Electronic Poster Session - Engineering
  MR Engineering: Safety & Systems (Non-RF) 2726-2749
  MR Engineering Safety & Systems (Non-RF) 2750-2772
  MR Engineering: RF Coils & Systems 2773-2795
  MR Engineering: RF Coils & Systems 2796-2819

MR Engineering: Safety & Systems (Non-RF)
Click on to view the abstract pdf and click on to view the video presentation. (Not all presentations are available.)
Monday 7 May 2012
Exhibition Hall  10:45 - 11:45

  Computer #  
2726.   1 How to tune a RF-trap?
Ludwig Eberler1, Juergen Nistler1, and Volker Matschl1
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.

2727.   2 Remotely measuring induced radiofrequency currents on wires in MRI
Greg Hungtingdon Griffin1, Kevan J Anderson2, and Graham A Wright1,2
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.

2728.   3 Implant MR Imaging Adverse Event Analysis Report ¨C FDA MAUDE Database Study
Yuan Ma1, Gaohong Wu1, Wei Sun1, Joe Schaefer1, Roee Lazebnik1, and Glen Sabin1
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.

2729.   4 On the Complete Analysis of Lenz’s Effect on the Artificial Heart Valves during Magnetic Resonance Imaging
Laleh Golestanirad1,2, Graham Wright1, and Simon Graham1
1Medical Biophysics, University of Toronto, Toronto, Ontario, Canada, 2Laboratory of Electromagnetics and Acoustics (LEMA), Ecole Polytechnique Federale de Lausanne, Lausanne, Switzerland


2730.   5 Heating near Deep Brain Stimulation (DBS) Lead Electrodes during Imaging with a 3T Transceive Head Coil in Cadaveric Porcine Heads
Devashish Shrivastava1, Timothy Hanson2, Ute Goerke1, Lance DelaBarre1, Rachana Visaria3, Paul Iaizzo1, Aviva Abosch1, and JT Vaughan1
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.

2731.   6 MR Safety Standards for Medical Students Nationwide
Elizabeth Hipp1, Steffen Sammet1, and Christopher Straus1
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.

2732.   7 Practical approaches to ensure we do not exceed a non-standard SAR level
Jonathan Ashmore1,2, Gareth Barker3, Ruth O'Gorman4, and Geoff Charles-Edwards5
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.

2733.   8 In vivo B1-based SAR determination in a multi-transmit system with DREAM
Ulrich Katscher1, Kay Nehrke1, Hanno Homann1, and Peter Börnert1
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.

2734.   9 Estimation of electric field maps from B1+ and transceive phase measurements for local SAR evaluation
Alessandro Sbrizzi1, Hans Hoogduin2, Jan J Lagendijk2, Peter R Luijten2, and Cornelis A van den Berg3
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.

2735.   10 GPU-accelerated SAR computation with arbitrary averaging shapes
Andre Kuehne1, Frank Seifert1, and Bernd Ittermann1
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.

2736.   11 RF Coil Local Power Deposition and Efficiency Evaluation Using a Phantom with High Sensitivity to Temperature Change
Leeor Alon1,2, Assf Tal1, Cem Murat Deniz1,2, Gene Young Cho1,2, Daniel Sodickson1,2, and Yudong Zhu1,2
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.

2737.   12 SAR and SNR comparison for infants between adult head and knee MRI coils
Zhangwei Wang1, Owen Arthurs2, Desmond T.B. Yeo3, Gemma R Cook2, and Fraser J Robb1
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.

13 Improving SNR in high b-value diffusion imaging using Gmax = 300 mT/m human gradients
M. Dylan Tisdall1,2, Thomas Witzel1, Veneta Tountcheva1,2, Jennifer A. McNab1,2, Julien Cohen-Adad1,2, Ralph Kimmlingen3, Philipp Hoecht4, Eva Eberlein3, Keith Heberlein4, Franz Schmitt3, Herbert Thein3, Van J. Wedeen1,2, Bruce R. Rosen1,2, and Lawrence L. Wald1,2
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.

2739.   14 Should minimax|j| wire spreading be used for whole body gradient coils?
Michael S Poole1, Hector Sanchez Lopez1, and Stuart Crozier1
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.

2740.   15 Feasibility of 2G HTS (YBCO) Roebel cable MRI gradient coils
Robert Slade1, Zhenan Jiang2, and A D Caplin3
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.

2741.   16 An optimal central gap size for the split gradient coil design
Limei Liu1, Hector Sanchez Lopez1, Michael Poole1, Feng Liu1, and Stuart Crozier1
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.

2742.   17 3D Magnetic Particle Imaging with a Traveling Wave
Patrick Vogel1,2, Martin A. Rückert1,2, Peter Klauer1,2, Walter H. Kullmann2, Peter M. Jakob1,3, and Volker C. Behr1
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.

2743.   18 Simultaneous MR and Optical Imaging of Tumor Microenvironment
Mir Farrokh Salek1, and Arthur Gmitro1
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.

2744.   19 A landmark-free MRI scanner concept
Ileana Hancu1, Keith Park1, and Robert Darrow1
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.

2745.   20 A 72-channel whole-head system for combined ultra-low-field MRI and magnetoencephalography
Panu T. Vesanen1, Jaakko O. Nieminen1, Koos C.J. Zevenhoven1, Juhani Dabek1, Juho Luomahaara2, Juha Hassel2, Jari Penttilä3, Andrey V. Zhdanov1, Fa-Hsuan Lin1,4, Yi-Cheng Hsu1,5, Lauri T. Parkkonen6, Juha Simola6, Antti I. Ahonen6, and Risto J. Ilmoniemi1
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.

2746.   21 Design of a Local Shim Coil to Improve B0 Homogeneity in the Cervical Spine Region
Stephan Biber1, Katrin Wohlfarth1, John Kirsch1, and Andreas Schmidt1
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.

22 Improvements in magnetic shielding of a B0 insert coil
Chad Tyler Harris1, William B Handler1, Brian Dalrymple1, Frank Van Sas1, Yonathan Araya2, Timothy J Scholl2,3, and Blaine A Chronik1,3
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.

2748.   23 Effect of Superconducting Components on Imaging Field Homogeneity in Ultra-Low-Field MRI
Andrey Zhdanov1, Jaakko O. Nieminen1, Panu T. Vesanen1, Koos C.J. Zevenhoven1, Juhani Dabek1, Juho Luomahaara2, Juha Simola3, Antti I. Ahonen3, and Risto J. Ilmoniemi1
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.

2749.   24 Wireless Magnetic Field Monitoring
Matthew J. Riffe1, Daniel Neumann2, Colin Blumenthal3, Gregory Lee4, Nicole Seiberlich1, and Mark A. Griswold1,4
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.
Electronic Poster Session - Engineering

MR Engineering Safety & Systems (Non-RF)
Click on to view the abstract pdf and click on to view the video presentation. (Not all presentations are available.)
Monday 7 May 2012
Exhibition Hall  11:45 - 12:45

  Computer #  
2750.   1 Designing shim coils with minimax|j|
Michael S Poole1, Hector Sanchez Lopez1, and Stuart Crozier1
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.

2751.   2 Efficient hybrid eddy current simulation in thick cylinders and thin surfaces of arbitrary geometry induced by MRI gradient coils.
Hector Sanchez-Lopez1, Michael Poole1, Ewald Weber1, Limei Liu1, and Stuart Crozier1
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.

2752.   3 A method for designing gradient coils with minimum maximum temperature: theoretical considerations
Peter T. While1, Michael Poole2, Larry K. Forbes1, and Stuart Crozier2
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.

2753.   4 Design Optimizations Regarding Eddy Currents of a High Performance Head Gradient Coil
Silke M. Lechner-Greite1, Jean-Baptiste Mathieu2, Seung-Kyun Lee3, Bruce C. Amm4, Thomas K. Foo5, John F. Schenck6, Matt A. Bernstein7, and John Huston7
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.

5 Simultaneous Whole-Body PET/MRI with Continuous Table Motion
Harald Braun1, Susanne Ziegler1, Daniel H Paulus1, Jens U Krause1, and Harald H Quick1
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.

6 MR-guided Radiotracer Input Function Estimation in Simultaneous MR/PET
Daniel Burje Chonde1,2, and Ciprian Catana1
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.

2756.   7 Simultaneous Whole-Body PET/MR: Challenges and Opportunities
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 Schwaiger1
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.

2757.   8 New generation hybrid FMT/MRI system used to assess lower case Greek beta-amyloid plaque load on APP23 mice in vivo
Katerina Dikaiou1, Florian Stuker1, Jan Klohs1, Andreas Elmer1, Jorge Ripoll1,2, and Markus Rudin1,3
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.

2758.   9 Evaluation of conventional MR surface coil impact on PET quantification
Hua-Lei Zhang1, Sebastian Fürst1, Axel Martinez-Möller1, Isabel Dregely1, Alexandra Bartel1, Markus Schwaiger1, and Stephan Nekolla1
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.

2759.   10 Simulation and experimental verification of eddy current due to RF coil shielding
Yujuan Zhao1, Tiejun Zhao2, Daniel Stough1, Chad Harris3, William Handler3, Hai Zheng1, Shaohua Lin4, Fernando Boada1, Blaine Chronik3, and Tamer Ibrahim1
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.

2760.   11 Toward an integrated RF-shield-gradient coil design method
Hector Sanchez-Lopez1, Ewald Weber1, Michael Poole1, Limei Liu1, and Stuart Crozier1
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.

2761.   12 Novel Method to Measure and Characterize Shim Induced Eddy Current Fields with Calibration Applications for Dynamic Shim Updating at 7T
Alex A Bhogal1, Jos Koonen2, Jeroen Siero3, Vincent Boer3, Dennis Klomp3, Peter Luijten3, and Hans Hoogduin3
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.

2762.   13 MRI-induced Vibrations in Active Implantable Medical Devices: Effect on the Device
Ramez E. N. Shehada1, Rohan More1, Reza Imani1, Wudi Zhou1, Micah Meulmester1, Benjamin Coppola1, Jon Dietrich1, Richard Williamson1, and Ali Dianaty1
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.

2763.   14 MRI Safety Hazard from Undetected Metal Thread in Clothing
Mark C Oswood1,2
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.

2764.   15 MR Imaging of Patients with Stents is Safe at 7.0 Tesla
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 Klomp2
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.

2765.   16 A guide to improving and testing the MR compatibility of external devices
Julian Maclaren1, Michael Herbst1, and Maxim Zaitsev1
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.

2766.   17 Simulation study on safety of dental implants at 7T
Joep Wezel1,2, Wyger Brink1, Bert Jan Kooij2, and Andrew Webb1
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.

2767.   18 RF Safety of Aneurysm Clips at 7 Tesla: Effect of Field Polarization
Yacine Noureddine1,2, Oliver Kraff2,3, Mark E. Ladd2,3, Gregor Schaefers1, Karsten H. Wrede4, and Andreas K. Bitz2,3
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.

2768.   19 What peak power do I need from my amplifiers for multi-transmit?
Daniel James Lee1, and Paul M Glover1
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.

2769.   20 Thermal simulations in the human head for high field MRI using parallel transmission
Aurélien MASSIRE1, Martijn CLOOS1,2, Michel LUONG2, Alexis AMADON1, Alexandre VIGNAUD3, Christopher J. WIGGINS1, Denis LE BIHAN1, and Nicolas BOULANT1
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.

2770.   21 Local SAR Control for Parallel Transmit MRI using Multiple Patient Models
Hanno Homann1, Inagmar Graesslin1, Ulrich Katscher1, Peter Vernickel1, Kay Nehrke1, and Peter Börnert1
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.

2771.   22 SAR Comparison for "Head First" and "Feet First" Patient Loading at 3T MRI with Numerical Simulations
Xin Chen1, Yong Wu2, Zhen Yao2, Michael Steckner1, and Robert Brown2
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.

2772.   23 Difficulties Associated with Aligning Simulated and Constructed Coils
Leeor Alon1,2, Cem Murat Deniz1,2, Ryan Brown1, Daniel Sodickson1,2, and Yudong Zhu1,2
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.

Electronic Poster Session - Engineering

MR Engineering: RF Coils & Systems
Click on to view the abstract pdf and click on to view the video presentation. (Not all presentations are available.)
Monday 7 May 2012
Exhibition Hall  10:45 - 11:45

  Computer #  
2773.   25 Lessons Learned in Applying Efficient B1 Shimming Techniques at UHF
Daniel K. Stough1, and Tamer Ibrahim2
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.

2774.   26 Inverse Field-based Approach for the Evaluation of Electromagnetic Fields and its Application in Local SNR Shimming
Jin Jin1, Feng Liu1, Ewald Weber1, and Stuart Crozier1
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.

2775.   27 Optimization and sensitivity analysis of Capacitive Inductive and Transformer decoupling schemes for RF coil arrays
Volkan Emre Arpinar1, and L Tugan Muftuler1,2
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.

2776.   28 Simulation of Targeted RF-Heating at 1.5T, 3.0T, 7.0T, 9.4T and 11.7T MR
Lukas Winter1, Celal Özerdem1, Helmar Waiczies1, and Thoralf Niendorf1,2
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.

2777.   29 Efficient and comprehensive EM field simulation procedure for pTX experiments
Frank Seifert1, Tomasz Lindel1, and Peter Ullmann2
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.

2778.   30 Feasibility study of a multi-channel pTX-array bodycoil with tray-shielding
Volker Matschl1, Juergen Nistler1, and Sandra Weiss2
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.

2779.   31 Field shaping arrays: a means to address shading in high field breast MRI
Ileana Hancu1, Seung-Kyun Lee1, W. Thomas Dixon1, Laura Sacolick2, Ricardo Becerra3, Zhenghui Zhang3, Graeme McKinnon3, and Vijayanand Alagappan4
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.

2780.   32 Linear phase non-resonant hybrid lumped element / twisted microstrip RF transmit coil
Rock Hadley1, Jim Stack2, John Roberts3, Robb Merrill3, Dennis Parker3, and Glen Morrell3
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.

2781.   33 Optimizing TEM Transceiver Elements at 7 Tesla
Can Akgun1, Lance DelaBarre2, Carl Snyder2, Kamil Ugurbil2, Anand Gopinath3, and John Thomas Vaughan2
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.

2782.   34 7T External Prostate Array with Single Channel Transmit: Simulation and Experiment
Bei Zhang1, Andrew B Rosenkrantz2, Daniel K. Sodickson1, Samir S Taneja2, Cornel Stefanescu1, and Graham C Wiggins1
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.

2783.   35 Combining cylindrically mounted dipoles with loops on a transverse plane for better head coverage in parallel transmission.
Christopher John Wiggins1, Marie-France Hang1, Alexis Amadon1, Martijn Cloos1, Nicolas Boulant1, Michel Luong2, Guillaume Ferrand2, and Karl Edler1
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.

2784.   36 A Variable Power Combiner for 7 Tesla MRI system with 16-channel coil array
Pedrm Yazdanbakhsh1, Klaus Solbach1, Andreas K Bitz2, and Mark E Ladd2
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.

2785.   37 An Inexpensive Implementation of a Scalable MR Receiver with Digital Optical Transmission
Weinan Tang1, Hongyu Sun1, Zechong Xiong1, and Weimin Wang1
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.

2786.   38 A 32-channel head coil array with circularly symmetric geometry for 2D accelerated 3D human brain imaging
Ying-Hua Chu1, Boris Keil2, Wei-Chao Chen3, Wen-Jui Kuo4, Fa-Hsuan Lin1,2, and Fa-Hsuan Lin5
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.

2787.   39 A New Designed 36-Channel Neurovascular Coil at 3T
xinyuan wang1, Rui Li1, Cecil Hayes2, Niranjan Balu3, Xihai Zhao4, and Chun Yuan2
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.

2788.   40 A novel multichannel wireless receive phased array coil without integrated preamplifiers for high field MR imaging applications
Haoqin Zhu1, Mehran Fallah-Rad1, Michael Lang1, Wayne Schellekens1, Kirk Champagne1, and Labros Petropoulos1
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.

2789.   41 Receiver-Only Array Geometry and Design influence on B1+ Field and Specific Absorption Rate (SAR)
Narayanan Krishanmurthy1, and Tamer S Ibrahim1
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.

2790.   42 Design of a Nested Sodium and Proton Array for 7 Tesla Knee Imaging
Ryan Brown1, Guillaume Madelin1, Riccardo Lattanzi1, Gregory Chang1, Ravinder R Regatte1, Daniel K Sodickson1, and Graham C Wiggins1
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.

2791.   43 1H/ 31P birdcage coil combined with dedicated multi-element 31P receive coil for optimal 31P MRSI of the tibialis anterior
Mark J. van Uden1, Andor Veltien1, Barbara H. Janssen1, and Arend Heerschap1
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.

2792.   44 Traveling-Wave MRI at Lower B0 Field Strengths Using Metamaterial Liners
Justin G. Pollock1, Nicola De Zanche2, and Ashwin K. Iyer1
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.

2793.   45 Application of Magneto-Inductive Metamaterial Lenses in Parallel Imaging
Marcos Alonso Lopez Terrones1, José Miguel Algarín Guisado1, Manuel Jose Freire Rosales1, Felix A. Breuer2, and Ricardo Marqués1
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.

2794.   46 A Double-Shielded Label Coil for Continuous Arterial Spin Labeling at 7 T
Wolfgang Driesel1, Roland Müller1, Andreas Schäfer1, Markus Streicher1, Carsten Kögler1, Toralf Mildner1, and Harald E. Möller1
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.

2795.   47 Investigation optimum ports' location for multi-nuclear constellation coil
Xing Yang1, Bei Zhang2, Ryan Brown2, Wonje Lee2, and Yudong Zhu2
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
Electronic Poster Session - Engineering

MR Engineering: RF Coils & Systems
Click on to view the abstract pdf and click on to view the video presentation. (Not all presentations are available.)
Monday 7 May 2012
Exhibition Hall  11:45 - 12:45

  Computer #  
2796.   25 B1+ and B1- field pattern dependence on the electrical properties of the sample and the static magnetic field strength
Manushka V. Vaidya1,2, Daniel K. Sodickson1,2, Ryan Brown1, Graham C. Wiggins1, and Riccardo Lattanzi1,2
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.

2797.   26 Pulsed Power Regulated Tx Array Amplifier Architecture
Greig Scott1, John Pauly2, and Pascal Stang3
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.

2798.   27 A practically feasible approach to SAR-constrained patient-specific B1+ shimming in 7T head imaging based on generic SAR behavior.
Martijn de Greef1, Ozlem Ipek2, Alexander Raaijmakers2, Hans Crezee3, and Nico van den Berg2
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.

28 RF shimming in human torso with the multi-mode coaxial waveguide at 7T
Anna Andreychenko1, Vincent O. Boer1, Jan J.W. Lagendijk1, Peter R. Luijten1, and Cornelis A.T. van den Berg1
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.

2800.   29 Flexible Radiative Antennas as transmit elements for high field MRI
Sebastian Arnold Aussenhofer1, and Andrew G Webb1
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.

2801.   30 Pre-clinical imaging at 9.4T using a versatile 8-channel Transceive Array
Yu Li1, Bing Keong Li1, Ewald Weber1, Stuart Crozier1, Johannes Schneider2, Peter Ullmann2, and Sven Junge2
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.

2802.   31 An 8-channel dual-tuned 1H/19F flexible 7 Tesla body coil with meanders
Stephan Orzada1,2, Andreas K. Bitz1,2, Mark E. Ladd1,2, Kai Nassenstein2, and Stefan Maderwald1
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.

2803.   32 Lessons Learned from Cardiac MRI at 7.0 T: LV Function Assessment at 3.0 T Using Local Multi-Channel Transceiver Coil Arrays
Tobias Frauenrath1, Harald Pfeiffer2, Fabian Hezel1, Matthias Alexander Dieringer1, Lukas Winter1, Andreas Graessel1, Davide Santoro1, Celal Oezerdem1, Wolfgang Renz3, Andreas Greiser3, and Thoralf Niendorf1
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.

2804.   33 An Elliptical Octagonal Phased-Array Head Coil for Multi-Channel Transmission and Reception at 7T
Zhentao Zuo1,2, Joshua Park3, Yanxia Li1, Zhiguang Li1, Xinqiang Yan1, Zihao Zhang1,2, Yan Zhuo1, Zang-Hee Cho3, Xiaohong Joe Zhou4, and Rong Xue1
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.

2805.   34 U-shaped Ladder TEM-Coil Structure with Truncated Sensitivity Profile in z-Direction for High Field MRI
Christoph Leussler1, Daniel Wirtz1, Jan Hendrik Wuelbern1, Peter Vernickel1, and Peter Forthmann1
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.

2806.   35 Novel Inductive Decoupling for Single- and Double-Tuned Transceiver Phased Arrays to Compensate for both Reactive and Resistive Components of the Mutual Impedance.
Nikolai I. Avdievich1, Jullie W. Pan1, and Hoby H. Hetherington1
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.

2807.   36 20-Ch Tx Modular Array for 7T PTX Applications
Tamer S Ibrahim1, Daniel Stough1, and Tiejun Zhao2
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.

2808.   37 Feasibility of Abdominal MRI at 7.0 T Using a Novel 32 Channel Transceiver Coil Array
Fabian Hezel1, Andreas Gräßl1, Peter Kellman2, and Thoralf Niendorf1,3
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.

2809.   38 Minimizing Mutual Inductance in NMR Phased Arrays: The Paddle End-Ring Design Revisited
Christakis Constantinides1, and Stelios Angeli1
1Mechanical and Manufacturing Engineering, University of Cyprus, Nicosia, Cyprus


2810.   39 A volume coil and a multichannel receive array for high resolution hand/wrist imaging at 7 T
Sairamesh Raghuraman1, Frank Resmer2, Matthias F Mueller2, Michael Manglberger2, Stefan Zbyn3, Claudia Kronnerwetter3, Peter Baer4, Siegfried Trattnig3, Titus Lanz2, and Peter M Jakob5
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.

2811.   40 Novel RF coil array designs to improve SNR in dorsal areas of the brain
Volkan Emre Arpinar1, James S Hyde2, and L Tugan Muftuler1,3
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.

2812.   41 A 64-Channel Brain Array Coil for 3T Imaging
Boris Keil1, James N Blau1, Philipp Hoecht2, Stephan Biber3, Michael Hamm3, and Lawrence L Wald1,4
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.

2813.   42 Reliable FDTD simulation convergence detection and acceleration
Andre Kuehne1, Helmar Waiczies2, Enrico Rudorf1, Frank Seifert1, and Bernd Ittermann1
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.

2814.   43 Bilateral kidney 23Na-MRI: quantification of tissue sodium concentration by using a two-element phased array system with homogeneous B1-field excitation and ultra-short TE
Raffi Kalayciyan1, Friedrich Wetterling1, Sabine Neudecker2, Norbert Gretz2, and Lothar R. Schad1
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.

2815.   44 Investigation of field dependence of high dielectric insert properties in parallel imaging arrays
Ye Li1, Daniel Vigneron1,2, and Xiaoliang Zhang1,2
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.

2816.   45 Why Does the Radiative Antenna Have no B1 Twisting at 7T? Framework for and Applications of a Conceptual “Mirror Current” Model of Coil-Tissue Interactions
Bei Zhang1, Daniel K. Sodickson1, Riccardo Lattanzi1, and Graham C. Wiggins1
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.

2817.   46 The underlying cause of the increasing performance gap between loop arrays and the ultimate SNR with increasing field strength
Riccardo Lattanzi1,2, Manushka Vaidya1,2, Graham C Wiggins1, and Daniel K Sodickson1,2
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.

2818.   47 Slotted coaxial cavity resonator for head imaging at ultra high fields
Anna Andreychenko1, Alexander J.E. Raaijmakers1, Peter R. Luijten1, Jan J.W. Lagendijk1, and Cornelis A.T. van den Berg1
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.

2819.   48 Constellation Coil for Multi-nuclear Imaging
Xing Yang1, Ryan Brown1, Cem Murat Deniz1, Bei Zhang1, Wonje Lee1, Leeor Alon1, Daniel Sodickson1, and Yudong Zhu1
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.