Andreas Gräßl¹, Wolfgang Renz², Fabian Hezel¹, Tobias Frauenrath¹, Harald Pfeiffer³, Werner Hoffmann³, Peter Kellman⁴, Conrad Martin¹, and Thoralf Niendorf^1,5
1Berlin Ultrahigh Field Facility, Max-Delbrueck-Center for Molecular Medicine, Berlin, Germany, ²Siemens Healthcare, Erlangen, Germany, ³Physikalisch-Technische Bundesanstalt (PTB), Berlin, Germany, ⁴Laboratory of Cardiac Energetics, National Institutes of Health/NHLBI, Bethesda, MD, United States,⁵Experimental and Clinical Research Center (ECRC), Charité Campus Buch, Humboldt-University, Berlin, Germany

Ultrahigh field cardiac MR is challenged by non-uniform B1+-distributions. A modular two-dimensional 32-channel transceiver surface coil array based on loop elements is proposed to improve parallel imaging and B1+ homogeneity for cardiac MR at 7 T. The RF characteristics were satisfying without the need for subject-specific tuning and matching. MR images were acquired showing a rather uniform intensity over the whole cardiac region and a high myocardium/blood contrast without subject-specific B1+-shimming.

Oliver Kraff^1,2, Stephan Orzada^1,2, Mohamed Choukri¹, Anja Fischer^1,2, Susanne C Ladd^1,2, Mark E Ladd^1,2, and Andreas K Bitz^1,2
1Erwin L. Hahn Institute for Magnetic Resonance Imaging, University Duisburg-Essen, Essen, Germany, ²Department of Diagnostic and Interventional Radiology and Neuroradiology, University Hospital Essen, Essen, Germany

A transmit/receive RF array was built for imaging the shoulder and upper extremities at 7 Tesla. Eight meander stripline elements were aligned on a c-shaped holder which can be split into two parts for easy patient positioning. The coil allows imaging of either the right or left upper extremity. In vivo images of the shoulder and elbow revealed uniform excitation over the whole field-of-view in both gradient and spin echo images, rendering fine anatomical details of cartilage, bone, nerves, vasculature, and tendons.

Alexander J.E. Raaijmakers¹, Maarten J. Versluis², Sebastian A. Aussenhofer², Hamza El Aidi¹, Peter Luijten¹, Tim Leiner¹, Cornelis A.T. van den Berg¹, and Andrew Webb^2
1Imaging Division, UMC Utrecht, Utrecht, Netherlands, ²J.C. Gorter Institute, LUMC, Leiden, Netherlands

Recently, a novel coil array of radiative antennas was introduced for prostate imaging. In this study, the same array is used for cardiac imaging at 7 Tesla. An additional coil array consisting of large loop coils has been constructed for comparison. Both arrays are characterized by FDTD simulations. These show that the array of radiative antennas has much higher B₁⁺ and B₁^- while the array of large loop coils has much lower SAR levels. Cine MR cardiac images have been obtained, showing higher SNR for the array of radiative antennas. With this array the right coronary artery was successfully depicted.

G Shajan¹, Jens Hoffmann¹, Klaus Scheffler^1,2, and Rolf Pohmann^1
1Max Planck Institute for Biological Cybernetics, Tuebingen, Baden Wuerttemberg, Germany, ²Department for Neuroimaging, University Hospital, Tuebingen, Germany

The well known transmit field inhomogeneity at ultra high field strengths, caused by the shorter RF wavelength in tissue, is most severe in the lower half of the brain. A dual-row 16 element transmit coil that gives the additional flexibility to shim for the lower brain was designed. Numerical investigation revealed excellent static B₁ shimming performance. In vivo shimming on a coronal slice demonstrates the ability to improve the transmit field in brain regions that are challenging to image using single-row transmit arrays. The coil can be combined with receive-only arrays for highly sensitive parallel signal reception.

Graham Charles Wiggins¹, Bei Zhang¹, Gang Chen², and Daniel Sodickson^1
1The Bernard and Irene Schwartz Center for Biomedical Imaging, NYU Medical Center, New York, NY, United States, ²The Sackler Institute of Graduate Biomedical Science, NYU School of Medicine, New York, NY, United States

While neighboring coil elements can be decoupled by various means, it is more difficult to mitigate the often substantial coupling to next nearest neighbors. This is particularly problematic with transmit arrays, since preamp decoupling cannot be used to control next nearest neighbor coupling. We present a novel array design with triangular elements which allows capacitive decoupling between neighboring coils and inductive decoupling between next nearest neighbor coils. The triangular elements also present diverse B1 profiles, allowing for acceleration along the Z direction.

Wei Zhao¹, Borjan Gagoski², Khaldoun Makhoul¹, Boris Keil¹, Azma Mareyam¹, Philipp Hoecht³, and Lawrence L Wald^1
1Athinoula A. Martinos Center for Biomedical Imaging, Dept. of Radiology Massachusetts General Hospital, Harvard Medical School, Charlestown, Massachusetts, United States, ²Electrical engineering and Computer Science, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States, ³Siemens Medical Solutions USA Inc., Charlestown, Massachusetts, United States

Parallel transmit method has provided the potential to shape excitations with practical pulse lengths and mitigate B1+ inhomogeneity and B0 inhomogeneity at high field. Increasing the number of transmit channels offers the flexibility for adjusting the phase and amplitude of each channel and the degree of the freedom for improved pulse design and SAR. In this work, we developed a 16-channel T/R degenerate birdcage head coil in a single cylindrical row, with good decoupling (>15dB) between the next neighbors and high B1+ efficiency as compared with that of an 8-channel concentrically shielded T/R array coil.

Andreas K. Bitz^1,2, Thiele Kobus³, Tom W. J. Scheenen^1,3, and Mark E. Ladd^1,2
1Erwin L. Hahn Institute for Magnetic Resonance Imaging, University Duisburg-Essen, Essen, Germany, ²Department of Diagnostic and Interventional Radiology and Neuroradiology, University Hospital Essen, Essen, Germany, ³Department of Radiology, Radboud University Nijmegen Medical Centre, Nijmegen, Netherlands

To relate information of cancer-related metabolites to anatomical location within the human prostate, a ³¹P endorectal coil (ERC) was combined with an 8-channel ¹H body array. For compliance testing, RF coupling between both coils was investigated. The compliance test for the coil combination was performed by simulation and in vivo measurements. It could be shown that both coils are well decoupled at both operating frequencies. Whereas the maximum permissible input power of 33 W for the body array was derived from SAR simulations, the maximum permissible input power of 1.9 W for the ERC was derived from in vivo temperature measurements.

Zhipeng Cao¹, Sukhoon Oh², Philipp Ehses³, Giuseppe Carluccio⁴, Christopher M. Collins², and Mark A. Griswold^5
1Bioengineering, Penn State University, Hershey, PA, United States, ²Radiology, Penn State University, Hershey, PA, United States, ³Neuroimaging, University Hospital Tubingen, Tubingen, Germany, ⁴Electrical Engineering, The University of Illinois at Chicago, Chicago, IL, United States, ⁵Radiology, Case Western Reserve University, Cleveland, OH, United States

A proposed image reconstruction method based on compressed sensing to accelerate MR PRF temperature imaging procedure is validated on an in vivo dataset with a simple Cartesian undersampling trajectory. Results imply a novel alternative approach to ensure RF safety for high field MR systems.

Manuel Murbach^1,2, Esra Neufeld¹, Klaas P Pruessmann², and Niels Kuster^1,3
1IT'IS Foundation, Zurich, Switzerland, ²Institute for Biomedical Engineering, University and ETH Zurich, Zurich, Switzerland, ³Swiss Federal Institute of Technology (ETH), Zurich, Switzerland

This study investigates the MR induced thermal load in local temperature hotspots for various anatomical human models and positions. The simulation results are compared to temperature measurements in humans. Based on CEM43 (cumulative equivalent minutes at 43°C) tissue damage thresholds, thermally safe scan times are derived. Local thermoregulation can have a strong impact on SAR induced heating. Safety concerns arise especially for patients with disabled or partially dysfunctional perfusion abilities (e.g. the elderly, diabetics). The high estimated and measured temperature rise indicates the necessity of considering thermal dose models such as CEM43, which take into account exposure time and temperature.

Nadine N Graedel¹, Jonathan R Polimeni^1,2, Bastien Guerin¹, Borjan Gagoski³, and Lawrence L Wald^1,4
1A. A. Martinos Center for Biomedical Imaging, Dept. of Radiology, MGH, Charlestown, MA, United States, ²Harvard Medical School, Boston, MA, United States, ³Electrical Engineering and Computer Science, Massachusetts Institute of Technology, Cambridge, MA, United States, ⁴Harvard-MIT Division of Health Sciences and Technology, MA, Cambridge, United States

We constructed a human head phantom which allows 3D temperature mapping using the temperature sensitive contrast agent TmDOTMA. The phantom contains multiple tissue compartments that match those of the human head both in terms of their geometry and their electrical properties.