Dennis Philipp^1,2, Endri Stoja³, Simon Konstandin¹, Robin Wilke¹, Diego Betancourt³, Thomas Bertuch³, Juergen Jenne^1,4, Reiner Umathum^1,4, and Matthias Guenther^1,2
1Fraunhofer MEVIS, Bremen, Germany, ²University of Bremen, Bremen, Germany, ³Fraunhofer FHR, Wachtberg, Germany, ⁴DKFZ, Heidelberg, Germany

A metamaterial arrangement that encloses a volume "metaBox" is shown to yield a significant and volume-homogeneous SNR enhancement in 3T MRI. Due to the integration of non-linear components, the structure self-detunes in Tx whilst being resonant in Rx. Fine-tuning capabilities are included in two different prototypes via (i) a manually trimmable capacitor and (ii) a Bluetooth-controlled digital capacitor that allows for a wireless interface. On-bench characterization as well as MRI experiments verify the functionality of the device. Thus, the metaBox is ideally suited for, e.g., imaging of extremities.

Parisa Lotfi Poshtgol¹, Soo Han Soon², Michael Lanagan³, Eugene Furman⁴, Xinlian Chen⁵, Xin Li², Xiao-Hong Zhu², Wei Chen², and Qing X Yang^1
1Center for NMR Research, Departments of Neurosurgery and Radiology, Pennsylvania State University, Hershey, PA, United States, ²Center for Magnetic Resonance Research, University of Minnesota, Minneapolis, MN, United States, ³Department of Engineering Science and Mechanics, Pennsylvania State University, State college, PA, United States, ⁴Materials Research Institute, Pennsylvania State University, State college, PA, United States, ⁵Department of Biomedical Engineering, South China University of Technology, Guangzhou, China

Helmets conformal to the human head with high or ultra-high dielectric constant (HDC/uHDC) materials have been shown to enhance the SNR of entire human head along with a receive array. However, the dielectric resonance modes (DRMs) of the helmet have not been studies systematically. This investigation aimed to; 1) describe the characteristics of the DRMs and their RF field distributions; 2) establish the relationships between DRMs and the basic geometric parameters of the helmet using numerical modeling. Understand the DRMs of large uHDC structures are fundamentally important for future applications of uHDC materials for RF field reach.

Parisa Lotfi Poshtgol¹, Navid Pourramzan Gandjii¹, Michael Lanagan², Eugene Furman³, Soo Han Soon⁴, Xinlian Chen⁵, Saber Soltani⁶, Xiao-Hong Zhu⁴, Christopher T. Sica¹, Hannes M Wiesner⁴, Wei Chen⁴, kamil Ugurbil⁴, and Qing X Yang^1
1Departments of Neurosurgery and Radiology, College of Medicine, Pennsylvania State University, Hershey, PA, United States, ²Department of Engineering Science and Mechanics, Pennsylvania State University, State college, PA, United States, ³Materials Research Institute, Pennsylvania State University, State college, PA, United States, ⁴Center for Magnetic Resonance Research, University of Minnesota, Minneapolis, MN, United States, ⁵Department of Biomedical Engineering, South China University of Technology, Guangzhou, China, ⁶Department of Electrical Engineering, The Pennsylvania State University, State college, PA, United States

Dielectric resonators with Ultra-High Dielectric Constant (uHDC) materials possess intrinsic resonance modes that have been used for RF transmission and reception.  The resonance modes and conditions of the uHDC discs were studied through computer simulations. We compared the B₁+ field and RX-sensitivity when employing cylindrical uHDC discs at both resonant and non-resonant conditions. We showed in this work, to achieve the best focusing effect into phantom, the design with uHDC material should operate around the first TE_01δ mode and lower than the second mode TE_01δ with the highest permittivity.

Akbar Alipour¹, Ameen Al Qadi¹, Gaurav Verma¹, Alan C Seifert¹, and Priti Balchandani^1
1BioMedical Engineering and Imaging Institute (BMEII), Icahn School of Medicine at Mount Sinai, Manhattan, NY, United States

Ultra-high field (UHF ≥7T) MRI scanners can provide stronger signals than standard field strengths, which boosts signal-to-noise ratio (SNR) for improved diffusion MRI (dMRI). However, at 7T, wavelength effects cause highly inhomogeneous $$$B_1^+$$$ in the human brain, with lower transmit efficiency in the cerebellum and temporal lobes manifesting as signal dropouts in these regions. Recently, we reported a simple approach of using a wireless radiofrequency (RF) array to improve transmit efficiency and signal sensitivity at 7T focusing on the posterior fossa. Here we demonstrate the feasibility and effectiveness of using the RF array for in-vivo dMRI at 7T.

Christopher T Sica¹, Parisa Lofti Poshtgol², Sebastian Rupprecht³, and Qing X Yang^2
1Radiology, Pennsylvania State University College of Medicine, Hershey, PA, United States, ²Neurosurgery, Pennsylvania State University College of Medicine, Hershey, PA, United States, ³3HyQ Research Solutions, LLC, College Station, TX, United States

Prior work has explored the use of dielectric materials to enhance imaging of the brain and spine with rectangular blocks. One area that has not been examined to date is knee imaging, where space constraints limit the use of blocks. In this work we evaluate the performance of an ultra-high dielectric constant (uHDC) curved plate (ε_r ~ 4500) for knee imaging in a clinical array at 3T. SNR gains of 9 to 71% percent were observed across the patella and patellar cartilage. Transmit efficiency increased up to 100% close to the material, with an increase in transmit inhomogeneity.

Viktor Puchnin¹, Evgeniy Koreshin¹, Anna Kalugina¹, Aleksander Efimtcev^1,2, Irina Mashchenko², Wyger Brink³, and Alena Shchelokova^1
1School of Physics and Engineering, ITMO University, Saint Petersburg, Russian Federation, ²Federal Almazov North-West Medical Research Center, Saint Petersburg, Russian Federation, ³Department of Radiology, C.J. Gorter Center for High‐Field MRI, Leiden University Medical Center, Leiden, Netherlands

Radiofrequency magnetic field homogeneity improvement and SAR reduction are two essential tasks for fetal MRI at 3T. We demonstrate for the first time that the metasurface-based pad can effectively improve the transmit efficiency while reducing SAR within the entire fetus and fetus brain. The metasurface is assembled from the metal wires loaded with capacitors. Numerical studies of a pregnant woman voxel model in the 9th month covered with the proposed metasurface centered within fetus brain (body) showed 25% (28%) transmit efficiency improvement and up to 9% (2.8%) increased magnetic field homogeneity, while the whole-body SAR was reduced by 1.2 (1.6)-fold.

Paulina Šiurytė¹, Friso de Boer¹, Can Akgun², and Sebastian Weingärtner^1
1Imaging Physics, TU Delft, Delft, Netherlands, ²Microelectronics, TU Delft, Delft, Netherlands

MRI at high and ultra high field strengths suffers from B1⁺ inhomogeneities, but B1⁺ shimming with multiple transmit coils is only available at top-line scanners. Dielectric pads allow for localized B1⁺ changes, but need to be specifically designed for the scan and anatomy. In this work we explore the use of an actively switchable dielectric device to allow for spatial B1⁺ correction without the need for multiple transmit coils.  Our phantom experiments at 3T show that coupling mini-pockets with barium titanate slurry enables various field configurations that are switchable, localized and significant in magnitude.

Seulki Yoo^1,2, Ji Seong Barg¹, Bo-yong Park^3,4, and Seung-Kyun Lee^1,2
1Department of Biomedical Engineering, Sungkyunkwan university, Suwon, Korea, Republic of, ²Intelligent Precision Healthcare Convergence, Sungkyunkwan University, Suwon, Korea, Republic of, ³Department of Data Science, Inha University, Incheon, Korea, Republic of, ⁴Center for Neuroscience Imaging Research,Institute for Basic Science, Suwon, Korea, Republic of

Ultra-high-field MRI provides improved signal-to-noise ratio (SNR) and tissue contrast. However, at the same time, it exhibits stronger RF field inhomogeneity compared to lower-field MRI. Although such inhomogeneity can be mitigated by customized RF coils and parallel transmit methodology, it is often difficult to translate these to clinical use. Recently, a simple and low-cost high dielectric-constant padding has been proposed to improve the quality of 7T brain images in many sequences. Here, we propose a novel approach to suppress the MR visibility of a water-based dielectric padding by controlled addition of iron oxide contrast agent in 7T human brain MRI. 

Léo Rémillard¹, Adam Mitchell Maunder^1,2, Ashwin Iyer¹, and Nicola De Zanche^2,3
1Electrical and Computer Engineering, University of Alberta, Edmonton, AB, Canada, ²Oncology, University of Alberta, Edmonton, AB, Canada, ³Medical Physics, Cross Cancer Institute, Edmonton, AB, Canada

Metamaterials (MTMs) have been used as passive elements to improve the receive sensitivity in MRI by enhancing the field locally, but not connected directly as receive elements. We present the design and construction of a novel 2D transmission line based MTM employed as a 4-port element combined with an additional 4-element coil array. Simulation and measurement of receive sensitivity are compared to those of a conventional 8-element coil array covering the same region. The receive sensitivity in a human torso sized phantom is found to be equivalent, while the MTM slab additionally enhances the transmit performance.

Tania del Socorro Vergara Gomez^1,2, Roxane Mamberti², Marc Dubois³, Elodie Georget³, Tryfon Antonakakis³, Alexandre Vignaud⁴, Frank Kober¹, Stefan Enoch², and Redha Abdeddaim^2
1Aix Marseille Univ, CNRS, CRMBM, Marseille, France, ²Aix Marseille Univ, CNRS, Centrale Marseille, Institut Fresnel, Marseille, France, ³Multiwave Imaging, Marseille, France, ⁴CEA, DRF/Joliot/Neurospin, Université Paris-Saclay & CNRS, Gif-sur-Yvette Cedex, France

Active and passive RF shimming approaches have been proposed to diminish the B₁⁺ inhomogeneities commonly found in a birdcage coil at 7T.  In a previous work, we have introduced a meander dipole based on two 3^rd-order Hilbert fractals as an alternative solution for passive shimming. In this work we optimized their design using six 2^nd-order Hilbert fractals. Simulations and in vivo MRI at 7T using these structures showed strong B₁⁺ enhancement in the area between the two meander dipoles whereas B₁⁺ was reduced in regions below and above the fractal pads. 

Juan Diego Sánchez Heredia¹, Wenjun Wang², Vitaliy Zhurbenko², and Jan Henrik Ardenkjær-Larsen^1
1Department of Health Technology, Technical University of Denmark - DTU, Kgs. Lyngby, Denmark, ²Department of Electrical Engineering, Technical University of Denmark - DTU, Kgs. Lyngby, Denmark

The feasibility of integrating a whole-body X-nucleus birdcage in a wide-bore clinical 3T MR scanner is evaluated. The challenge is that this extension coil has to be tightly fit into the scanner bore, having  a diameter just 16 mm smaller  than the concentric ¹H coil. Different configurations are proposed and evaluated with the purpose of minimizing interaction between the X-nucleus coil and the native ¹H body coil of the scanner. Experimental results are in agreement with simulations and demonstrate a ¹H coil detuning of 0.4 MHz due to co-integration with X-nucleus birdcage.