Serhat Ilbey¹, Michael Garwood², Michael Bock¹, and Ali Caglar Özen^1,3
1Dept. of Radiology, Medical Physics, Medical Center – University of Freiburg, Freiburg, Germany, ²Center for Magnetic Resonance Research and Department of Radiology, University of Minnesota, Minneapolis, MN, United States, ³German Consortium for Translational Cancer Research Partner Site Freiburg, German Cancer Research Center (DKFZ), Heidelberg, Germany

MR imaging of tissue components with extremely fast transverse relaxation times require advanced MRI techniques such as continuous SWIFT (cSWIFT), Concurrent Excitation and Acquisition (CEA), and full duplex MRI. Frequency modulated pulses are used in these methods. A steady-state signal model with transverse relaxation term was formulated and solved for an arbitrary frequency and phase modulated RF pulse. An accurate expression for the optimal flip angle was derived. The performance of the new formulation was verified by a home-made Bloch equation simulator for T₂ values between 10µs and 100ms.

Yan Tong¹, Peter Jezzard¹, Caitlin O'Brien¹, and William T Clarke^1
1Wellcome Centre for Integrative Neuroimaging, FMRIB Division, NDCN, University of Oxford, Oxford, United Kingdom

T2‐relaxation under‐spin‐tagging (TRUST) is a robust spin tagging based method to quantify oxygen extraction fraction (OEF), but it lacks spatial specificity. Recently O’Brien et al. proposed a method involving multiple saturation pulses to achieve spatial specificity. Parallel transmission (pTx) provides additional degrees of freedom for spatial localisation. A pTx RF pulse design strategy based on a shells trajectory is applied to perform regional OEF measurement at 7 T. Initial in-vivo results acquired from one healthy subject showed that spatial localisation of OEF could be achieved.

Emre Kopanoglu¹, Cem M. Deniz², and Richard G. Wise^1,3
1CUBRIC, School of Psychology, Cardiff University, Cardiff, United Kingdom, ²Department of Radiology, New York University Langone Health, New York, NY, United States, ³Institute for Advanced Biomedical Technologies, University of Chieti-Pescara, Chieti, Italy

This study investigates the effect of within-scan patient motion on local-SAR for simultaneous multi-slice (SMS) imaging at 7T. A virtual body model was simulated at 104 different positions. 1-/2-/3-spokes pulses were designed to excite a region of 60 slices covering the cerebellum and the brain, using SMS-factors of 1 through 5. Local-SAR was observed to increase by up to 2.75-fold due to patient motion. Pulses with higher SMS-factors were up to 50% less sensitive against changes in local-SAR due to patient motion, compared to SMS:1 pulses. Pulses with higher SMS-factors yielded more consistent local-SAR throughout the scan.

Christoph Stefan Aigner¹ and Sebastian Schmitter^1
1Physikalisch-Technische Bundesanstalt (PTB), Braunschweig and Berlin, Germany

We demonstrate the design of adiabatic multi-band inversion pulses with high time-bandwidth products and acceptable RF power demands. The proposed utilization of GOIA single-band pulses results in smooth slice selective gradients with highly reduced RF power and matched multi-band RF waveforms. Phantom and in vivo experiments at 3T and 7T validate the simulations and demonstrate robust inversion of multiple slices over a wide range of both B₁⁺ and B₀ values.

Christina Graf¹, Christoph Stefan Aigner², Armin Rund³, Andreas Johann Lesch¹, and Rudolf Stollberger^1
1Institute of Medical Engineering, Graz University of Technology, Graz, Austria, ²Physikalisch-Technische Bundesanstalt (PTB), Braunschweig and Berlin, Germany, ³Institute of Mathematics and Scientific Computing, University of Graz, Graz, Austria

The aim of this work is to design slice-selective inversion RF pulses that are robust among $$$B1$$$-variations while the pulse energy is reduced. For that purpose, an optimal control framework based on an ensemble formulation is introduced. The numerically optimized RF pulses showed an excellent performance compared to the target magnetization for a broad range of $$$B1$$$-scalings. Phantom measurements were performed using a 32 channel head coil for receive and a birdcage body coil for transmit and revealed excellent inversion profiles.

Jürgen Herrler¹, Patrick Liebig², Rene Gumbrecht², Manuel Schmidt¹, Michael Uder³, Andreas Maier⁴, Arnd Dörfler¹, and Armin Nagel^3,5
1Institute of Neuroradiology, University Hospital Erlangen, Erlangen, Germany, ²SIEMENS Healthineers, Erlangen, Germany, ³Institute of Radiology, University Hospital Erlangen, Erlangen, Germany, ⁴Friedrich Alexander University Erlangen Nürnberg, Erlangen, Germany, ⁵Institute of Medical Physics, Friedrich Alexander University Erlangen Nürnberg, Erlangen, Germany

To homogenize signals 7 Tesla MRI reliably and fast, a pTx pulse design process was established. Trajectory, energy regularisation parameter and universal pulse shapes were calculated by solving global optimization problems using a dataset of 12 subjects (B1+ profiles, B0, VOP). Pulse shaping is done online using the actual subject‘s data acquired during the sequence preparation phase which lasts about 90s. A fitting curve for SED is also provided which, combined with online calculated SED values, aims to use the full amount of tolerable SAR. Compared with the CP-Mode, the NRMSE could be substantially improved for all 36 volunteers.

Kai Wang¹, Xingfeng shao¹, Lirong Yan¹, Jin Jin^1,2,3, and Danny Wang^1
1Laboratory of FMRI Technology (LOFT), Mark & Mary Stevens Neuroimaging and Informatics Institute, Keck School of Medicine, University of Southern California (USC), Los Angeles, CA, United States, ²School of Information Technology and Electrical Engineering, The University of Queensland,, Brisbane, Australia, ³ARC Training Centre for Innovation in Biomedical Imaging Technology, The University of Queensland, Brisbane, Australia

The goal of this work was to optimize and evaluate four types of adiabatic pulses for pulsed ASL (PASL) at 7T including Hyperbolic Secant (HS), WURST, FOCI and trFOCI pulses using theoretical simulation, phantom and in vivo scans, and compare them with pseudo-continuous ASL (pCASL). PASL with WURST pulse outperformed PASL with HS, FOCI and trFOCI in terms of labeling efficiency and residual signal, and also showed higher labeling efficiency compared with pCASL, and thus is recommended for 7T perfusion measurement.

Jun Ma¹, Xinqiang Yan², Bernhard Gruber³, Jonathan Martin¹, Zhipeng Cao², Jason Stockmann³, Kawin Setsompop³, and William Grissom^1
1Biomedical Engineering, Vanderbilt University, Nashville, TN, United States, ²Department of Radiology and Radiological Sciences, Vanderbilt University Medical Center, Nashville, TN, United States, ³Athinoula A. Martinos Center for Biomedical Imaging, Massachusetts General Hospital, Charlestown, MA, United States

To fully utilize the potential of a new cortical imaging-optimized 7T scanner with G_max= 200 mT/m & S_max=700 T/m/s gradients, 128 Rx channels, 16 Tx channels, and an AC/DC B₀ shim array, we describe a tailored parallel transmit inner-volume-suppression (IVS) pulse design, which can enable highly accelerated functional and diffusion imaging by reducing g-factor and suppressing physiological noise from ventricle CSF. 3D IVS pulses were designed using simulated B₁⁺ maps for the scanner’s 24-element coil. Simulation results demonstrated uniform inner volume suppression for 3D and 2D imaging. A 2D in-vivo IVS pulse design experiment demonstrated IVS’s ability to reduce g-factor.

Pallavi Bohidar¹, Hongwei Sun², Jonathan C. Sharp², and Gordon E. Sarty^1
1Division of Biomedical Engineering, University of Saskatchewan, Saskatoon, SK, Canada, ²Department of Oncology, University of Alberta, Edmonton, AB, Canada

Transmit Array Spatial Encoding (TRASE) is a novel MRI technique that achieves spatial encoding by introducing phase gradients in the transmit RF magnetic field (B₁). In this study, Bloch simulations were performed to investigate and study the effects of B₁ field perturbations arising from inductive coupling among RF coils for 2D TRASE imaging. Simulations show that a flip angle contribution of ~95% or higher from the primary (driven) transmit coil is required for 2D TRASE MRI. This result is of crucial importance for designers of practical TRASE transmit array systems.

Luke Watkins¹, Alix Plumley¹, Kevin Murphy¹, and Emre Kopanoglu^1
1Cardiff University Brain Research Imaging Centre, Cardiff, United Kingdom

Within-scan patient motion hampers the performance of parallel-transmit (pTx) pulses. In this study we developed a motion-robust pTx pulse (MRP) in the small tip angle regime to improve magnitude homogeneity over a range of pitch/roll/yaw rotations from 0° to 5°. The 4-spoke MRP was compared to a 3-spoke conventionally designed pulse (CDP). The MRP produced more homogenous magnitude profiles than the CDP for all evaluated rotations (0°,1°,2°,5° around each axis). The benefit of the method was more prominent with increased rotation angles. The proposed design shows potential for excitation pulses that maintain highly homogeneous magnitude profiles during patient head motion.

Ole Geldschläger¹, Tingting Shao¹, Jürgen Herrler², Armin Nagel^3,4, and Anke Henning^1,5
1High-field Magnetic Resonance, Max-Planck-Institut for biolog. Cybernetics, Tübingen, Germany, ²Institute of Neuroradiology, University Hospital Erlangen, Erlangen, Germany, ³Institute of Radiology, University Hospital Erlangen, Erlangen, Germany, ⁴Institute of Medical Physics, Friedrich Alexander University Erlangen Nürnberg, Erlangen, Germany, ⁵Advanced Imaging Research Center, University of Texas Southwestern Medical Center, Dallas, TX, United States

This study investigates universal parallel-transmission (pTx) radio-frequency-pulses for 3-dimensional local-excitation designed on different sized databases of B₀/B₁₊-maps from human heads at 7T. Thus, it prospectively abandons the need for time-consuming subject specific B₀/B₁₊-mapping and pTx-pulse calculation during the scan session. For the proposed calculation routine, the design-database does not need to include more than five heads, to achieve a pTx-pulse that excites the same 3-dimensional local-excitation target-pattern on the tested 40 different heads. The resulting universal pulses created magnetization-profiles with (in most cases) an only marginally worse Normalized-Root-Mean-Square-Error compared to the magnetization-profiles produced by pulses tailored to individual heads.

Alix Plumley¹, Luke Watkins¹, and Emre Kopanoglu^1
1CUBRIC, School of Psychology, Cardiff University, Cardiff, United Kingdom

Parallel-transmit (pTx) pulses can help overcome B1 inhomogeneity at ultra-high field, however their performance is sensitive to geometry, orientation and composition of the coil load. Head motion in pTx effectively alters the load, damaging pulse performance and reintroducing artificial contrast to images. Here, we introduce a versatile method to reduce in-plane motion sensitivity of large tip-angle, parallel transmit pulses by designing pulses based on weighted-average B1-distributions. These include B1-distributions from multiple head positions to effectively expand the area over which the pulse can function. Error in resulting inversion profiles is reliably reduced following most in-plane translations and rotations, demonstrating motion-robustness.

Redouane Jamil¹, Vincent Gras¹, Franck Mauconduit¹, and Nicolas Boulant^1
1CEA, Université Paris-Saclay, NeuroSpin, Gif sur Yvette, France

Bipolar spokes RF pulses can be employed in parallel transmission (pTX) used to mitigate the RF field inhomogeneity problem at ultra-high field in 2D.  However, their performance can dramatically drop with delays between gradients and RF pulses. This work reports a new method for (anisotropic) gradient delay correction for multi-spoke RF pulses based on so-called gradient trim blips, applicable to tilted slice and slab excitations. This solution has been tested in Bloch simulation and validated on phantom at 7T with tilted slab-selective pulses. Experimental results obtained with the corrected pulses match the simulations incorporating no gradient delay.

Xiaoxuan He¹, Naoharu Kobayashi¹, Myung Kyun Woo¹, Edward J. Auerbach¹, Xiaoping Wu¹, and Gregory J. Metzger^1
1Center for Magnetic Resonance Research, University of Minnesota, Minneapolis, MN, United States

In this simulation study, we explored the feasibility of incorporating parallel transmission to achieve a 3D inner volume MR fingerprinting with an aim to mitigate field inhomogeneities at UHF and reduce field of view (rFOV) for high resolution acquisitions and improved parameter estimation. Our preliminary results showed uniform and consistent contrast within the rFOV. We are currently working on the implementation of the method for further experimental validations.

Dario Bosch¹, Jonas Bause¹, Philipp Ehses², Moritz Zaiss^1,3, and Klaus Scheffler^1,4
1High Field Magnetic Resonance Center, Max Planck Institute for Biological Cybernetics, Tuebingen, Germany, ²German Center for Neurodegenerative Diseases, Bonn, Germany, ³Department of Neuroradiology, University Hospital Erlangen, Erlangen, Germany, ⁴Institute for Biomedical Magnetic Resonance, University Hospital Tuebingen, Tuebingen, Germany

Robust and fast measurements of the transmit field strength is of great importance particularly in parallel transmit applications at ultra-high field. In this work, a pre-saturation TurboFLASH B₁⁺ mapping sequence was optimized for 3-dimensional single-shot acquisition with spiral-centric reordering. Improved SNR and reduced artifacts were achieved by using a variable flip-angle readout. The ability of the proposed sampling scheme to perform fast whole-brain B₁⁺ mapping with low SAR was demonstrated in phantom and in-vivo experiments at 9.4 T. The obtained B₁⁺ maps were comparable to those obtained with the conventional 2D-SatTFL approach but required significantly less scan time.

GONG JIA¹, ZHOU WENSHEN¹, YU WENWEI², and HUANG SHAO YING^1
1EPD, Singapore University of Technology, Singapore, Singapore, ²Chiba University, Chiba, Japan

We propose an encoding method which combines Transmit Array Spatial Encoding (TRASE) and spatial encoding magnetic field (SEM) to improve the image quality in a permanent-magnet-array (PMA)-based low-field portable MRI system with acceleration. TRASE is used to introduce phase shift to re-arrange the signal points in local k-spaces, to gain more information quicker to increase imaging quality and speed. A significant quality improvement can be achieved in the reconstructed images, especially in the central regions, which is shown numerically. The number of rotation angles is reduced 80% for the same image quality. The experiments are being conducted for a validation.