Ludwig Eberler¹, Juergen Nistler¹, and Volker Matschl^1
1Siemens Healthcare, Erlangen, Germany

In the abstract a procedure for the correct tuning of RF-traps is shown. The proposed procedure minimizes the influence of the measurement itself. The results of the abstract are based on simulations with CST Microwave Studio. The proposed procedure is to use the original environment to induce a high voltage at the input of the trap and determine the minimum of the current rating curve at the output of the trap. The simulations were performed on a standard Birdcage coil with two feeding cables.

Greg Hungtingdon Griffin¹, Kevan J Anderson², and Graham A Wright^1,2
1Medical Biophysics, University of Toronto, Toronto, Ontario, Canada, ²Sunnybrook Research Institute, Toronto, Ontario, Canada

Currently, safety of interventional devices is investigated using long experiments and direct measuring of induced temperature rises. A method of remotely measuring induced radiofrequency current using phase information from MRI is presented. Agreement between measurements and simulations is shown demonstrating accuracy of the remote method. This method presents a novel technique to rapidly investigate safety of different devices in vitro.

Yuan Ma¹, Gaohong Wu¹, Wei Sun¹, Joe Schaefer¹, Roee Lazebnik¹, and Glen Sabin^1
1GE Healthcare, Waukesha, WI, United States

MRI for patients with implants may cause injuries. We conducted a study analyzing FDA¡¯s MAUDE database regarding Implant MRI. We identified 87 cases of adverse events related to Implant MRI. It described deaths, life-threatening injuries, heating/burn injuries, and device malfunctions. 62% of cases were associated with active implants. 8% of identified cases were attributed to orthopedic implants. About 30% cases were associated with other types of passive metal implants or metal presence. Based on the MAUDE data, Orthopedic Implant MR imaging has relatively low occurrence of adverse events, and tends to have a low severity of harm.

Laleh Golestanirad^1,2, Graham Wright¹, and Simon Graham^1
1Medical Biophysics, University of Toronto, Toronto, Ontario, Canada, ²Laboratory of Electromagnetics and Acoustics (LEMA), Ecole Polytechnique Federale de Lausanne, Lausanne, Switzerland

 

Devashish Shrivastava¹, Timothy Hanson², Ute Goerke¹, Lance DelaBarre¹, Rachana Visaria³, Paul Iaizzo¹, Aviva Abosch¹, and JT Vaughan^1
1University of Minnesota, Minneapolis, MN, United States, ²University of South Carolina, ³MR Safe Devices LLC, Minneapolis, MN, United States

Heating near DBS lead electrodes was measured using fluoroptic temperature probes and simulated using a combination of a proton resonance frequency (PRF) shift based MR thermometry method and bioheat thermal modeling in cadaveric porcine heads during imaging with a 3T transceive head coil. The effect on the heating of the placement of the extra-cranial DBS lead with respect to the coil was investigated to reduce the heating. The feasibility of using the MR thermometry and thermal modeling together as a ‘hybrid’ approach on predicting maximum heating near the electrodes is demonstrated as an online tool to verify patient safety.

Elizabeth Hipp¹, Steffen Sammet¹, and Christopher Straus^1
1University of Chicago, Chicago, IL, United States

This educational e-poster reports the outline and design of a standard web based educational module with a concise multiple choice exam to be used for instructing medical students about basic MR and patient related safety. Direct instruction can be either interactive, with a traditional didactic lecture, or self administered online. Students regardless of their future should graduate from all physician programs with a basic understanding of MR safety, for both optimal ordering of studies and patient safety. Offering turn key materials, including the assessment, to all medical school programs will help ensure MR awareness and safety across the industry.

Jonathan Ashmore^1,2, Gareth Barker³, Ruth O'Gorman⁴, and Geoff Charles-Edwards^5
1Neuroradiology, Kings College Hospital, London, United Kingdom, ²Medical Physics, Guy's & St Thomas' NHS Foundation Trust, London, United Kingdom,³Centre for Neuroimaging Sciences, Kings College London, London, United Kingdom, ⁴Center for MR Research, University Children's Hospital, Zurich, Switzerland, ⁵Medical Physics, Guy's & St Thomas' NHS Foundation Trust, London, London, United Kingdom

A number of device manufacturers report non-standard SAR limits as conditions for the safe scanning of patients with these devices implanted. In this work we compared how the SAR was displayed on the console and what evidence of SAR levels were recorded in the DICOM header for MRI systems from three major vendors. We investigated possibilities for creating low SAR protocols that are robust in terms of never exceeding a defined non-standard SAR limit in any case.

Ulrich Katscher¹, Kay Nehrke¹, Hanno Homann¹, and Peter Börnert^1
1Philips Research Europe-Hamburg, Hamburg, Germany

A central issue of parallel RF transmission is the SAR management to ensure patient safety. As an alternative to the usually applied model-based SAR estimation, a new method has been proposed to estimate SAR from the acquired B1 maps. This B1-based SAR determination was successfully tested for quadrature (single channel) excitation in vivo and non-quadrature (multi-channel) excitation in a phantom study. This study adapts B1-based SAR determination for non-quadrature excitation in vivo. To this goal, local SAR in thighs and pelvis of a volunteer is investigated and compared with results of corresponding FDTD simulations based on the same volunteer.

Alessandro Sbrizzi¹, Hans Hoogduin², Jan J Lagendijk², Peter R Luijten², and Cornelis A van den Berg^3
1Imaging Division, UMC Utrecht, Utrecht, Utrecht, Netherlands, ²UMC Utrecht, ³UMC Utrecht, Netherlands

To compute the SAR, the electric fields generated by the RF coil should be estimated. In this work, we show how to extract this information from B1+ and treansceive phase measurements. The reconstruction of the complex z-component of the electric fields is done on the basis of a 3D model. The electromagnetic fields can be efficiently expressed in terms of few ad hoc constructed basis functions. The expansions coefficients are found by fitting the measured data to the model. Numerical simulations and in vivo measurements confirm the validity of the method for a 2ch 7T transceive birdcage headcoil.

Andre Kuehne¹, Frank Seifert¹, and Bernd Ittermann^1
1Physikalisch-Technische Bundesanstalt, Braunschweig & Berlin, Germany

Manual SAR averaging from simulated EM field data is necessary for validating the output of commercial solvers, overcoming limitations of standardized SAR algorithms and gaining flexibility and speed. We developed a GPU-accelerated SAR averaging algorithm based on FFT convolutions that is easy to implement without knowledge of GPU computing paradigms using free software for the GPU programming. It is able to utilize arbitrary averaging shapes, such as cubical or spherical volumes, and yields consistent results even at low resolution (5 mm) of the input data by employing a sub-voxel growing scheme for the averaging kernel.

Leeor Alon^1,2, Assf Tal¹, Cem Murat Deniz^1,2, Gene Young Cho^1,2, Daniel Sodickson^1,2, and Yudong Zhu^1,2
1Department of Radiology, Bernard and Irene Schwartz Center for Biomedical Imaging, New York University, New York, NY, United States, ²Sackler Institute of Graduate Biomedical Sciences, New York University, New York, NY, United States

Local specific absorption rate (SAR) quantification is important in order to ensure safety with regard to RF exposure. In this work, we used paramagnetic lanthanide complexes (TMDOTA-) to increase the sensitivity of the phantom to temperature change. The use of this phantom enabled absolute temperature measurement at a high accuracy and since the phantom was sensitive to temperature change, it enabled the accurate mapping temperature change due to smaller RF pulse exposures compared to previously shown studies. In conjunction with B1 mapping this phantom enables the local calculation of the RF coil efficiency metric.

Zhangwei Wang¹, Owen Arthurs², Desmond T.B. Yeo³, Gemma R Cook², and Fraser J Robb^1
1Coils, GE Healthcare, Aurora, OH, United States, ²Radiology, University of Cambridge, Cambridge, United Kingdom, ³GE Global Research, Niskayuna, NY, United States

Pediatric body MR imaging is limited by a lack of dedicated coils. Children have several unique physiological and physical characteristics that may influence the thermal risk during RF exposure. However, most infants are typically imaged using adult head, knee or surface coils, but SNR and SAR results have not been formally investigated. In this work, we use numerical method to evaluate an infant body model by an adult head and knee coil. Our results suggest that estimated SAR distribution varies with different clinic landmark and coil geometry, and local SAR is relatively high when infants are imaged using adult coils.

M. Dylan Tisdall^1,2, Thomas Witzel¹, Veneta Tountcheva^1,2, Jennifer A. McNab^1,2, Julien Cohen-Adad^1,2, Ralph Kimmlingen³, Philipp Hoecht⁴, Eva Eberlein³, Keith Heberlein⁴, Franz Schmitt³, Herbert Thein³, Van J. Wedeen^1,2, Bruce R. Rosen^1,2, and Lawrence L. Wald^1,2
1A.A. Martinos Center for Biomedical Imaging, Masschusetts General Hosptial, Charlestown, MA, United States, ²Radiology, Harvard Medical School, Brookline, MA, United States, ³Siemens Healthcare, Erlangen, Germany, ⁴Siemens Medical Solutions USA, Charlestown, MA, United States

We present an analysis of the SNR gains produced in high-b-value diffusion-weighted imaging using a novel 3T system with ultra-high, 300 mT/m maximum gradient amplitude (MAGNETOM Skyra CONNECTOM, Siemens Healthcare). Results are presented for both human and phantom studies with b=10k and b=20k, comparing SNR increases as a function of maximum gradient strength ranging from 40 mT/m (standard on clinical systems) to 300 mT/m.

Michael S Poole¹, Hector Sanchez Lopez¹, and Stuart Crozier^1
1School of Information Technology and Electrical Engineering, University of Queensland, Brisbane, QLD, Australia

Gradient coils have previously been designed with spread wires using the minimax|j| technique. These coils exhibit more evenly distributed temperatures than standard coils and are more efficient when limited by a minimum wire spacing. Here we investigate the application of the minimax|j| technique to whole-body shielded gradients of varying length and demonstrate that it can produce more efficient gradient coils when their length is very short.

Robert Slade¹, Zhenan Jiang², and A D Caplin^3
1Industrial Research Limited, Lower Hutt, New Zealand, ²Industrial Research Limited, ³Imperial College, London, United Kingdom

The use of 2G HTS (YBCO) Roebel cable for MRI gradient coils was theoretically assessed. Planar coils were identified as the most suitable geometry. A phenomenological model was developed to scale AC losses observed in small test coils at 77K and self field to the desired size, background field and cryogenic operating temperature. The refrigerator input power required to balance these losses was estimated. Reduction in power consumption compared with copper of ~10 appears feasible for head-size coils using 9x2mm Roebel cable, but more strands and higher current capacity are required to show benefit over copper at whole body scale.

Limei Liu¹, Hector Sanchez Lopez¹, Michael Poole¹, Feng Liu¹, and Stuart Crozier^1
1the University of Queensland, Brisbane, Queensland, Australia

the impact of the central gap size is studied in this work in terms of the eddy current effects in a split whole-body MRI system which is designed for the PET-MRI multi-imaging technology. An optimal central gap size is found by analyzing the gradient performance and the eddy current effects as a function of the central gap size. The split MRI system with this central gap size could generate the smallest eddy current effects with good gradient performance. The findings in this work may provide indicators of potentially useful system configuration for the PET-MRI systems.

Patrick Vogel^1,2, Martin A. Rückert^1,2, Peter Klauer^1,2, Walter H. Kullmann², Peter M. Jakob^1,3, and Volker C. Behr^1
1Experimental Physics 5 (Biophysics), University of Würzburg, Würzburg, Germany, ²Electrical Engineering, University of Applied Sciences Würzburg-Schweinfurt, Schweinfurt, Germany, ³Research Center Magnetic Resonance Bavaria (MRB) e.V., Würzburg, Germany

Magnetic Particle Imaging is a new imaging approach which can directly image super-paramagnetic nano particles. For 3D imaging we present a new approach which encodes with a traveling wave in one direction and a combination of frequency mixing and slicing for the other two dimensions. The advantage of this traveling wave approach is the possibility to arbitrarily increase the FoV in one direction without increasing the scanning time or the SAR.

Mir Farrokh Salek¹, and Arthur Gmitro^1
1Radiology, University of Arizona, Tucson, AZ, United States

Results obtained from MRI could be corroborated or complemented if they are accompanied by other independent measurements. In many applications, this combination of different methodologies would be optimum if they are done simultaneously on the subject. We report on an instrument that allows simultaneous MR and optical fluorescence imaging of mouse dorsal skin-fold window chamber. This instrument operates by relaying the optical image outside the magnet bore. Using this methodology we are able to measure vascular permeability of albumin dual labeled with GdDTPA and an optical fluorescent contrast agent.

Ileana Hancu¹, Keith Park¹, and Robert Darrow^1
1GE Global Research Center, Niskayuna, NY, United States

A paradigm is presented here, in which the definition of the region of interest center in an MRI scan is automated. This process relies on a probing RF coil, tuned high. A passive RF coil, also tuned high, marks the center of the receive array. As the patient approaches the scan position, and the probing and marker coils come in close proximity, the signal received by the probing coil increases, with the maximum signal obtained when the two coils overlap. We show that precision better than 1cm can be achieved in finding the Rx coil marker using this approach.

Panu T. Vesanen¹, Jaakko O. Nieminen¹, Koos C.J. Zevenhoven¹, Juhani Dabek¹, Juho Luomahaara², Juha Hassel², Jari Penttilä³, Andrey V. Zhdanov¹, Fa-Hsuan Lin^1,4, Yi-Cheng Hsu^1,5, Lauri T. Parkkonen⁶, Juha Simola⁶, Antti I. Ahonen⁶, and Risto J. Ilmoniemi^1
1Department of Biomedical Engineering and Computational Science, Aalto University, Espoo, Finland, ²VTT Technical Research Centre of Finland, Espoo, Finland, ³Aivon Oy, Espoo, Finland, ⁴Institute of Biomedical Engineering, National Taiwan University, Taipei, Taiwan, ⁵Department of Mathematics, National Taiwan University, Taipei, Taiwan, ⁶Elekta Oy, Helsinki, Finland

Ultra-low-field MRI (ULF MRI) in a microtesla order B0 field utilizes superconducting quantum interference devices (SQUIDs) to measure the MRI signals. Furthermore, magnetoencephalography (MEG) employs SQUIDs to measure the weak magnetic fields generated by the human brain. Based on a commercial whole-head 306-channel MEG device, we present here a 72-channel hybrid device capable of both MEG and ULF MRI. We describe our experimental setup that features a superconducting polarizing coil and field tolerant all-planar SQUID sensors. As a result of our work, we present an image of human hand with an in-plane resolution of 4 mm x 3 mm.

Stephan Biber¹, Katrin Wohlfarth¹, John Kirsch¹, and Andreas Schmidt^1
1Siemens Healthcare, Erlangen, -, Germany

B0 variation induced by the spatially inhomogeneous susceptibility distribution of the patient are a major challenge for application that rely heavily on B0 homogeneity such as EPI or spectral fat suppression techniques. In the abdomen, the major sources of B0-inhomogeneity are the lungs and the strongly asymmetric anatomy of the heart, while in the head, the sinuses and mouth generate major inhomogeneities. Another vulnerable region for B0 problems that has hardly been addressed is the transition from the upper thorax to the neck and head region. The shoulders are a strong discontinuity for the z-oriented B0 field and generate spatially large inhomogeneity. If the patient’s anatomy does not allow the ability to place the neck region completely flat on the table, B0 fields penetrating in and out of the patient in the posterior neck region generate additional B0 inhomogeneity. This can become an issue, e.g. for spectral fat suppression techniques applied to cervical spine imaging. Susceptibility pads or other passive shims have been proposed for various applications and are partly commercially available. Nevertheless, most of the commercial products are bulky, costly and generate additional space limitations inside a local coil. Recently, the use of local shim coils and shim coil arrays for both static shimming and dynamic shimming especially at ultra high fields (UHF) has been proposed. This work presents a very simple and effective approach to overcome static B0-inhomogeneities in the cervical spine region by using a single channel local shim coil located inside the housing of a head neck coil.

Chad Tyler Harris¹, William B Handler¹, Brian Dalrymple¹, Frank Van Sas¹, Yonathan Araya², Timothy J Scholl^2,3, and Blaine A Chronik^1,3
1Physics and Astronomy, University of Western Ontario, London, Ontario, Canada, ²Medical Biophysics, University of Western Ontario, London, Ontario, Canada, ³Imaging Research Laboratories, Robarts Research Institute, London, Ontario, Canada

Delta relaxation enhanced magnetic resonance (dreMR) is a method that has been shown to drastically improve signal specificity between the bound and unbound states of targeted contrast agents. The method requires a supplementary "Bo insert coil" to modulate the main magnetic field within an otherwise unmodified superconducting system. Magnetic shielding is a major challenge in the design and construction of these insert coils. In this work, we investigate improvements in shielding capability by including primary coil construction details (i.e. winding misplacements, wire connections) in the design of the shield.

Andrey Zhdanov¹, Jaakko O. Nieminen¹, Panu T. Vesanen¹, Koos C.J. Zevenhoven¹, Juhani Dabek¹, Juho Luomahaara², Juha Simola³, Antti I. Ahonen³, and Risto J. Ilmoniemi^1
1Department of Biomedical Engineering and Computer Science, Aalto University School of Science, Espoo, Finland, ²VTT Technical Research Centre of Finland, Espoo, Finland, ³Elekta Oy, Helsinki, Finland

Ultra-low-field (ULF) MRI using microtesla imaging fields posesses a number of advantages over conventional high-field MRI, such as low cost, better patient safety, higher immunity to imaging field inhomogeneities, silent operation and enhanced T1 contrast. ULF MRI experimental setup at Aalto University contains superconducting components that are placed close to the imaging volume: superconducting niobium shields protecting sensors from the prepolarizing field and superconducting polarizing coil. We estimate the impact of these components on the homogeneity of the imaging field using finite element numerical simulations and devise a strategy for their optimal placement.

Matthew J. Riffe¹, Daniel Neumann², Colin Blumenthal³, Gregory Lee⁴, Nicole Seiberlich¹, and Mark A. Griswold^1,4
1Biomedical Engineering, Case Western Reserve University, Cleveland, Ohio, United States, ²Research Center for Magnetic Resonance Bavaria (MRB), Wuerzburg, Germany, ³Electrical and Computer Engineering, Ohio State University, Columbus, Ohio, United States, ⁴Radiology, Case Western Reserve University, Cleveland, Ohio, United States

For improved performance, magnetic field monitoring (MFM) requires an array of hetero-nuclear transceiver NMR probes, which requires a separate specialized multi-frequency transceiver system to acquire the MFM signals. We propose that a wireless magnetic field monitoring system would allow the hetero-nuclear MFM signals to be collected with the narrow-band ¹H MRI receivers, eliminating the need for this extra transceiver. To demonstrate feasibility, initial results from a four-probe receive-only wireless MFM system are presented. A spiral TrueFISP trajectory with a 256kHz bandwidth is measured with the wireless MFM system, and phantom images are reconstructed using the measured trajectory.

Michael S Poole¹, Hector Sanchez Lopez¹, and Stuart Crozier^1
1School of Information Technology and Electrical Engineering, University of Queensland, Brisbane, QLD, Australia

The minimax|j| coil design method produces the most efficient coils when limited by minimum wire spacing. This method was used to design shim coils. An increase in shim strength of between 22 and 92% for the same minimum wire spacing over standard designs in these coils was observed.

Hector Sanchez-Lopez¹, Michael Poole¹, Ewald Weber¹, Limei Liu¹, and Stuart Crozier^1
1ITEE, The University of Queensland, Brisbane, QLD, Australia

Eddy currents are one of the main causes of deleterious cross-talk within hybrid MRI scanners such as (IGRT-MRI) Image Guided Radiotherapy-MRI or PET-MRI systems. Currents induced in the conducting parts of scanners produce acoustic noise, power heating, magnetic field asymmetries. In this paper we present a new fast and efficient eddy current simulation method which combines current densities expressed as normalized Fourier series and linear basis functions. The new method is capable of accurately simulating currents induced in thick cylinders of finite length (such as a cryostat) and thin surfaces of arbitrary shape by coils of arbitrary geometry.

Peter T. While¹, Michael Poole², Larry K. Forbes¹, and Stuart Crozier^2
1School of Mathematics and Physics, University of Tasmania, Hobart, Tasmania, Australia, ²School of Information Technology and Electrical Engineering, University of Queensland, Brisbane, Queensland, Australia

A method is presented for the theoretical design of gradient coils with minimum maximum temperature. A previously reported analytical model is used for predicting the spatial temperature distribution and sequential quadratic programming is used to minimize peak temperature directly. The method is applied to both symmetric and asymmetric gradient coils and considerable reductions in maximum temperature (up to 50%) are achieved at no cost to coil performance. The new winding patterns are characterized by a “fish-eye” effect to smooth the hot spot regions. The final coil solutions are dependent on the assumed thermal material properties rather than direct coil spreading.

Silke M. Lechner-Greite¹, Jean-Baptiste Mathieu², Seung-Kyun Lee³, Bruce C. Amm⁴, Thomas K. Foo⁵, John F. Schenck⁶, Matt A. Bernstein⁷, and John Huston^7
1Diagnostics and Biomedical Technologies, GE Global Research Europe, Garching n. Munich, Germany, ²Electromagnetics & Superconductivity Laboratory, GE Global Research Niskayuna, Albany, NY, United States, ³MRI Laboratory, GE Global Research Niskayuna, Albany, NY, United States, ⁴Biomedical and Electronic Systems Laboratory, GE Global Research Niskayuna, Albany, NY, United States, ⁵Diagnostics and Biomedical Technologies, GE Global Research Niskayuna, Albany, NY, United States, ⁶MRI Technologies & Systems, GE Global Research Niskayuna, Albany, NY, United States, ⁷Mayo Clinic, Rochester, MN, United States

We report on the design and eddy current simulation of a head-only shielded gradient coil prototype consisting of asymmetric transverse gradients and a symmetric axial gradient. Eddy currents induced in a conductive cylinder surrounding the gradient coil were evaluated during prototyping stage using eddy image calculation and certain higher-order eddy currents were suppressed by design to ensure good image quality for applications like diffusion weighted imaging. Finite element simulations in static, frequency, and transient domain confirmed the level of higher-order harmonic field distortion predicted by eddy current image computation, and revealed the frequency content, amplitude, and time evolution of the eddy current field in the imaging field of view. The spatial linearity of the gradient field was found to be significantly affected by the time-dependent higher-order harmonic eddy current terms.

Harald Braun¹, Susanne Ziegler¹, Daniel H Paulus¹, Jens U Krause¹, and Harald H Quick^1
1Institute of Medical Physics, University of Erlangen-Nürnberg, Erlangen, Bavaria, Germany

Simultaneous whole-body PET/MR hybrid imaging has become clinical reality. Usually in MRI and PET data is acquired in a multi-station approach, where the patient table is held at a constant position. This bears some inherent shortcomings: varying sensitivity (PET), distortion in z-direction (MRI), combination artifacts between individual bed positions, etc.. To overcome these shortcomings, we introduce a data acquisition and post-processing approach with continuous table motion (CTM). CTM PET/MR data acquisition was evaluated with a custom-built large field-of-view phantom and on a clinical patient. This approach for the first time enables simultaneous whole-body PET/MR hybrid imaging during continuous table movement.

Daniel Burje Chonde^1,2, and Ciprian Catana^1
1Martinos Center for Biomedical Imaging, Charlestown, MA, United States, ²Biophysics, Harvard University, Cambridge, MA, United States

An estimation of the radiotracer blood input function is essential for parametric estimation from dynamic PET data. Traditionally it is measured through invasive methods; however, it can be acquired through image-based methods. Using MR-based segmentation is thought to provide the most accurate arterial definition, however registration is difficult in sequential imaging. In a Simultaneous MR-PET system many of the issues with sequential imaging are irrelevant. This work presents a novel framework in which to derive a PET image-based input function using multiple MR sequences with the practical consideration of limiting total scan time.

Isabel Dregely¹, Ambros Beer¹, Axel Martinez-Moeller¹, Sebastian Fuerst¹, Matthias Eiber¹, Gaspar Delso¹, Hua-Lei Zhang¹, Michael Souvatz¹, Alexander Drzezga¹, Sibylle Ziegler¹, Stephan G Nekolla¹, and Markus Schwaiger^1
1Nuclear Medicine, Klinikum rechts der Isar der TU München, Munich, Bavaria, Germany

Simultaneous PET/MR is a technical revolution. However, the scientific and clinical added value by simultaneous imaging has yet to be proven. The goal of this presentation is to give the reader the necessary background to understand, critically evaluate and participate in this exciting development in multi-modality imaging.

Katerina Dikaiou¹, Florian Stuker¹, Jan Klohs¹, Andreas Elmer¹, Jorge Ripoll^1,2, and Markus Rudin^1,3
1Institute for Biomedical Engineering, University and ETH Zurich, Zurich, Zurich, Switzerland, ²Institute for Electronic Structure and Laser – FORTH, Crete, Greece, ³University of Zurich, Institute of Pharmacology and Toxicology, Zurich, Switzerland

The combination of fluorescence molecular tomography (FMT) with magnetic resonance imaging can provide complementary structural, functional and molecular information in vivo. Here, a new generation of a hybrid FMT/MR system for mouse imaging is presented. Proof of principle of this system is shown on a transgenic mouse model of Alzheimer’s disease using a dye known to bind to beta-amyloid plaques. High-quality datasets from both modalities were acquired, and we could successfully distinguish wild type from transgenic animals in vivo with FMT. MRI revealed microbleeds indicative of vascular pathology. Our results were validated ex vivo.

Hua-Lei Zhang¹, Sebastian Fürst¹, Axel Martinez-Möller¹, Isabel Dregely¹, Alexandra Bartel¹, Markus Schwaiger¹, and Stephan Nekolla^1
1Klinikum rechts der Isar der TU München, Munich, Bavaria, Germany

Multi-channel receiver coils are mandatory to obtain high-quality MR images. This study aims to evaluate regional effects from state-of-the-art MR coils not optimized for hybrid imaging on PET and to address whether rather demanding adjustments for usage in MR/PET are needed. Adding a 32-element coil set introduced PET activity underestimation but maintained the signal homogeneity in MR/PET, while severe inhomogeneity and preserved overall activity counts was found in CT-based attenuation corrected PET images. The findings provide insights on how to make compromises to obtain high-quality MR images without degrading PET activity concentration when using coils not specifically optimized for MR/PET.

Yujuan Zhao¹, Tiejun Zhao², Daniel Stough¹, Chad Harris³, William Handler³, Hai Zheng¹, Shaohua Lin⁴, Fernando Boada¹, Blaine Chronik³, and Tamer Ibrahim^1
1University of Pittsburgh, Pittsburgh, Pennsylvania, United States, ²Siemens Medical Solutions, Pittsburgh, Pennsylvania, United States, ³University of Western Ontario, London, Ontario, Canada, ⁴ANSYS, Pittsburgh, Pennsylvania, United States

Synopsis: In this work, a new eddy current simulation method was presented. The eddy current simulation method presented in this paper is verified by the measurement results, EPI phantom images as well as localized excitation images on human subjects. The agreement of experimental and numerical data demonstrates the potential of using simulation methods in the study of eddy current characterization and in designing methods/techniques that can minimize eddy current.

Hector Sanchez-Lopez¹, Ewald Weber¹, Michael Poole¹, Limei Liu¹, and Stuart Crozier^1
1ITEE, The University of Queensland, Brisbane, QLD, Australia

The RF shield aims to prevent electromagnetic interactions between the RF coil and the electromagnetic environment in which the coil is immersed. The slits in the RF shield cut the path of the eddy current’s flow, thus ameliorating deleterious effects such as mechanical vibration and power heating. This last effect can significantly deteriorate the RF coil. In this paper we present an integrated design RF-shield-gradient coil in which power loss due to eddy currents is reduced by more than 8 times than of a conventional design. We demonstrated that an integrated design process conduces toward novel gradient coil.

Alex A Bhogal¹, Jos Koonen², Jeroen Siero³, Vincent Boer³, Dennis Klomp³, Peter Luijten³, and Hans Hoogduin^3
1Radiology, University Medical Center Utrecht, Utrecht, Utrecht, Netherlands, ²Philips, ³Radiology, University Medical Center Utrecht

Dynamic Slice Based shimming at high field is gaining interest. Here, a novel method is presented to measure and characterize EC fields for pre-emphasis and eddy current compensation without the need for field probes or projection based measurements. Complete 3D datasets are acquired providing complete spatio-temporal characterization of eddy field self and cross terms up to third order. Results are used to calibrate a Dynamic Shim Updating (DSU) unit for slice-based applications at 7T.

Ramez E. N. Shehada¹, Rohan More¹, Reza Imani¹, Wudi Zhou¹, Micah Meulmester¹, Benjamin Coppola¹, Jon Dietrich¹, Richard Williamson¹, and Ali Dianaty^1
1CRMD, St. Jude Medical, Sylmar, California, United States

Gradient-induced vibrations can fatigue the components of MRI-conditional active-implantable medical devices (AIMD) leading to their failure. A non-contact vibrometer was used in a special fixture to measure the vibrations of various AIMD components in clinical 1.5T MRI scanners. The frequency range of the vibrations ranged from 0-2kHz with a maximum displacement of 25um. The vibration values were then programmed into a computerized shaker-table that was used to aggressively vibrate the AIMD for longer periods of time after which the AIMD was checked for damage. This study presents a new method for characterizing the vibrations and assessing their effects on AIMD.

Mark C Oswood^1,2
1Consulting Radiologists, Ltd, Minneapolis, MN, United States, ²Radiology, Abbott-Northwestern Hospital, Minneapolis, MN, United States

We report a case of MR imaging safety hazard due to unsuspected metal threads (lurex) which were woven into a patient’s shirt. The patient’s shirt was burned during lumbar MR imaging at 1.5T, but the patient did not suffer any injury. Because of the difficulty of detecting metal-containing fabric during routine safety screening, MR imaging facilities should consider requiring patients to change into a metal-free cloth gown prior to MR imaging.

Janneke Ansems¹, Anja G van der Kolk², Hugo Kroeze², Nico AT van den Berg³, Gert-Jan de Borst⁴, Peter R Luijten², Andrew G Webb⁵, W Klaas Jan Renema⁶, and Dennis WJ Klomp^2
1Radboud University Nijmegen Medical Center, Nijmegen, Netherlands, ²Department of Radiology, University Medical Center Utrecht, Utrecht, Netherlands,³Department of Radiotherapy, University Medical Center Utrecht, Utrecht, Netherlands, ⁴Department of Vascular Surgery, University Medical Center Utrecht, Utrecht, Netherlands, ⁵Department of Radiology, C.J. Gorter Center for High Field MRI, Leiden University Medical Center, Leiden, Netherlands,⁶Department of Radiology, Radboud University Nijmegen Medical Center, Nijmegen, Netherlands

At increasing magnetic field strength, safety issues regarding RF heating of metallic implants become increasingly important. Although many implants have been tested at lower field strengths, these tests are relatively lacking at (ultra)high field. Based on theoretical assumptions regarding low Q-values, being the dominant factor in tissue heating at (ultra)high field, we tested our theory that scanning metallic implants like stents is RF-safe. Using both experimental Q-value measurements, temperature experiments using commonly used vascular stents scanned at 7.0 Tesla MRI with 3-times SAR-limit, displacement measurements and an in vivo 7T experiment, we show that scanning peripheral stent grafts is RF-safe.

Julian Maclaren¹, Michael Herbst¹, and Maxim Zaitsev^1
1University Medical Center Freiburg, Freiburg, Germany

This educational e-poster is a guide to modifying devices and equipment to ensure MR compatibility. Basic physics relating to MR compatibility is explained, practical tips for device modification are given, and a collection of compatibility tests are described.

Joep Wezel^1,2, Wyger Brink¹, Bert Jan Kooij², and Andrew Webb^1
1C.J. Gorter center, Department of Radiology, Leiden University Medical Center, Leiden, Zuid-Holland, Netherlands, ²Microwave Technology and Systems for Radar, Technical University Delft, Delft, Zuid-Holland, Netherlands

The aim of this study is to determine whether scanning a person with a titanium dental retainer wire is safe at 7 Tesla. Touching the wire with the tongue causes loading of the wire, reducing the Q factor, but simultaneously brings the RF half-wavelength closer to the wire dimensions. Simulations with both phantom and head model suggest the latter effect is dominant. The overall conclusion is that, provided that a small air gap is present between wire and tongue, no tissue heating results and the use of such dental implants is safe.

Yacine Noureddine^1,2, Oliver Kraff^2,3, Mark E. Ladd^2,3, Gregor Schaefers¹, Karsten H. Wrede⁴, and Andreas K. Bitz^2,3
1MR:comp GmbH, MR Safety Testing Laboratory, Gelsenkirchen, NRW, Germany, ²Erwin L. Hahn Institute for Magnetic Resonance Imaging, University Duisburg-Essen, Essen, NRW, Germany, ³Department of Diagnostic and Interventional Radiology and Neuroradiology, University Hospital Essen, Essen, NRW, Germany, ⁴Clinic for Neurosurgery, University Hospital Essen, Essen, NRW, Germany

RF-induced heating as a result of electric field elevations in tissue close to metallic aneurysm clips is a major concern with respect to the safety of patients with these implants. In this study, a detailed investigation of the orientation of the elongated implant with respect to the polarization of the electric field was performed. Polarization and incident angle of a uniform plane wave were varied in steps of 90 degrees utilizing numerical simulations. Additionally, field measurements were performed and compared to the simulations.

Daniel James Lee¹, and Paul M Glover^1
1Physics and Astronomy, University of Nottingham, Nottingham, Nottinghamshire, United Kingdom

Multi-transmit systems are becoming more popular as scanners move to higher field strengths, but one of the main costs is purchasing RF amplifiers. This expense increases with both the number of channels and the peak power of the amplifiers. Using a combination of some simple simulations and basic MR physics it is possible to establish a “rough” estimate of the peak power required from amplifiers for multi-transmit systems. The values obtained from such calculations are two to three times higher than amplifier values currently in use, but still allow for an informed decision when buying a multi-transmit system.

Aurélien MASSIRE¹, Martijn CLOOS^1,2, Michel LUONG², Alexis AMADON¹, Alexandre VIGNAUD³, Christopher J. WIGGINS¹, Denis LE BIHAN¹, and Nicolas BOULANT^1
1DSV I2BM NeuroSpin, CEA, Gif-sur-Yvette, France, ²DSM IRFU SACM, CEA, Gif-sur-Yvette, France, ³Siemens Healthcare, Paris, France

Numerical simulations were performed to investigate the compliance of the specific absorption rate versus the temperature guidelines for the human head in MRI procedures utilizing parallel transmission at 7 T. Computations using finite elements and finite difference time domain techniques were implemented on a human head model to perform the electromagnetic and thermal simulations respectively. Temperature evolution throughout the head was calculated by integrating numerically the Pennes’ bioheat equation for 1000 parallel transmission scenarios corresponding to random static RF configurations, for the synthesized circularly polarized (CP) mode, and for two realistic Transmit-SENSE RF exposures.

Hanno Homann¹, Inagmar Graesslin¹, Ulrich Katscher¹, Peter Vernickel¹, Kay Nehrke¹, and Peter Börnert^1
1Philips Research Laboratories, Hamburg, Germany

Parallel transmission enables control of the RF transmit field in time and space. Hence, the B1-field and the SAR distribution can be influenced. To evaluate the potential for SAR reduction, numerical RF field simulations were carried out for an 8-channel Tx body coil and 9 volunteer body models. RF shimming was observed to reduce SAR. Using the volunteer-specific SAR constraints, a further SAR reduction could be achieved. Furthermore, a generalized model representing a multitude of patient anatomies was applied. It was demonstrated that such a generalized approach does not necessarily entail increased computation times or severe compromises in B1-performance.

Xin Chen¹, Yong Wu², Zhen Yao², Michael Steckner¹, and Robert Brown^2
1MR, Toshiba Medical Research Institute USA, Inc., Mayfield Village, OH, United States, ²Department of Physics, Case Western Reserve University, Cleveland, OH

Numerical simulations of SAR have been widely used to investigate MRI RF safety. Although studies have covered multiple human models , imaging landmarks , and transmit body coil types , more clinical imaging scenarios remain to be investigated, such as patient scanned as “head first” or “feet first”. Eddy current induced in conductive imaging subject by RF magnetic field is asymmetric even with a perfectly symmetric phantom and coil. Human tissue heterogeneity and asymmetry add even more complexity to this phenomenon. In this work, we used FDTD numerical simulations to study a generic body transmit coil loaded with a digital human model. Simulations were performed for 11 imaging landmarks from head to toe, both “head first” and “feet first”. Significant differences in peak local SAR were observed for two loading directions.

Leeor Alon^1,2, Cem Murat Deniz^1,2, Ryan Brown¹, Daniel Sodickson^1,2, and Yudong Zhu^1,2
1Department of Radiology, Bernard and Irene Schwartz Center for Biomedical Imaging, New York University, New York, NY, United States, ²Sackler Institute of Graduate Biomedical Sciences, New York University, New York, NY, United States

In Magnetic Resonance Imaging, local and global specific absorption rates (SAR) are metrics needed to ensure patient safety. Even though global SAR can be effectively monitored in-vivo for single and multi-channel transmit systems, local SAR is much harder to assess. Often, Local SAR estimation utilizes numerical simulation software to model particular coil setups and calculate the electromagnetic fields associated with the simulated coil setups. In this work, it is shown that even relatively slight inaccuracies in the modeled coil geometry could significantly alter the E field and SAR distribution while leaving the maximum B1+ field change relatively unperturbed. This alteration of the E field and SAR distribution are also seen to increase with field strength, suggesting possible shortcomings of using simulation software and comparing the B1+ maps of simulations and experiments to account for RF safety of coil arrays.

Daniel K. Stough¹, and Tamer Ibrahim^2
1University of Pittsburgh, Pittsburgh, PA, United States, ²University of Pittsburgh

The improvement of MR coil signal at UHF requires a gamut of solutions to overcome hindrances. B₁ shimming provides a straight forward mechanism for RF optimization, but can be tricky to implement in practice. The learning experiences encountered in the implementation of shimming for multi-transmit 7T coils will discussed as well as background material for real-time computation, as learned in the development of a shimming optimization software program.

Jin Jin¹, Feng Liu¹, Ewald Weber¹, and Stuart Crozier^1
1The School of Information Technology and Electrical Engineering, The University of Queensland, Brisbane, Queensland, Australia

The substantial challenges for high-field magnetic resonance imaging are the control of transmit magnetic field (B₁⁺) homogeneity and the specific absorption rate (SAR), so that the potential for higher signal-to-noise ratio (SNR) at high fields can be realised. To address these challenges, we demonstrate the use of the inverse field-based approach for simultaneous mapping of the magnetic and the concomitant electric field distributions within the imaged subject. Using a simple yet effective RF shimming algorithm, dubbed “SNR shimming”, the complete knowledge of the electromagnetic field distribution enables us to more effectively regulate B₁-inhomogeneity, maximum local SAR and local SNR.

Volkan Emre Arpinar¹, and L Tugan Muftuler^1,2
1Department of Neurosurgery, Medical College of Wisconsin, Milwaukee, WI, United States, ²Center for Imaging Research, Medical College of Wisconsin, Milwaukee, WI, United States

In the work full wave electromagnetic modeling was used to study and compare the performances of transformer, capacitive and inductive decoupling in RF coil arrays. We also investigated the sensitivity of decoupling to variations in component values. Such variations might arise from manufacturing tolerances as well as aging or heating, which may degrade the performance of the coil and reduce image quality.

Lukas Winter¹, Celal Özerdem¹, Helmar Waiczies¹, and Thoralf Niendorf^1,2
1Berlin Ultrahigh Field Facility (B.U.F.F.), Max-Delbrueck-Center for Molecular Medicine, Berlin, Germany, ²Experimental and Clinical Research Center (ECRC), Charité - University Medicine Campus Berlin Buch, Berlin, Germany

Combining RF hyperthermia and MR imaging is conceptually appealing to pursue spatially and temporally controlled and monitored RF heating. The benefits of this approach could be used as an adjunctive therapy for established cancer treatments including radiotherapy and chemotherapy , targeted drug delivery and targeted MR contrast agent delivery. This simulation study evaluates a stripline and dipole antenna design for RF heating at 1.5T, 3.0T, 7.0T, 9.4T and 11.7T MR frequencies.

Frank Seifert¹, Tomasz Lindel¹, and Peter Ullmann^2
1Physikalisch-Technische Bundesanstalt (PTB), Berlin, Germany, ²Bruker BioSpin MRI GmbH, Ettlingen, Germany

Controlling local SAR is crucial for patient safety in parallel transmission MRI. EM field simulations are basic tools to determine multi-channel EM field distributions necessary for pTX RF pulse calculation and for predicting RF power deposition in the human body. Here we present a reliable simulation procedure including realistic models of coil losses and matching circuits allowing experimental validation in absolute units. The efficient implementation is based on post processing of FDTD data, i.e. complex valued E, H and J distributions for each channel in conjunction with the complex impedance matrix calculated from steady state currents and voltages at the feeding ports of the coil array.

Volker Matschl¹, Juergen Nistler¹, and Sandra Weiss^2
1Siemens Healthcare, Erlangen, Germany, ²University Erlangen-Nuernberg, Germany

The following abstract demonstrates a 3x8 element pTX array bodycoil which is also stacked in z-direction. The coil design is based on capacitive decoupling in axial and tray-shielding in circumferential direction. Properties like element decoupling, coil efficiency and power consumption were investigated.

Ileana Hancu¹, Seung-Kyun Lee¹, W. Thomas Dixon¹, Laura Sacolick², Ricardo Becerra³, Zhenghui Zhang³, Graeme McKinnon³, and Vijayanand Alagappan^4
1GE Global Research Center, Niskayuna, NY, United States, ²GE Global Research Center, Munich, Germany, ³GE Healthcare, Waukesha, WI, United States,⁴GE Healthcare, Aurora, OH, United States

Shading is a common issue at 3T, recently shown to be mitigated by elliptical, dual or multiple drive transmit technology. In this study, breast shading was investigated, and attributed to eddy currents induced in a conductive material. An alternative correction approach was developed, based on selective un-blocking and up-tuning of a receive element of a standard 8 channel breast receive array during the transmit phase. This field focusing (or passive parallel transmit) approach resulted in more uniform B1+, better fat suppression and higher SNR, all with lower specific absorption rate.

Rock Hadley¹, Jim Stack², John Roberts³, Robb Merrill³, Dennis Parker³, and Glen Morrell^3
1Radiology, University of Utah, Salt Lake City, Utah, United States, ²Remcom Inc, ³Radiology, University of Utah

We present a novel hybrid non-resonant RF transmit coil design which uses a twisted microstrip configuration and distributed lumped capacitors to acheive linear phase of the magnetic field along the long axis of the coil. This coil may be useful for parallel transmission and gradientless imaging.

Can Akgun¹, Lance DelaBarre², Carl Snyder², Kamil Ugurbil², Anand Gopinath³, and John Thomas Vaughan^2
1Center for Magnetic Resonance Research, University of Minnesota, Minneapolis, MN, United States, ²Center for Magnetic Resonance Research, University of Minnesota, ³Department of Electrical and Computer Engineering, University of Minnesota

The microstrip transmission line has been a popular coil element of choice in multi-element transceiver arrays due to its’ bi-directional current path. An important consideration in microstrip design is the ability to control the transmit field propagation in the transaxial plane. Here in this work, ground plane sidewalls are designed and incorporated as part of the microstrip coil element. Introducing ground sidewalls between microstrip elements can reduce decoupling with neighboring elements, can contain the transmit field near the source, and provide a more efficient coil element.

Bei Zhang¹, Andrew B Rosenkrantz², Daniel K. Sodickson¹, Samir S Taneja², Cornel Stefanescu¹, and Graham C Wiggins^1
1The Bernard and Irene Schwartz Center for Biomedical Imaging, NYU Medical Center, New York, NY, United States, ²Department of Radiology, NYU Langone Medical Center, New York, NY, United States

Prostate imaging could benefit from the increased MR sensitivity at 7 Tesla, but such deep torso imaging is challenging due to extreme RF inhomogeneity and is relied on parallel transmit and RF shimming, which bring complexity to the equipment requirement and the acquisition of data. We propose that it is possible to achieve excitation in the prostate with only two transmitter elements. Traditional loops and radiative dipole antennas were evaluated through simulation, and simulations are used to help design and build a two-element transmit-receive plus six-channel receive-only array for prostate imaging at 7 Tesla and tested it in human imaging.

Christopher John Wiggins¹, Marie-France Hang¹, Alexis Amadon¹, Martijn Cloos¹, Nicolas Boulant¹, Michel Luong², Guillaume Ferrand², and Karl Edler^1
1LRMN, CEA/NeuroSpin, Gif-sur-Yvette cedex, France, ²Irfu, CEA/DSM, Gif-sur-Yvette cedex, France

Most transmit array coils for imaging of the human head are based on cylindrical designs. This arrangement leaves most elements at a distance from the superior surface of the brain. We present here a combination of dipoles (on a cylindrical surface) and geometrically decoupled loops (on a plane tranverse to the axis of the cylinder) to bring some elements closer to the superior surface of the head.

Pedrm Yazdanbakhsh¹, Klaus Solbach¹, Andreas K Bitz², and Mark E Ladd^2
1HFT, Duisburg-Essen University, Duisburg, NRW, Germany, ²Erwin L. Hahn Institute for Magnetic Resonance Imaging, Essen, Germany

This abstract presents a variable power combiner which is designed and fabricated for our 7-Tesla Magnetic Resonance Imaging (MRI) system. Using this variable power combiner our 16-channel coil (Antenna) array system, consisting of a 16×16 Butler Matrix and 16-channel coil array, can be excited at different power distributions with prescribed both amplitudes and phases. Vector modulator phase and amplitude weights are calculated based on the S-matrix of the combiner network and the prescribed output amplitudes and phases.

Weinan Tang¹, Hongyu Sun¹, Zechong Xiong¹, and Weimin Wang^1
1Institute of Quantum Electronics, School of Electronic Engineering and Computer Science, Beijing, Beijing, China

We suggest some ideas for building an inexpensive, scalable MR receiver with digital optical transmission. It consists of a RF front end at the magnet housing and a control interface at the electronics room. The MR signals from the preamplifiers are directly sampled, decimated, and transferred via an optical fiber. A high speed PCI express interface is implemented to connect the receiver to a reconstruction computer. In conjunction with a home built MRI system, this modular receiver has been verified for good performance and featured with scalability, high speed, and low cost.

Ying-Hua Chu¹, Boris Keil², Wei-Chao Chen³, Wen-Jui Kuo⁴, Fa-Hsuan Lin^1,2, and Fa-Hsuan Lin^5
1Institute of Biomedical Engineering, National Taiwan University, Taipei, Taiwan, ²Athinoula A. Martinos Center for Biomedical Imaging, Massachusetts General Hospital, Harvard Medical School, Charlestown, MA, United States, ³SDI corporation, Chang-Hua, Taiwan, ⁴Institute of Neuroscience, National Yang Ming University, Taipei, Taiwan, ⁵Department of Biomedical Engineering and Computational Science (BECS), Aalto University, Espoo, Finland

In order to tailor to two-dimensionally accelerated parallel MRI in 3D brain imaging, we develop a 32-channel head coil array with circularly symmetric geometry at 3T. Specifically, 32 curved trapezoidal RF coils were arranged evenly to cover the whole brain. RF coils are decoupled by overlapping and low-noise preamplifiers. The mechanical housing of the array was designed to ensure easy access. Preliminary structural images show good sensitivity and SNR over the whole brain. Nine-fold accelerated structure image (3x3) shows good white/gray matter contrast.

xinyuan wang¹, Rui Li¹, Cecil Hayes², Niranjan Balu³, Xihai Zhao⁴, and Chun Yuan^2
1biomedical engineering of tsinghua university, Center for Biomedical Imaging research, Beijing, Beijing, China, ²Department of Radiology, University of Washington, ³University of Washington, Vascular Imaging Lab, Seattle, ⁴School of Medicine, Tsinghua University, Center for Biomedical Imaging Research

In this study, we demonstrate a new designed 36-channel neurovascular coil at 3T MRI system. This coil has a high SNR and a wide longitudinal coverage from the top of the head through the upper torso.It is composed of three flexible parts which can be positioned close enough to the surface of the body. High quality images for neurovascular imaging by this coil compared to that of commercial coils are shown here.

Haoqin Zhu¹, Mehran Fallah-Rad¹, Michael Lang¹, Wayne Schellekens¹, Kirk Champagne¹, and Labros Petropoulos^1
1R&D, IMRIS Inc, Winnipeg, MB, Canada

A novel wireless phased array coil that is inductively coupled with the body coil is presented. This coil design eliminates the use of cables and all active components (such as pre-amps and active diodes). This design reduces the overall dimensions of the coils as well as drastically improves the workflow during imaging. Additionally, B1 field sensitivity was improved by 15 dB. SNR and volunteer imaging indicate that the proposed design demonstrate equal performance compared with available 12-channel head coils. Finally, the lack of coil ID requirement enables the coils to work on any OEM MR system at the particular field.

Narayanan Krishanmurthy¹, and Tamer S Ibrahim^1
1University of Pittsburgh, Pittsburgh, PA, United States

In this work we evaluate the effect of a wide variety of receive-only insert geometry including cylinders and helmets with different trace widths on spin excitation field and SAR of a 7T TEM transmit coil.

Ryan Brown¹, Guillaume Madelin¹, Riccardo Lattanzi¹, Gregory Chang¹, Ravinder R Regatte¹, Daniel K Sodickson¹, and Graham C Wiggins^1
1Radiology, New York University School of Medicine, New York, NY, United States

The critical design aim for a dual-tuned sodium/proton coil is to maximize sodium sensitivity and B1+ homogeneity while maintaining adequate proton sensitivity and homogeneity. We explored a nested-coil for sodium/proton imaging at 7T where a stand-alone eight-channel sodium receive array was implemented for high SNR, and a detunable transmit sodium birdcage and four-channel proton transmit-receive array were implemented with minimal disturbance to the sodium array by managing their respective resonances. In vivo sodium SNR was 1.2 to 1.7 times greater in the developed array over a mono-nuclear sodium birdcage coil.

Mark J. van Uden¹, Andor Veltien¹, Barbara H. Janssen¹, and Arend Heerschap^1
1Radiology, Radboud University Nijmegen Medical Centre, Nijmegen, Gelderland, Netherlands

Facioscapulohumeral muscular dystrophy (FSHD) also affects the tibialis anterior in the lower leg of patients. This muscle is ideal to assess the effect of exercise on its bioenergetics by time resolved ³¹P MR spectroscopic imaging. For these experiments optimal SNR is needed. Therefore we present a ¹H/ ³¹P birdcage coil combined with a dedicated 5 channel ³¹P receive array coil to perform 3D ³¹P MRSI on the tibialis anterior. Spectra with excellent SNR of small coils were obtained. The separate elements showed no residual signal outside field of view of a particular element, which demonstrates good element to element decoupling.

Justin G. Pollock¹, Nicola De Zanche², and Ashwin K. Iyer^1
1Dept. of Electrical and Computer Engineering, University of Alberta, Edmonton, Alberta, Canada, ²Oncology, University of Alberta, Edmonton, Alberta, Canada

We demonstrate through simulations that traveling-Wave MRI is possible at lower B0 field strengths by lining the bore with metamaterials having negative permittivity close to zero. The metamaterial liner also dramatically increases spatial uniformity of the transverse fields and leaves ample clear bore for comfortable patient access with minimal additional risk of claustrophobia.

Marcos Alonso Lopez Terrones¹, José Miguel Algarín Guisado¹, Manuel Jose Freire Rosales¹, Felix A. Breuer², and Ricardo Marqués^1
1Electronics and Electromagnetism, University of Seville, Seville, Spain, ²Research Center Magnetic Resonance Bavaria, Würzburg, Germany

The magneto-inductive lens consists of a pair of parallel 2D-arrays of resonators which are inductively coupled between them. This structure has the ability to transfer the magnetic RF field coming from a source (MRI coil) to an imaging plane on the other side of the device. In the present work two receive-only arrays have been built. One array has been combined with the MI-lenses, so that only the main lobe is transferred by the lens but not the side lobes. The MI-lenses improve the SNR in an array without loss of parallel imaging performance compared to a conventional array setup.

Wolfgang Driesel¹, Roland Müller¹, Andreas Schäfer¹, Markus Streicher¹, Carsten Kögler¹, Toralf Mildner¹, and Harald E. Möller^1
1Max Planck Institute for Human Cognitive and Brain Sciences, Leipzig, Germany

At frequencies above 150 MHz, shielded loop coils become impractical because capacitive tuning is no longer possible. The integration of a floating secondary shield allows adaptation of this design to higher magnetic fields. Simulations and initial experiments suggest that a double-shielded dual-loop coil may be used for continuous arterial spin labeling at the human neck at 7 T within legal SAR limits.

Xing Yang¹, Bei Zhang², Ryan Brown², Wonje Lee², and Yudong Zhu^2
1Department of Radiology, Bernard and Irene Schwartz Center for Biomedical Imaging, NYU School of Medicine, New York, NY, United States,²Department of Radiology, Bernard and Irene Schwartz Center for Biomedical Imaging, NYU School of Medicine

The essence of constellation coil transmit and/or receive performance optimization can be described as one of maximizing |B1±|/|E|, quantities that track flip angle-to-SAR ratio (spin excitation) and signal-to-noise ratio (signal detection). It uses an approximately continuous RF structure as well as multiple distributed ports to support generally sophisticated RF current patterns responsible for the ultimate performance with multi-channel transmit and receive1. And the transmit and receive ports’ location are very critical to the ultimate performance. The present study investigated optimum ports' location for multi-nuclear imaging with FDTD simulation

Manushka V. Vaidya^1,2, Daniel K. Sodickson^1,2, Ryan Brown¹, Graham C. Wiggins¹, and Riccardo Lattanzi^1,2
1The Bernard and Irene Schwartz Center for Biomedical Imaging, New York University Langone Medical Center, New York, NY, United States, ²The Sackler Institute of Graduate Biomedical Sciences, New York University School of Medicine, New York, NY, United States

Unanticipated B1 field patterns may be encountered during simulation and experiments, particularly at high operating frequencies. While a distinctive curling of the B1 field is observed at high field strengths, elaborate checkerboard-like patterns may be obtained for certain dielectric samples. In this work, we use full-wave electrodynamic simulations based on dyadic Green’s functions to study the effect of the electrical properties of the sample and main magnetic field strength on the B1 field pattern inside a uniform cylindrical object. We show examples of the curling of the field and interference patterns near resonance, providing a conceptual explanation for each case.

Greig Scott¹, John Pauly², and Pascal Stang^3
1Electrical Engineering, Stanford University, Stanford, California, United States, ²Electrical Engineering, Stanford University, Stanford, United States,³Electrical Engineering, Stanford University

Transmit array systems require remotely sited amplifier racks. We propose a pulse regulator architecture to augment a RF feedback linearizer to enable siting of RF power stages by the magnet while the power supplies can be remote.

Martijn de Greef¹, Ozlem Ipek², Alexander Raaijmakers², Hans Crezee³, and Nico van den Berg^2
1Image Sciences Institute, University Medical Center Utrecht, Utrecht, Utrecht, Netherlands, ²Radiotherapy, University Medical Center Utrecht, Utrecht, Utrecht, Netherlands, ³Radiotherapy, Academic Medical Center, University of Amsterdam, Amsterdam, Noord-Holland, Netherlands

Generic SAR behavior in MRI of the head was studied to evaluate whether patient-specific SAR models which are consuming to construct may be replaced by a generic SAR model. Patient-specific SAR constrained B1+ shimming was performed with generic SAR models. This approach was found to be well suitable for patient-specific B1+ shimming compliant with SAR safety norms at a minimal expense of increased B1+ heterogeneity.

Anna Andreychenko¹, Vincent O. Boer¹, Jan J.W. Lagendijk¹, Peter R. Luijten¹, and Cornelis A.T. van den Berg^1
1Imaging Division, UMC Utrecht, Utrecht, Netherlands

Volume coils are attractive RF transmit systems as they provide a flexible means of RF excitation for the whole body. As an alternative to volume coils a coaxial waveguide concept was proposed recently. Remarkable RF shimming performance of a multi-mode coaxial waveguide was demonstrated for the head at 7T. Here the performance of the multi-mode coaxial waveguide for body torso was investigated in terms of the achieved B1+ efficiency, homogeneity and RF safety constraints. Provided large excitation coverage it was shown that the multi-mode coaxial waveguide could be applied for efficient overall and targeted 3D RF shimming in body torso.

Sebastian Arnold Aussenhofer¹, and Andrew G Webb^1
1Department of Radiology, Leiden University Medical Center, C.J.Gorter Center for High Field MRI, Leiden, Zuid-Holland, Netherlands

A design for a flexible radiative antenna as a high field transmit element is presented, based on high permittivity liquids. This design produces a plane wave in tissue, which simplifies B1 shimming. The flexibility is designed for patient comfort and to work with different body sizes. An array of loop coils is used for signal reception. In vivo results are shown from the ankle of a healthy volunteer.

Yu Li¹, Bing Keong Li¹, Ewald Weber¹, Stuart Crozier¹, Johannes Schneider², Peter Ullmann², and Sven Junge^2
1School of ITEE, The University of Queensland, Brisbane, Queensland, Australia, ²Bruker BioSpin MRI GmbH, Ettlingen, Germany

In this work, the combination of using a 9.4T 8-channel actively detunable small animal transceive volume array with local 2-element receive-only phased array coil is tested. It is shown that with this setup the SNR for small sized rat can be improved.

Stephan Orzada^1,2, Andreas K. Bitz^1,2, Mark E. Ladd^1,2, Kai Nassenstein², and Stefan Maderwald^1
1Erwin L. Hahn Institute for MRI, Essen, NRW, Germany, ²Department of Diagnostic and Interventional Radiology and Neuroradiology, University Hospital Essen, Essen, NRW, Germany

Ultra-high field strengths of 7 T and above promise a high SNR which is useful especially when trying to image nuclei with only a small incidence such as 19F, but inhomogeneities due to the short wavelength cause severe problems. In this work we present a flexible 8ch Tx/Rx coil for human abdominal imaging of 1H and 19F at 7 Tesla allowing the use of the same B1 shim for 1H and 19F. The array and the 8-ch transmit system were successfully tested ex vivo for both 1H and 19F.

Tobias Frauenrath¹, Harald Pfeiffer², Fabian Hezel¹, Matthias Alexander Dieringer¹, Lukas Winter¹, Andreas Graessel¹, Davide Santoro¹, Celal Oezerdem¹, Wolfgang Renz³, Andreas Greiser³, and Thoralf Niendorf^1
1Berlin Ultrahigh Field Facility (B.U.F.F.), Max Delbrueck Center for Molecular Medicine, Berlin, Berlin, Germany, ²Medical Physics and Metrological Information Technology, Physikalisch-Technische Bundesanstalt (PTB), Berlin, Germany, ³Siemens Medical Solutions, Erlangen, Germany

This study transforms the results from 7 T to 3 T, where local transmit coils are helpful to reduce SAR. Shorter TE/TR combination is helpful to gather better image quality at 3 T. For all these reasons, this study was designed to compare the quality of anatomical and functional CMR at 3.0 T under clinical aspects using cardiac optimized transceive coils with a similar receive only coil. Both coils are built similar with four loop structures and compared to a commercial available coil.

Zhentao Zuo^1,2, Joshua Park³, Yanxia Li¹, Zhiguang Li¹, Xinqiang Yan¹, Zihao Zhang^1,2, Yan Zhuo¹, Zang-Hee Cho³, Xiaohong Joe Zhou⁴, and Rong Xue^1
1Key Lab of Brain and Cognitive Science, Beijing MRI Center for Brain Research, Institute of Biophysics, Chinese Academy of Sciences, Beijing, China,²Graduate School, Chinese Academy of Sciences, Beijing, China, ³Neuroscience Research Institute, Gachon University of Medicine and Science, Incheon, Korea, ⁴Depts. of Radiology, Neurosurgery and Bioengineering, Center for MR Research, University of Illinois, Chicago, Illinois, United States

We have constructed an 8-channel phased-array transmit/receive (Tx/Rx) head coil at 7T. The new design gives a larger brain coverage compared to some commercially available 7T RF coils, and provides an unblocked visual field for fMRI experiments. The transmit B1 field uniformity has been improved by linearly adjusting the B1-field phase applied to each of the eight coil elements. Simulations of the local 1g SAR distribution shows that the novel coil can be operated within the IEC regulated limits.Results from the healthy human brain suggest that this coil design is beneficial for structural and functional imaging studies on the anterior temporal and cerebellum regions.

Christoph Leussler¹, Daniel Wirtz¹, Jan Hendrik Wuelbern¹, Peter Vernickel¹, and Peter Forthmann^1
1Philips Research Europe, Hamburg, 22457, Germany

TEM-coils come with a sensitivity profile and field-of view (FOV) that is largely extended in the z-direction compared with birdcage coils (BC). The excess z-FOV leads to safety issues with respect to the specific absorption rate (SAR). We present a novel TEM coil with modified geometry, which has the strip section of each TEM coil element extended laterally at both ends before connecting to the RF screen. Each of these lateral extensions has been found to produce transversal B1 field at the isocenter resulting in a steeper sensitivity profile and thus partially compensating the drawback of a traditional TEM element.

Nikolai I. Avdievich¹, Jullie W. Pan¹, and Hoby H. Hetherington^1
1Neurosurgery, Yale University, New Haven, CT, United States

Decoupling is crucial for constructing transceiver phased arrays. Interaction between the elements can severely compromise both transmission performance and SNR. Previously described decoupling techniques have focused on eliminating the reactance of the mutual impedance, which can limit the obtainable S12 to -10 dB due to residual mutual resistance. Recently we introduced a double-tuned 7T 31P/1H transceiver array. Due to frequency dependence of the mutual inductance two separate decoupling circuits required between each array element. Double-tuning of the decoupling coils can significantly simplify the design. In this work we described a novel inductive decoupling technique, which addresses both these issues.

Tamer S Ibrahim¹, Daniel Stough¹, and Tiejun Zhao^2
1University of Pittsburgh, Pittsburgh, PA, United States, ²Siemens Medical Solutions

In this work, we present the design of a modular transmit head array from sets of coils with highly-coupled elements for 7T head applications. The 20-ch Tx modular array has no distinctive rotation, thus resulting in comparable field coverage in the axial plane and in the z direction. The array has been tested on 15 subjects.

Fabian Hezel¹, Andreas Gräßl¹, Peter Kellman², and Thoralf Niendorf^1,3
1Berlin Ultrahigh Field Facility, MDC Berlin, Berlin, Germany, ²Laboratory of Cardiac Energetics, National Institutes of Health/NHLBI, Bethesda, MD, United States, ³Experimental and Clinical Research Center (ECRC), Charité Campus Buch, Humboldt-University, Berlin, Germany

This study explores the feasibility of large volume coverage abdominal imaging at 7.0 T. It demonstrates the feasibility of ultrahigh resolution GRE imaging, fat/water separated imaging and T2* mapping in a pilot study. For this purpose a novel 32 channel transmit/receive coil is used. Our preliminary results show a in-plane spatial resolution as low as 0.3x0.3 mm so that subtle anatomic details become visible which might be beneficial for advanced clinical applications.

Christakis Constantinides¹, and Stelios Angeli^1
1Mechanical and Manufacturing Engineering, University of Cyprus, Nicosia, Cyprus

 

Sairamesh Raghuraman¹, Frank Resmer², Matthias F Mueller², Michael Manglberger², Stefan Zbyn³, Claudia Kronnerwetter³, Peter Baer⁴, Siegfried Trattnig³, Titus Lanz², and Peter M Jakob^5
1MRB Research Centre, Wuerzburg, Bayern, Germany, ²RAPID Biomedical GmbH, Rimpar, Germany, ³Dept of Radiology, MR Centre - High Field MR, Medical University of Vienna, Austria, ⁴Siemens Healthcare, Munich, Germany, ⁵Dept of Experimental Physics - V, University of Wuerzburg, Germany

High resolution MR imaging of hand is mandatory both to improve early diagnosis and for our understanding of diseases like Rheumatoid Arthritis and Osteoarthritis of wrist and finger joints. While 7 T promises excellent SNR for high resolution imaging of the hand, the usual approach of transmit or transceive arrays may not be the best solutions here, since arrays with a very high density and filling factor are required. This is due to the fact that the hand is a relatively small object and sample noise domination is not necessarily achieved. We present a combination of a volume transmit coil and a 12 channel high density receive (Rx) array for wrist imaging at 7 T.

Volkan Emre Arpinar¹, James S Hyde², and L Tugan Muftuler^1,3
1Department of Neurosurgery, Medical College of Wisconsin, Milwaukee, WI, United States, ²Department of Biophysics, Medical College of Wisconsin, Milwaukee, WI, United States, ³Center for Imaging Research, Medical College of Wisconsin, Milwaukee, WI, United States

The conventional RF coil arrays developed for head imaging usually have poorer sensitivity to the dorsal areas of the brain because the coil elements wrap around the head such that they are more sensitive to anterior, posterior, left and right areas of the brain. In this study, two different end cap designs and a Fo8 element placed on top of the head were investigated using simulations in order to improve SNR in sensorimotor and parietal areas.

Boris Keil¹, James N Blau¹, Philipp Hoecht², Stephan Biber³, Michael Hamm³, and Lawrence L Wald^1,4
1A.A. Martinos Center for Biomedical Imaging, Department of Radiology, Massachusetts General Hospital, Harvard Medical School, Charlestown, MA, United States, ²Siemens, Medical Solutions USA, Charlestown, MA, United States, ³Siemens Healthcare, Erlangen, Germany, ⁴Harvard-MIT Division of Health Sciences and Technology, Cambridge, MA, United States

In brain imaging, parallel acquisition has impacted clinical applications to the point where nearly every brain examination is performed with an array comprising multiple smaller surface coil elements. In this study we design, construct, and evaluate a 64-channel brain array coil and compare it to a 32 channel coil, constructed with the same coil former geometry, in order to precisely isolate the benefit of the two-fold increase in array coil elements We validate the arrays with SNR and g-factor maps and accelerated in vivo imaging.

Andre Kuehne¹, Helmar Waiczies², Enrico Rudorf¹, Frank Seifert¹, and Bernd Ittermann^1
1Physikalisch-Technische Bundesanstalt, Braunschweig & Berlin, Germany, ²Berlin Ultrahigh Field Facility (B.U.F.F.), Max-Delbrueck-Center for Molecular Medicine, Berlin

FDTD simulations are an important tool for any MR coil engineer. The accuracy of the results crucially depends on the sufficient convergence of the simulation. While commercial solvers employ the total system energy content as a convergence measure, we propose to instead monitor the field data at the frequency of interest during the simulation run. This yields a greater insight as to when the desired mode has converged, which for birdcage resonators can be long before the total energy is dissipated. Applying apodization to the time-domain data may significantly speed up the simulation.

Raffi Kalayciyan¹, Friedrich Wetterling¹, Sabine Neudecker², Norbert Gretz², and Lothar R. Schad^1
1Computer Assisted Clinical Medicine, Heidelberg University, Mannheim, Germany, ²Medical Research Center, Heidelberg University, Mannheim, Germany

The quantification of Tissue Sodium Concentration (TSC) requires a homogeneous B1+-field and high SNR to achieve significant values of quantified TSC. Until now, qTSC was performed using long TEs and either by volume resonators, providing high B1+-field homogeneity, but low SNR, or by one transceiver surface coil, which is more sensitive to sodium signal, but suffering from inhomogeneous B1+-field. The aim of this work was to develop a 2-channel 23Na receive-only surface phased-array combined with a commercial double-tuned (23Na/1H) birdcage volume resonator, whereas 3D-UTE sequence with TE<100s[mu] was used.

Ye Li¹, Daniel Vigneron^1,2, and Xiaoliang Zhang^1,2
1Department of Radiology and Biomedical Imaging, University of California San Francisco, San Francisco, CA, United States, ²UCSF/UC Berkeley Joint Graduate Group in Bioengineering, San Francisco, CA, United States

In this work, we investigated the high dielectric insert performance with different field strength in parallel imaging arrays in terms of sensitivity and transmit efficiency for high field MRI applications. We studied the RF electromagnetic field distribution of an 8-channel array with and without the high dielectric insert at 3T, 4T and 7T. Our results show that, B1 fields increase and electric fields decrease with the use of high dielectric inserts at all 3 field strengths but the high dielectric insert provides more benefits at higher fields.

Bei Zhang¹, Daniel K. Sodickson¹, Riccardo Lattanzi¹, and Graham C. Wiggins^1
1The Bernard and Irene Schwartz Center for Biomedical Imaging, NYU Medical Center, New York, New York, United States

In this work, we use simulations and corresponding conceptual arguments to highlight key factors contributing to the presence or absence of asymmetries in RF sensitivity patterns at high field strength. Simple geometrical constructions relating the fields from source currents in coils to the fields from induced eddy or “mirror” currents in conductive samples elucidate the creation of opposite-sense elliptical polarizations in distinct regions of the sample. This framework is used to explain the observed sensitivity pattern of the recently described radiative antenna, and to understand why it differs from that of other common coil types such as loops and striplines.

Riccardo Lattanzi^1,2, Manushka Vaidya^1,2, Graham C Wiggins¹, and Daniel K Sodickson^1,2
1The Bernard and Irene Schwartz Center for Biomedical Imaging, Radiology, New York University Langone Medical Center, New York, NY, United States,²The Sackler Institute of Graduate Biomedical Sciences, New York University School of Medicine, New York, NY, United States

Using an electrodynamic formulation based on a current mode expansion and dyadic Green’s functions, we showed that only 2 divergence-free (i.e. magnetic-type) modes contribute to the ultimate intrinsic SNR (UISNR) in the center of a homogeneous sphere. However, discrete loop coils carry larger noise contributions than the ideal current modes in question, and UISNR cannot therefore be completely achieved with a modest number of loops. At higher field strengths, loops become less and less efficient because noise scales up by a larger factor than the signal. Away from the center, electric-dipole contributions are more significant and loops are increasingly inefficient.

Anna Andreychenko¹, Alexander J.E. Raaijmakers¹, Peter R. Luijten¹, Jan J.W. Lagendijk¹, and Cornelis A.T. van den Berg^1
1Imaging Division, UMC Utrecht, Utrecht, Netherlands

Waveguide slot antennas are popular directional antennas used in microwave engineering at UHF (>300 MHz). The operational RF frequency of ultra high field MRI falls into this frequency range. A slotted coaxial cavity resonator with eight independent ports has been designed for human head imaging at 11.7 T. Based on the FDTD simulations, the resonator showed 13 % higher B1+ efficiency than the conventional birdcage head coil when the quadrature phase settings were applied. The presence of eight ports was exploited for effective RF shimming. This design can be a cheap and easily manufactured alternative to the existing coil designs for ultra high field head MRI.

Xing Yang¹, Ryan Brown¹, Cem Murat Deniz¹, Bei Zhang¹, Wonje Lee¹, Leeor Alon¹, Daniel Sodickson¹, and Yudong Zhu^1
1NYU School of Medicine, New York, NY, United States

MR imaging of nuclei other than proton has been used to investigate metabolism in humans and animals. Additional imaging modalities such as sodium (23Na) MR have the potential to increase the sensitivity and specificity of cancer detection. Currently,dual-tuned coils are required for enhanced multi-nuclear imaging,which are very complicated, and a lot of de-tuned and de-coupled circuits will disturb the performance. The present study demonstrated the feasibility of using a constellation knee coil as transmit and receive coil for 7T multi-nuclear imaging(1H and 23Na) without any de-tuned or de-coupled circuits.