Russell Luke Lagore¹, Steen Moeller¹, Lance DelaBarre¹, Andrea Grant¹, Jerahmie Radder¹, Kamil Ugurbil¹, Essa Yacoub¹, Noam Harel¹, and Gregor Adriany^1
1Center for Magnetic Resonance Research, University of Minnesota, Minneapolis, MN, United States

In this work we developed an 8-CH dipole transceive with 24-channel loop receive array (for a total of 32 receive channels) for head imaging of anesthetized non-human primates at 10.5T. We demonstrate the benefits of receiving with both the dipole array and loop arrays to recapture SNR in deep brain structures and allow for accelerated acquisitions with near lossless parallel imaging performance up to R=3 in either AP or LR. Presented are diffusion and anatomical MR images acquired with this coil.

Myung Kyun Woo¹, Lance DelaBarre¹, Russell Lagore¹, Andrea Grant¹, Steve Jungst¹, Yigitcan Eryaman¹, Kamil Ugurbil¹, and Gregor Adriany^1
1Center for Magnetic Resonance Research, Minneapolis, MN, United States

We designed and built three elliptically arranged 8- and 16-channel transceiver dipole and loop arrays for the human head applications and evaluated the influence of coaxial feed cables on the overall array performance. The influence of coaxial feed cables was evaluated in simulation and compared against actual built arrays in terms of B1+ and SAR efficiency. For all three arrays we consistently observed ~30 % performance reduction compared to the “ideal” coil with no coaxial cables.  

Maxim Terekhov¹, Ibrahim A. Elabyad¹, Frank Resmer², Titus Lanz², Theresa Reiter^1,3, David Lohr¹, Wiebke Schlöttelburg^1,4, and Laura M. Schreiber^1
1Chair of Cellular and Molecular Imaging, Comprehensive Heart Failure Center (CHFC), University Hospital Würzburg, Wuerzburg, Germany, ²RAPID Biomedical, Rimpar, Germany, ³Department of Internal Medicine l, University Hospital Wuerzburg, Wuerzburg, Germany, ⁴Institute of Diagnostic and Interventional Radiology, University Hospital Wuerzburg, Wuerzburg, Germany

Multiple element transmits and receive (mTx) phased arrays allow for improvement of the image quality in ultra-high-field (B0≥7T) cardiac MRI (cMRI). The optimization performed for both transmit and receive requires novel approaches regarding mTx element geometry and positioning making а B1-shimming of such arrays a complicated problem. We have demonstrated the initial experience of the case-specific B1-shimming of the mTX-array design for cMRI at 7T. The design with a central symmetry of elements and tailored cost function used for driving phases optimization allows for high flexibility in shaping of predefined target B1+ profiles.

Nikolai Avdievich¹, Georgiy Solomakha², Loreen Ruhm¹, Jonas Bause^1,3, Anke Henning^1,4, and Klaus Scheffler^1,5
1Max Planck Institute for Bilogical Cybernetics, Tuebingen, Germany, ²Nanophotonics and Metamaterials, ITMO University, St.Petersburg, Russian Federation, ³Graduate School of Neural and Behavioral Sciences, Tuebingen, Germany, ⁴Advanced Imaging Research Center, University of Texas Southwestern Medical Center, Dallas, TX, United States, ⁵Department for Biomedical Magnetic Resonance, University of Tübingen, Tuebingen, Germany

We developed a novel 9.4T (400MHz) human head transceiver array consisted of 8 optimized bent folded dipole antennas. Due to an asymmetrical shape of dipoles (bending) and the RF shield, the array simultaneously excites two modes including a circular polarized mode of the array itself, and the TE mode of the human head. Mode mixing can be easily controlled by changing the folded length. As a result, the new array provides superior whole-brain coverage compared to various 8-element loop and dipole arrays or even to a more complicated 16-element loop array. In addition, the maximum local SAR is substantially reduced.

Yonghyun Ha¹, Kartiga Selvaganesan¹, Charles Rogers III¹, Baosong Wu¹, Sajad Hosseinnezhadian¹, Gigi Galiana¹, and R. Todd Constable^1
1Department of Radiology and Biomedical Imaging, Yale School of Medicine, New Haven, CT, United States

In this work, we designed a frequency division duplex RF system for frequency encoding using Bloch-Siegert shift at very low field, with a modification of dual-band pass filters. Although the off-resonance frequency (870 kHz) is very close to the Larmor frequency (1 MHz), the applied off-resonance signal can be filtered out by a modified dual-band pass filter on the receive path. This system allows us to apply a 870 kHz transmit pulse while receiving 1 MHz signal from the RF coil.

Lena Nohava^1,2, Raphaela Czerny², Michael Obermann^1,2, Jacques Felblinger³, Roberta Frass-Kriegl², Jean-Christophe Ginefri¹, and Elmar Laistler^2
1IR4M (Imagerie par Résonance Magnétique et Multi-Modalités), UMR8081, Université Paris-Sud/CNRS, Université Paris-Saclay, Orsay, France, ²Division MR Physics, Center for Medical Physics and Biomedical Engineering, Medical University of Vienna, Vienna, Austria, ³Université de Lorraine, Inserm, IADI, Nancy, France

A bench and 3 T MRI study of flexible multi-turn multi-gap coaxial coils and standard copper wire coils with 4, 7, 10 and 15 cm loop diameter is presented. The coaxial coils are made of four different cable types and can be employed for different biomedical applications where form-fitting the coil to the subject anatomy is advantageous. We evaluate the receive-only coaxial coils’ active detuning performance, their robustness upon bending and demonstrate a significant SNR gain when using bent coaxial coils instead of flat standard coils.

Natalia Gudino¹, Jacco A de Zwart¹, and Jeff H Duyn^1
1LFMI, NINDS, National Institutes of Health, Bethesda, MD, United States

We present an eight channel pTx-Rx system built with optically controlled and monitored on-coil Tx amplifiers and optical pTx control optimized for 7 T imaging. We show preliminary results of the technology implemented for human head imaging.

Bei Zhang^1,2, Gregor Adriany³, Andrea Grant³, Russell Lagore³, Brian Rutt⁴, Kamil Ugurbil³, and Riccardo Lattanzi^1,5
1Center for Advanced Imaging Innovation and Research, New York University School of Medicine, New York, NY, United States, ²Advanced Imaging Research Center, University of Texas Southwestern Medical Center, Dallas, TX, United States, ³Center for Magnetic Resonance Research, University of Minnesota, Minneapolis, MN, United States, ⁴Stanford University, Stanford, CA, United States, ⁵The Sackler Institute of Graduate Biomedical Sciences, New York University School of Medicine, New York, NY, United States

We evaluated the effect of a radio frequency shield on the signal-to-noise ratio (SNR) of a loop coil at various field strengths in simulation. At 7T, SNR constantly improves as the shield diameter increases. At higher field strengths, SNR is maximized when using an optimal shield diameter, which is inversely proportional to the frequency. We also show that central SNR for a 32-channel receive array could drop by a factor of two when using a non-optimal shield diameter at 10.5T. Inserting a transmit array between the receiver and an optimally-sized shield could considerably deteriorate SNR.

Bei Zhang^1,2, Justin Ho¹, Shota Hodono^1,3, Bili Wang¹, Ryan Brown^1,3, Riccardo Lattanzi^1,3, Markus Vester⁴, Robert Rehner⁴, and Martijn Cloos^1,3
1Center for Advanced Imaging Innovation and Research, New York University School of Medicine, New York, NY, United States, ²Advanced Imaging Research Center, University of Texas Southwestern Medical Center, Dallas, TX, United States, ³The Sackler Institute of Graduate Biomedical Sciences, New York University School of Medicine, New York, NY, United States, ⁴Siemens Healthcare, Erlangen, Germany

We constructed a 22-channel high impedance glove array for dynamic hand and wrist imaging. The glove array has a robust, flexible, comfortable, safe, and cleanable construction. Siemens Tim4G technology was used to connect coils to the scanner through a single bundled cable to streamline the workflow and permit hand postures that are uninhibited by bulky components. Compared to a rigid commercial 16-channel Hand/Wrist coil, our  22-channel glove array showed higher SNR on fingers and wrist and comparable SNR on the palm and top of the hand. Further analysis revealed low coupling between the coils that resulted in good acceleration performance.

Ksenia Lezhennikova¹, Redha Abdeddaim², Anna Hurshkainen¹, Alexandre Vignaud³, Marc Dubois^2,4, Konstantin Simovski⁵, Alexander Raaijmakers⁶, Irina Melchakova¹, Stefan Enoch², Pavel Belov¹, and Stanislav Glybovski^1
1Faculty of Physics and Engineering, ITMO University, St.Petersburg, Russian Federation, ²CNRS, Centrale Marseille, Institut Fresnel, Aix Marseille Univ, Marseille, France, ³CEA-Saclay, DRF/I2BM/Neurospin/UNIR, Université Paris-Saclay, Gif-sur-Yvette Cedex, Paris, France, ⁴CNRS, CRMBM, Aix Marseille Univ, Marseille, France, ⁵Department of Electronics and Nanoengineerin, AALTO University, AALTO, Finland, ⁶Biomedical Engineering, Eindhoven University of Technology, Eindhoven, Netherlands

We proposed a practical realization of an artificial shield for a small-animal birdcage coil for 7T MRI based on a cylindrical miniaturized corrugated structure, which demonstrates the property of a constructive interference inside the coil. The presence of a conventional metallic shield around the birdcage significantly limits the coil efficiency because of the destructive interference between the magnetic field of the shield and the primary field of the coil in the subject. We numerically and experimentally demonstrated that the proposed structure placed around the birdcage could increase the efficiency for relatively small samples due to its in-phase reflection.

Evgeniy Alekseevich Koreshin¹, Mikhail Zubkov¹, Alexander Yurievich Efimtcev², Alexandr Mikhailovich Gulko³, and Irina Valerievna Melchakova^1
1Faculty of Physics and Engineering, ITMO University, Saint-Petersburg, Russian Federation, ²Department of Radiology, Federal Almazov North‐West Medical Research Center, Saint-Petersburg, Russian Federation, ³1st urology department, City Center of Endourology and New Technologies, Saint-Petersburg, Russian Federation

We present a new design of a radiofrequency resonator for urological applications. The resonator functions by inductively coupling to the body coil of a 1.5 T MR-scanner. This configuration of the Tx-Rx path allows increasing the transmission efficiency and signal to noise ratio (SNR) while reducing the specific absorption rate (SAR). Phantom and in-vivo imaging shows that the resonator provides around 100-fold SAR reduction and 10-fold transmission efficiency increase. Phantom imaging shows doubled SNR compared to the commercial flexible 4-element Rx coil. In-vivo imaging shows only a 50% increase in SNR, improved patient positioning and reduced the artifacts rate.

Carel Costijn van Leeuwen¹, Masoud Mazraeh Mollaei Sharifian², Luca van Dijk¹, Konstantin Simovski², and Alexander J. E. Raaijmakers^1,3
1Department of radiology, University Medical Center Utrecht, Utrecht, Netherlands, ²Aalto University, Espoo, Finland, ³Biomedical Engineering, Eindhoven University of Technology, Eindhoven, Netherlands

This study compares high impedance coils to conventional loop coils for transmit purposes at 7 Tesla. A new design for high impedance coils is presented. Two eight-channel head arrays of equal dimensions were created; one using high impedance coils, one with conventional loops. B1 field maps are produced to compare transmit efficiency. Scattering parameters are measured in various loading conditions to compare inter-element coupling. The high impedance coils perform worse in terms of transmit efficiency, and better in terms of coupling.

Sheng Shen^1,2, Zheng Xu¹, Neha Koonjoo^2,3,4, and Matthew S. Rosen^2,3,4
1State Key Laboratory of Power Transmission Equipment and System Security and New Technology, Chongqing University, Chongqing, China, ²MGH/A.A. Martinos Center for Biomedical Imaging, Cambridge, MA, United States, ³Department of Physics, Harvard University, Cambridge, MA, United States, ⁴Harvard Medical School, Boston, MA, United States

The use of a close-fitting roughly head-shaped volume coil for MRI has the merit of improving the SNR from the brain. However, the surface of the RF coil follows that of the head, making it difficult to determine the optimal coil winding pattern. Here, we proposed a method which combines finite element method simulation and linear programing to optimize the coil pattern of a close-fitted RF coil with the objective of maximizing its SNR and RF-magnetic-field homogeneity for operation at ultra-low  field (6.5 mT, 276 kHz). We then tested the optimized coil  by imaging a water-filled phantom using a 3D-bSFFP.
 

Ehsan Kazemivalipour^1,2, Alireza Sadeghi-Tarakameh^1,2, Ugur Yilmaz², and Ergin Atalar^1,2
1Electrical and Electronics Engineering Department, Bilkent University, Ankara, Turkey, ²National Magnetic Resonance Research Center (UMRAM), Bilkent University, Ankara, Turkey

We propose a practical approach to designing transmit array (TxArray) precisely by integrating the equivalent circuit model of the manufactured structure and its EM simulation results to reduce the measurements and simulations differences caused by the imperfection in manufacturing. We investigate the performance of a shielded 8-channel degenerate birdcage head TxArray at 123.2MHz together with simulation and experiment to validate the proposed method. All self/mutual-inductances and self/mutual-resistances of the manufactured TxArray have been computed to determine the optimum capacitor values by minimization of the total return power from the coil.

Greig Cameron Scott¹, Shreyas Vasanawala², Fraser Robb³, and John Pauly^2
1Electrical Engineering, Stanford University, Stanford, CA, United States, ²Stanford University, Stanford, CA, United States, ³GE Healthcare, Aurora, OH, United States

We assess the use of binary phase shift keyed and amplitude shift keyed modulation to develop a very short range wireless link.  Here the signal integrity for transmission of 200 Mbps at 3.2 GHz carrier frequencies were demonstrated in a mock MRI bore environment.  This approach provides a viable path for wireless MRI receive coil data transfer.