Laura Boehmert, Andre Kuehne, Helmar Waiczies, Daniel Wenz, Thomas Eigentler, Armin Nagel, Thoralf Niendorf

Cardiorenal syndrome (CRS) describes disorders of the heart and the kidneys in which a dysfunction of one of the organs induces a dysfunction in the other. Sodium MRI at ultrahigh magnetic fields offers an appealing strategy to gain a better functional and metabolic understanding of CRS and detect these diseases earlier. This work describes the design, construction and application of an 8-channel ¹H/²³Na RF coil tailored for cardiorenal imaging at 7.0 Tesla.

Myung Kyun Woo, Lance DelaBarre, Jingu Lee, Russell Lagore, Steve Jungst, Kamil Ugurbil, Gregor Adriany

We designed an elliptical 16-channel transceiver sleeve monopole array for human head imaging at 10.5T and evaluated the performance both in simulation and experiment.  The 16-channel sleeve monopole array was compared to 8-channel end-loaded dipole and monopole arrays. Porcine brain images acquired with the sleeve monopole array demonstrate good coverage and performance.

Nikolai Avdievich, Georgiy Solomakha, Loreen Ruhm, Klaus Scheffler, Anke Henning

Increasing the number of surface loops in a human head receive (Rx)-array improves the peripheral SNR, while the central SNR doesn’t substantially change. Recent work demonstrated that optimal central SNR at UHF requires a contribution of two current patterns associated with a combination of loops and dipoles. A novel array consisting of 8 transceiver surface loops and 8 optimized folded Rx-dipoles was developed and tested. Addition of Rx-dipoles doesn’t substantially alter B₁⁺ field and the maximum local SAR. At the same time the new design improves both central and peripheral SNR as compared to the similar 16-element array with Rx-only vertical loops.

Christian Findeklee, Oliver Lips, Peter Vernickel, Christoph Leussler, Randy Duensing

Preamplifier decoupling has been used to isolate elements of receive array coils for decades. For good SNR, decoupling of elements is essential. However, recent research results claim that this just holds for “real” electromagnetic decoupling rather than preamp decoupling as long as the SNR-optimal channel combination is used. We performed experiments on the impact of preamplifier decoupling including also accelerated imaging using SensE. We found no significant difference in SNR between preamplifier decoupled and resonant coil elements.

Bart Steensma, Ingmar Voogt, Thijs Kraaij, Peter Luijten, Martijn Cloos, Daniel Sodickson, Dennis Klomp, Cornelis van den Berg, Alexander Raaijmakers

In order to calculate ultimate intrinsic signal-to-noise ratio and specific absorption rate efficiency in the prostate, a full electromagnetic basis was calculated in the Duke human model for a prostate scan configuration. Four high-density parallel transceive arrays were simulated in the same configuration using the Finite Difference Time Domain method, and are benchmarked against the ultimate coil performance. The best performing array is a 10 dipole/20 loop array, which can achieve 73% of the ultimate intrinsic coil performance. A 32 channel RF amplifier system was installed as an add-on to our Philips 7T Achieva system, and initial experimental results using a 24 channel loop/dipole array were demonstrated. 

Lena Nohava, Raphaela Czerny, Michael Obermann, Michael Pichler, Roberta Frass-Kriegl, Jacques Felblinger, Jean-Christophe Ginefri, Elmar Laistler

The design of flexible coaxial coils (CCs) based on the single-turn single-gap concept is extended by multiple turns and multiple gaps (MTMG-CCs) to achieve a larger range of coil diameters for a given resonance frequency. An equivalent circuit for MTMG-CCs is presented and the resonance condition is solved numerically for coils with diameters up to 20 cm, 1-3 turns, and 1-3 gaps. For validation of the calculations, 27 coils with 6/9/12 cm diameters, 1-3 turns, and 1-3 gaps were built and characterized on the bench.

Jérémie Clément, Sandra Da Costa, Rolf Gruetter, Özlem Ipek

The performances of a 32-channel receive coil array combined with a tight-fitted whole-brain dipole coil array were investigated. Functional MRI data targeting the auditory cortices was acquired. Noise correlation matrices, SNR and g-factor maps were measured. Compared to a commercial 32Rx, the in-house built 8T/32Rx coil array demonstrated higher robustness in the fMRI results. Lower noise correlation coefficients were measured with the in-house built 8Tx/32Rx coil array while the overall experimentally measured SNR and g-factor maps were comparable.

Stephen Ogier, Matthew Wilcox, Sergey Cheshkov, Ivan Dimitrov, Craig Malloy, Mary McDougall, Steven Wright

A system has been developed to enable the acqusition of 16-channel ¹³C data on a Philips Achieva 7T scanner.  Radiofrequency mixers are used to convert the transmitted signal to ¹³C, and the received signal back to ¹H to be acquired by the host system's receiver.  A 16-element unilateral breast coil has been developed, and data have been acquired that show a substantial SNR improvement from use of the array. 

Junjie Ma, Ralph Hashoian, Chenhao Sun, Steve Wright, Alexander Ivanishev, Robert Lenkinski, Craig Malloy, Albert Chen, Jae Mo Park

A customized ¹H/¹³C RF head coil that consists of a ¹H quadrature transmit (Tx) and receive (Rx) coil and ¹³C quadrature transmit and array receive (QTAR) coils was developed. The performance of the new head coil was evaluated using phantoms and compared to the existing ¹³C-only quadrature Tx/Rx (QTR) head coil. Metabolic imaging of human brain was performed using the ¹H/¹³C head coil, following an injection of hyperpolarized [1-¹³C]pyruvate. 

Christopher Sica, Sebastian Rupprecht, Ryan Hou, Matthew Lanagan, Navid Gandji, Michael Lanagan, Qing Yang

We performed a human brain imaging study using a prototype conformal helmet constructed with ultrahigh dielectric constant (uHDC) materials inserted into a standard 20-Ch head coil at 3T. We characterized the transmit and receive performance of the helmet by comparing to results using the 20-Ch and 64-Ch head coil (n=5 subjects) without the uHDC helmet. The SNR and its spatial distribution within the cerebrum using the 20-Ch Coil with uHDC Helmet is comparable to that of the 64-Ch Coil. Further improvement of the uHDC helmet insert is expected to significantly improve the performance of standard receive arrays for brain imaging.

Isabelle Saniour, Gilles Authelet, Bertrand Baudouy, Rose-Marie Dubuisson, Laurène Jourdain, Georges Willoquet, Luc Darrasse, Jean-Christophe Ginefri, Marie Poirier-Quinot

We present the performance of an MR-compatible cryogenic system dedicated to cool High Temperature Superconducting (HTS) radiofrequency coils for micro-MRI at 1.5 T. A real time control and regulation of the temperature were performed to finely tune the HTS coil to the Larmor resonance frequency with a precision of 1 Hz. Firstly, we demonstrated that this cryostat does not cause any electromagnetic disturbance. Secondly, MR images of a 1 mm-cubic liquid phantom were acquired using the HTS coil as a transceiver with a spatial resolution down to (100 μm)³ under real clinical research experimental conditions.

Jan Paska, Jose Raya, Marijn Cloos

At the last years ISMRM we proposed an RF coil optimization pipeline based on a mesh structure consisting of 50-Ohm sources and copper patches. This allowed us to compute the maximal possible SNR of a given mesh as well as the emulation of concrete coil geometries in post-processing. 

In this work we present an analysis of body imaging at 7T with an appropriately chosen mesh size that can reach the UISNR. Furthermore the optimal current weights are analyzed to create a physically realizable coil that approaches the UISNR.

Shajan Gunamony, Paul McElhinney, Sarah Allwood-Spiers, Gavin Paterson, Jozien Goense

In this work, a nested array of 8-transmit elements was developed and combined with a 32-channel receive array for imaging the human brain at 7T. This setup can be used in the single channel and parallel transmit mode of the Siemens 7T scanner. The transmit array was designed to make the setup less claustrophobic and provide an open feel, benefitting fMRI and patient studies. The transmit performance of this setup is presented here.

Russell Lagore, Edward Auerbach, Naoharu Kobayashi, Steve Jungst, Steen Moeller, Greg Metzger, Kamil Ugurbil, Michael Garwood, Gregor Adriany

Sweep imaging with Fourier transformation (SWIFT) can image extremely short-lived MRI signals such as cortical bone and lung. However, it requires fast transmit/receive (T/R) switching during the gapped RF excitation, which cannot be handled with standard clinical MRI hardware. A fast transmit/receive switch (switching time ≤ 400 ns) is developed for integration into an 8-channel in-bore T/R switch interface. These T/R switches are driven via repurposed Varian PIN drivers which are, in turn, triggered via an optical-to-TTL signal. This hardware enabled the acquisition of SWIFT images of the human head at 7T with an 8-channel transmit/receive degenerate birdcage coil.

Sherry Huang, Michael Twieg, Mark Griswold

Developments in RF transmit systems have been trending towards increasing independent elements and compact designs. Previous work has shown the capability of enhancement mode Gallium Nitride (eGaN) FETs in high-efficiency switchmode RF amplifier (RFPA) based on envelope elimination and restoration (EER). Switchmode RF amplifiers, however, suffer from nonlinearity and limited dynamic range, leading to errors in excitation profiles. Here we present preliminary results on a new prototype which adds an additional modulation methods using digital controls to increase RFPA dynamic range.