which improved the longitudinal coverage and specific absorption rate (SAR) efficiency. In this work, we developed, constructed, and evaluated a 16-element double-row transceiver folded-end dipole array for human whole-brain imaging at 9.4 T.

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Soo Han Soon^1,2, Matt Waks¹, Hannes M. Wiesner¹, Xiao-Hong Zhu¹, Michael T. Lanagan³, Qing X. Yang⁴, and Wei Chen^1,2
1Center of Magnetic Resonance Research (CMRR), Department of Radiology, University of Minnesota, Minneapolis, MN, United States, ²Department of Biomedical Engineering, University of Minnesota, Minneapolis, MN, United States, ³Department of Engineering Science and Mechanics, Pennsylvania State University, University Park, PA, United States, ⁴Center for NMR Research, Department of Neurosurgery and Radiology, College of Medicine, Pennsylvania State University, Hershey, PA, United States

Keywords: High-Field MRI, New Devices, High Permittivity Material (HPM), High Dielectric Constant (HDC) Material

Novel methods such as high-permittivity materials (HPM) and metasurfaces have improved RF coil transmission efficiency and receive field (B₁^-) sensitivity for MRI applications at ultrahigh field. One of the recent studies, which applied ceramic HPM helmet with the permittivity of 100, showed significant improvement in signal-to-noise ratio (SNR). Motivated from the previous studies with various forms of HPM at 3T and 7T, this study introduces an easy and accessible method with an HPM slurry helmet to largely improve imaging quality of human brain MRI at 7T, which could improve B₁^- field by 57% and SNR by 47%.

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Bei Zhang¹, Daniel Lowrance¹, and Anke Henning^1
1Advanced Imaging Research Center, UTSouthwestern Medical Center, Dallas, TX, United States

Keywords: High-Field MRI, Head & Neck/ENT

In this work, we represented 7T simultaneous brain and cervical spinal cord images with diagnostic quality. The images were acquired with a 16-channel transceiver array in a 7T 8-channel parallel transmit system which has RF shimming capability, Specifically, we acquired MP2RAGE and FLAIR images of the head and T2-weighted and GRE images of the cervical spinal cord with parameter settings in sequences for clinical applications in our center. These images show high-resolution anatomical structures and nice contrast of white and gray matters. Moreover, all these images were acquired without changing the table position or repositioning the volunteers during the scan.

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Junghwan Kim^1,2, Changyu Sun^1,3, Chan-Hong Moon⁴, Hoby Hetherington^1,5, and Jullie Pan^1
1Radiology, University of Missouri, Columbia, MO, United States, ²EECS, University of Missouri, Columbia, MO, United States, ³BBCE, University of Missouri, Columbia, MO, United States, ⁴Radiology, University of Pittsburgh, Pittsburgh, PA, United States, ⁵Resonance Research Inc., Billerica, MA, United States

Keywords: High-Field MRI, RF Arrays & Systems, Rx array

While the Tx performance of the 8x2 transceiver has been shown to achieve excellent amplitude and homogeneity, with its limited coil numbers (16), it is thought to give substantially lower SNR and acceleration in comparison to conventional arrays (8Tx/32Rx). It is recognized however, that the Tx decoupling is also constructive for Rx since the SNR and g-factors benefit from the decreased noise correlation. We evaluated the SNR, g factors, and noise covariance and found that up to an in-plane acceleration value of approximately <=4, the transceiver gives comparable performance to a commercial reference coil.

Akbar Alipour¹, Gaurav Verma¹, Andrew Frankini¹, Bradley N Delman¹, and Priti Balchandani^1
1Radiology, Icahn School of Medicine at Mount Sinai, New York, NY, United States

Keywords: High-Field MRI, Spectroscopy

Magnetic resonance spectroscopy (MRS) can particularly benefit from substantial enhancement in SNR and spectral resolution at ultra-high field (UHF ≥7T), enabling improved quantification of metabolites. However, at 7T wavelength effects cause a highly inhomogeneous transmit magnetic field in the human brain, with lower transmit efficiency in the posterior-fossa manifesting as signal dropout in this region. Recently, we reported advantages of a surface-applied inductively-coupled radiofrequency array to improve transmit efficiency and signal sensitivity at 7T MRI focusing on cerebellum and inferior temporal lobes. Here we demonstrate the feasibility and effectiveness of in-vivo MRS using the array in human cerebellum at 7T.

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Eberhard Daniel Pracht¹, Daniel Löwen¹, Laurent Lamalle², Franck Mauconduit³, Vincent Gras³, Nicolas Boulant³, and Tony Stöcker^1,4
1German Center for Neurodegenerative Diseases (DZNE), Bonn, Germany, ²GIGA-CRC in Vivo Imaging, University of Liège, Liège, Belgium, ³Université Paris-Saclay, Commissariat à l’Energie Atomique, CNRS, NeuroSpin, BAOBAB, Paris-Saclay, France, ⁴Department of Physics and Astronomy, University of Bonn, Bonn, Germany

Keywords: High-Field MRI, Brain

We present single channel universal GRAPE pulses for optimized T₁ and T₂ weighted (fluid suppressed) imaging on clinical ultra-high field systems. B₀ and B₁ inhomogeneities are effectively mitigated while no pulse calculations are necessary during the imaging session. Compared to a parallel transmission set-up SAR estimation is less complex, and with more established history of safe use, it makes this approach a promising tool for clinical applications such as lesion detection. 

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I T Maatman¹, S Ypma¹, K T Block², M C Maas¹, J Schulz¹, and T W J Scheenen^1
1Department of Medical Imaging, Radboud University Medical Center, Nijmegen, Netherlands, ²Department of Radiology, NYU Langone Health, New York, NY, United States

Keywords: High-Field MRI, Body, Radial MRI

Abdominal MRI at 7T  is sensitive to transmit field inhomogeneities and motion-induced artifacts. Transmit inhomogeneities have previously been addressed using time-interleaved acquistion of modes (TIAMO), providing uniform flip angles across a large field-of-view in the body. Meanwhile, the radial stack-of-stars sequence has been shown to be well-suited for motion-corrected MRI. In this work, TIAMO and motion-corrected radial MRI were combined to create abdominal images of three volunteers at high spatial resolutions. Results showed homogeneous transmit fields in all volunteers with excellent image quality at very high resolution. However, low-resolution scans suffered from artifacts due to gradient non-linearities and residual motion.

Johannes Anton Grimm^1,2, Christoph Stefan Aigner³, Sebastian Dietrich³, Stephan Orzada¹, Thomas M. Fiedler¹, Armin M. Nagel^1,4, Mark E. Ladd^1,2,5, and Sebastian Schmitter^1,3,6
1Medical Physics in Radiology, German Cancer Research Center (DKFZ), Heidelberg, Germany, ²Faculty of Physics and Astronomy, Heidelberg University, Heidelberg, Germany, ³Physikalisch-Technische Bundesanstalt (PTB), Braunschweig and Berlin, Germany, ⁴Institute of Radiology, University Hospital Erlangen, Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU), Erlangen-Nürnberg, Germany, ⁵Faculty of Medicine, Heidelberg University, Heidelberg, Germany, ⁶Center for Magnetic Resonance Research, University of Minnesota, Minneapolis, MN, United States

Keywords: High-Field MRI, Liver

Using a 32-Tx-channel whole-body RF antenna array at 7T could benefit exciting large body parts as these regions often suffer from flip angle inhomogeneity or dropouts. This study compares static pTx and 3D pTx pulses with a varying number of kT-points to the CP+ mode and non-optimized shim. With static pTx, the flip angle dropouts are reduced, and 2-3 kT-points seemed to deliver the best tradeoff between flip angle homogeneity and RF power.

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Max Lutz¹, Christoph Stefan Aigner¹, Sebastian Flassbeck^2,3, Felix Krüger¹, Constance G. F. Gatefait¹, Tobias Schaeffter^1,4,5, and Sebastian Schmitter^1,6,7
1Physikalisch-Technische Bundesanstalt, Braunschweig and Berlin, Germany, ²Dept. of Radiology, Center for Biomedical Imaging, New York, NY, United States, ³Center for Advanced Imaging Innovation and Research, New York, NY, United States, ⁴School of Biomedical Engineering and Imaging Sciences, King's College London, London, United Kingdom, ⁵Department of Biomedical Engineering, Technical University of Berlin, Berlin, Germany, ⁶Medical Physics in Radiology, German Cancer Research Center (DKFZ), Heidelberg, Germany, ⁷Center for Magnetic Resonance Research, University of Minnesota, Minneapolis, MN, United States

Keywords: High-Field MRI, High-Field MRI

For pTx applications, knowledge of the underlying Tx channel-wise B₁⁺ profile is essential. In this work, we present a hybrid absolute B₁⁺-mapping approach where MRF-based B₁⁺-mapping  is utilized to map the channel-wise absolute B₁⁺ profile, providing higher accuracy at low flip angles than standard methods. The hybrid approach is compared to mapping each Tx channel separately using the MRF-based method. Phantom and body in-vivo measurements at 7T show good agreement between the two approaches.

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Keywords: MR Fingerprinting/Synthetic MR, Brain

3D MRF with spiral projection trajectory was implemented on the 7T NexGen scanner to take advantage of its SNR benefit and state-of-the-art gradient system. To achieve high-fidelity and high-efficiency multi-parameter mapping at the mesoscale, novel techniques were developed to overcome several technical challenges in performing this acquisition, including spiral residual gradient compensation, trajectory measurement, water-only excitation RF pulse, B₀ correction, B₁⁺ correction and frequency response correction. The proposed technical developments enabled high-quality whole-brain T₁, T₂, and proton density mapping at 1-mm isotropic resolution in 1 minute, and 560mm isotropic resolution in 4-minutes scan time.

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Keywords: High-Field MRI, Data Acquisition, Brain imaging

Interest in pursuing MRI at ultra-high field (UHF) is increasing owing to increased SNR. However, MRI at UHF presents acquisition challenges due to decreased T2* and worsened field inhomogeneities. Rapid sampling strategies such as spiral and echo planar (EPI) acquisitions have been proposed to help mitigate these challenges. Incorporation of field monitoring to UHF applications has been demonstrated to improve the reconstruction of these images thanks to direct measurement and correction of spatiotemporal phase accrual. Here we demonstrate field-monitoring-enabled spiral and EPI acquisitions using Pulseq and field cameras.

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Gabriele Bonanno^1,2,3, Tom Hilbert^4,5,6, Patrick Liebig⁷, José P. Marques⁸, and Tobias Kober^4,5,6
1Advanced Clinical Imaging Technology, Siemens Healthineers International AG, Bern, Switzerland, ²Magnetic Resonance Methodology, Institute of Diagnostic and Interventional Neuroradiology, University of Bern, Bern, Switzerland, ³Translational Imaging Center (TIC), Swiss Institute for Translational and Entrepreneurial Medicine, Bern, Switzerland, ⁴Advanced Clinical Imaging Technology, Siemens Healthineers International AG, Lausanne, Switzerland, ⁵Department of Radiology, Lausanne University Hospital and University of Lausanne, Lausanne, Switzerland, ⁶LTS5, École Polytechnique Fédérale de Lausanne (EPFL), Lausanne, Switzerland, ⁷Magnetic Resonance, Siemens Healthcare GmbH, Erlangen, Germany, ⁸Donders Institute for Brain Cognition and Behaviour, Radboud University, Nijmegen, Netherlands

Keywords: High-Field MRI, RF Pulse Design & Fields, B1+ mapping

To fully exploit the strengths of UHF imaging, accurate B₁⁺ mapping is essential, ideally in 3D with sufficient coverage and high dynamic range. However, resulting scan times on the order of minutes are problematic, especially with the prospect of increased clinical use of 7T imaging. We implemented a compressed sensing readout and reconstruction for the SA2RAGE technique yielding <30 s scan time for a whole-brain, 4-mm isotropic resolution B₁⁺ map. We tested different acceleration factors, validated against the GRAPPA-accelerated reference protocol of ~2 min and found <0.05 relative B₁⁺ difference in most regions of the brain.

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Keywords: High-Field MRI, Quantitative Susceptibility mapping

This work presents the first QSM images obtained on the 11.7T whole body Iseult system, using tailored parallel transmission k_T-point pulses and a virtual coil approach for coil combination, on a post mortem brain.

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Ayhan Gursan¹, Mark Gosselink¹, Dimitri Welting¹, Martijn Froeling¹, Hans Hoogduin¹, Evita Wiegers¹, Dennis W.J. Klomp¹, and Jeanine J. Prompers^1
1Center for Image Sciences, University Medical Center Utrecht, Utrecht, Netherlands

Keywords: Whole Body, Metabolism, Deuterium, Phosphorus

Deuterium (²H) and phosphorus (³¹P) MRS are complementary methods for evaluating tissue metabolism non-invasively in vivo. Combined ²H and ³¹P MRS would therefore be of interest for various applications. In this work, we developed a double tuned ²H/³¹P whole-body birdcage transmit coil for 7T, for ²H and ³¹P MRS with homogeneous excitation over a large field-of-view. The B₁⁺ variation of the whole-body birdcage coil over a body-sized phantom was 14% for ²H and 25% for ³¹P. Using a two-channel ²H/³¹P prototype receive array, we obtained high-quality ²H and ³¹P 3D MRSI data in the brain, liver, and lower-leg muscles.

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Johnny Chris Der Hovagimian^1,2, Pedram Yazdanbakhsh^2,3, Marcus Couch^2,3,4, and David A. Rudko^1,2,3
1Department of Biomedical Engineering, McGill University, Montreal, QC, Canada, ²McConnell Brain Imaging Centre, Montreal Neurological Institute and Hospital, Montreal, QC, Canada, ³Department of Neurology and Neurosurgery, McGill University, Montreal, QC, Canada, ⁴Siemens Healthcare Limited, Montreal, QC, Canada

Keywords: High-Field MRI, RF Arrays & Systems

An optimized RF coil was constructed for 7T, Phosphorus (³¹P) Magnetic Resonance Spectroscopic Imaging (MRSI) of the whole brain including the cerebellum. The cerebellum is a region not well covered by most existing ³¹P coils. The design consisted of an optimized 16-rung high-pass birdcage transmit coil and a 24-channel phased array receive coil affixed to a custom head-shaped former. The coil provided high sensitivity to ³¹P signals across the whole brain and brainstem. In vivo ³¹P 3D CSI experiments showed high quality spectra with regional PCr SNR values near the cerebellum comparable to values near the brain centre.