Joint Annual Meeting ISMRM-ESMRMB 2014 10-16 May 2014 Milan, Italy



4866-4887 MR Safety & RF Arrays
4888-4910 RF Safety

MR Safety & RF Arrays

Thursday 15 May 2014
Exhibition Hall  13:30 - 14:30

  Computer #  
49 Worst-Case Analysis of RF-Induced Heating During MRI Scanning in a Generic Multi-Component Orthopedic Medical Implant Applying the Design of Experiment Method (DoE)
Mahdi Abbasi1,2, Gregor Schaefers1, Juan D. Sánchez1, and Daniel Erni2
1MR:comp GmbH, Gelsenkirchen, NRW, Germany, 2General and Theoretical Electrical Engineering (ATE), University of Duisburg-Essen, Duisburg, NRW, Germany

MRI is known as a non-invasive imaging technique of the inner parts of the body. Temperature rise in surrounding tissue of a metallic implant needs to be calculated carefully for the patient’s safety. Calculating spatial induced electric field and SAR become more complex when the implant is non-uniform in shape and contains several parts. The effect of each component of a multi-component generic hip implant on RF heating has been studied by applying the Design of Experience (DoE) method. By using Taguchi method, the effect of each variable could be estimated as well as any arbitrary configuration of the implant including worst and safest configurations.

4867.   50 Evaluation of Multi-Section Resistive Tapered Stripline (RTS) Lead Wires to Reduce SAR Near Implanted DBS Electrodes During MRI
Peter Serano1,2, Leonardo M. Angelone3, and Giorgio Bonmassar1
1Athinoula A. Martinos Center for Biomedical Imaging, Charlestown, MA, United States, 2Electrical and Computer Engineering, University of Maryland, College Park, MD, United States, 3U.S. Food and Drug Administration CDRH/OSEL/DP, Silver Spring, MD, United States

When performing MRI in patients with DBS implants, one of the major issues is the heating of tissue surrounding the implant due to radiofrequency (RF) pickup of the implant acting as an antenna. We present an extensive evaluation of the design parameters of a novel DBS lead for MRI based on Resistive Tapered Stripline (RTS) technology. Our results show this innovative high scattering technology can allow for up to a 40% decrease in tissue specific absorption rate (SAR) near the DBS electrode while maintaining low lead resistivity for continuous current injection.

4868.   51 SAR reduction in deep brain stimulation patients using parallel transmission
Bastien Guerin1, Sara Sprinkhuizen1, Cristen LaPierre1,2, Yigitcan Eryaman1,3, and Lawrence L Wald1,4
1A. A. Martinos Center for Biomedical Imaging, Dpt. of Radiology, Massachusetts General Hospital, Charlestown, MA, United States, 2Dpt. of Physics, Harvard Univerity, Cambridge, MA, United States, 3Madrid-MIT M+Vision Consortium in RLE, Massachusetts Institute of Technology, Cambridge, MA, United States, 4Division of Health Sciences Technology, Harvard-MIT, Cambridge, MA, United States

Deep brain stimulation (DBS) is used to treat Parkinson disease, essential tremor and depression. DBS involves implanting electrodes permanently in the patient’s brain. When placed inside an MRI scanner the DBS lead heats up because of strong coupling with the RF field, which is dangerous to the patient. We show in simulations and phantom experiments that parallel transmission can excite the MRI signal without creating significant SAR at the tip of the DBS lead by minimizing the electric field along the DBS lead wire. Application of this approach in vivo could elucidate the mechanisms of action of DBS.

4869.   52 Measuring RF currents induced in implants using B1+ maps
Mélina Bouldi1 and Jan M. Warnking1,2
1Grenoble Institut des Neurosciences - UJF, Grenoble, Rhônes Alpes, France, 2Inserm U836, Grenoble, Rhônes Alpes, France

In the presence of conductive implants, the B1+ field presents distortions generated by induced RF currents, which can be linked to the expected SAR. We fitted a theoretical model of the induced B1+ distortions to experimental B1 data obtained in an ASTM phantom to measure the current in a conducting wire. This indirect measurement of wire current was compared to EM simulations in a numerical model. This work may lead to methods allowing rapid evaluation of the RF safety of conductive wire in a given configuration.

4870.   53 Subjective Assessment of Sensations Experienced by 7 Tesla Magnetic Resonance Imaging -permission withheld
Ikuko Uwano1, Tsuyoshi Metoki1, Fusako Sendai1, Ryoko Yoshida1, Kohsuke Kudo1,2, Fumio Yamashita1, Satomi Higuchi1, Kenji Ito1, Jonathan Goodwin1,2, Taisuke Harada1,2, and Makoto Sasaki1
1Division of Ultrahigh Field MRI, Institute for Biomedical Sciences, Iwate Medical University, Yahaba, Iwate, Japan, 2Department of Diagnostic and Interventional Radiology, Hokkaido University Hospital, Sapporo, Hokkaido, Japan

We investigated the unpleasant sensations experienced by large number of the Japanese subjects during MRI examination using a 7T scanner that has a slow table-feed speed, and then compared these sensations to the previous reports. Unpleasant sensations such as vertigo were experienced at 7T especially when the table is moving, but were infrequent and weak when compared with the previous studies presumably do to the slow table-feed speed, indicating that the degree of subjective discomforts at 7T is tolerable and may be acceptable in the usage of the clinical practice in the future.

4871.   54 MRI Gradient Field-Induced Heating and its Frequency Dependency for Different Materials
Juan D. Sánchez1, Mahdi Abbasi1, Amin Douiri2, Morwan Choli3, Wolfgang Goertz2, and Gregor Schaefers3
1Dept. of Numerical Simulation, MR:comp GmbH, Gelsenkirchen, NRW, Germany, 2Test Laboratory, MR:comp GmbH, Gelsenkirchen, NRW, Germany,3Dept. of Consulting, MR:comp GmbH, Gelsenkirchen, NRW, Germany

This study evaluated the gradient-induced heating of a pair of metallic plates (dimensions similar to commercial medical implantable pulse generators IPGs) made of different materials in order to determine a suitable test procedure for the test of gradient induced heating. From the obtained results, it is observed that a worst-case exposure cannot be concluded only by a particular set of gradient field conditions for all different implants.

4872.   55 Torque and Translational force Considerations for ferromagnetic shells in MR Imaging
Vahid Ghodrati1 and Abbas N Moghaddam1,2
1BME, Tehran Polytechnic, Tehran, Tehran, Iran, 2School of Cognitive Sciences, Institute for Studies in Theoretical Physics and Mathematics, Tehran, Iran

In some injuries, such as those happen in the battle field, part of shells or foreign objects that may include magnetic materials remain in victim’s body. In this research we calculate the torque and translational force for specific ferromagnetic objects. Translational force reaches its maximum value near the opening to the bore. Near the isocenter, however, there is no translational force acting on the ferromagnetic spherical object. For a long cylindrical shell, such as a niddle, or for a flat cylindrical shell, like a disk, the torque inside the bore is quite significant. Torque can be managed by a prior knowledge about the object orientation from an auxiliary imaging modality.

4873.   56 MRI Safety and Cardiac Pacemakers/ICDs
Karl K. Vigen1, Kurt S. Hoffmayer2, and Scott B. Reeder1,3
1Radiology, University of Wisconsin-Madison, Madison, WI, United States, 2Medicine, University of Wisconsin-Madison, Madison, WI, United States,3Medicine, Medical Physics and Biomedical Engineering, University of Wisconsin-Madison, WI, United States

Cardiac pacemakers and implantable cardioverter defribrillators (ICDs) have been traditionally been contraindicated for MRI. Recently, device manufacturers have developed pacemakers and ICDs that are specifically designed and approved as MRI-compatible. In addition, several sites have reported successfully imaging patients with conventional pacemakers and ICDs, and a large clinical trial is underway which is investigating the use of MRI for patients with conventional devices.

4874.   57 Perfluorocarbon Lung Clearance Evaluated with Dual-Nuclei 19F and 1H MRI in the Context of Total Liquid Ventilation
Ludovic de Rochefort1, Mourad Chenoune2, Anis Ben Yahmed1, Charlotte Alibert1, Jérémy Pépin1, Fanny Lidouren2, Lys Darbera2, Alain Berdeaux2, Matthias Korn1, Rose-Marie Dubuisson1, Luc Darrasse1, Daniel Isabey3, and Renaud Tissier2
1IR4M, Univ. Paris-Sud, CNRS, UMR 8081, Orsay, France, 2Inserm UMR 955-3, Univ Paris Est, Ecole Nationale Vétérinaire de Maisons-Alfort, Maisons-Alfort, France, 3Inserm UMR 955-13, Univ Paris Est, Créteil, France

Fast hypothermia induced by Total Liquid Ventilation (TLV) with Perfluorocarbons (PFC) has been shown to be cardioprotective. TLV procedure includes a lung filling phase, the ventilation, and a final clearance during which PFCs are eliminated from the lungs. For the potential clinical transfer, it is important to select PFCs that are better tolerated, as the clearance phase may vary with the PFC physical properties. Here, we present the evaluation of the clearance from pig lungs for three different liquid PFCs with a quantitative dual-nuclei (1H, 19F) MRI protocol at 1.5 T providing insights for selecting PFCs for human use

4875.   58 Gd-enhanced MRI after therapeutic ferumoxytol for iron deficiency anemia - An in-vitro study for optimal contrast timing and dose determination.
Sandeep Arora1, Judy Yee1, David Saloner1, Rizwan Aslam1, and Thomas Hope1
1Radiology and Biomedical Imaging, University of California, San Francisco, San Francisco, California, United States

Therapeutic ferumoxytol injections can confound subsequently performed magnetic resonance imaging using gadolinium based contrast agents due to its superparamagnetic effects. In this in vitro study, we image various concentrations of ferumoxytol and gadolinium to determine concentration of ferumoxytol which will not affect arterial enhancement in subsequent contrast enhanced scans. Our images demonstrate that significant enhancement can be seen after single dose gadolinium enhanced scans two half-lives with initial ferumoxytol concentration being 300 microgram/ml. Even after one half-life, significant enhancement can be seen with double or triple dosing of gadolinium based contrast agents.

4876.   59 RF Heating of Gold Cup and Conductive Plastic Electrodes during Simultaneous MRI and EEG
Mukund Balasubramanian1, William M. Wells2, John R. Ives3, Patrick Britz4, Tobias Loddenkemper5, Padmavathi Sundaram1, Robert V. Mulkern1, and Darren B. Orbach1
1Department of Radiology, Boston Children's Hospital, Boston, Massachusetts, United States, 2Department of Radiology, Brigham and Women's Hospital, Boston, Massachusetts, United States, 3Ives EEG Solutions, Inc., Newburyport, Massachusetts, United States, 4Brain Products GmbH, Gilching, Germany, 5Department of Neurology, Boston Children's Hospital, Boston, Massachusetts, United States

The EEG electrodes used in clinical settings are typically removed prior to MRI scanning at 3T due to RF heating concerns. Since it would be advantageous to leave these electrodes on during routine clinical scans and to record from them during functional MRI scans, we measured the temperature changes under two types of clinical electrodes during a variety of 3T MRI scans, using watermelons as phantoms. Our results suggest that these electrodes could be used safely at 3T, as long as the EEG wire lengths and the SAR of the MRI sequences are both carefully taken into consideration.

4877.   60 Magnetic Forces on Medical Implants
Robert J. Deissler1, Michael Martens1, Tanvir Baig1, Zhen Yao1, Charles Poole1, and Robert Brown1
1Department of Physics, Case Western Reserve University, Cleveland, Ohio, United States

Medical implants raise important safety concerns for patients receiving MRI due to the forces and torques acting on the implants during patient scanning or entry. The implant can be deemed MRI safe if the magnetic forces and torques are less than the forces due to gravity. Using a representative contour plot of B|grad B| for a 1.5 T magnet design we determine safe zones which also depend on the material susceptibility. We show that if the implant is deemed safe for static forces it will also be safe for static torques.

4878.   61 Heating of bilateral hip prostheses in a human body model induced by a multi-axis gradient coil set
Hector Sanchez-Lopez1, Luca Zilberti2, Oriano Bottauscio2, Jeffrey Hand3,4, Annie Papadaki5, Fangfang Tang1, Mario Chiampi6, and Stuart Crozier1
1School of Information Technology & electrical Engineering, The University of Queensland, Brisbane, QLD, Australia, 2Istituto Nazionale di Ricerca Metrologica, Torino, Torino, Italy, 3Centre for the Developing Brain, Kings College London, London, United Kingdom, 4Division of Imaging Sciences and Biomedical Engineering, Kings College London, London, United Kingdom, 5Neuroimaging Analysis Centre, University College London Hospitals, London, United Kingdom, 6Dip. Energia, Politecnico di Torino, Torino, Italy

Heating Ti6Al4V and CoCrMo bilateral hip prostheses in a human body voxel model exposed to individual and combined 1 kHz magnetic fields associated with a conventional multi-axis gradient (30 mT m-1) coil set was predicted using a non-commercial frequency-domain code based on hybrid finite element (FE) - boundary element (BE) method. For CoCrMo (Ti6Al4V) prostheses, maximum increases of 1.2 (0.7), 0.3 (0.18) and 1.4 (1.2) oC were predicted, respectively, for x, y and z coils individually and of 2.0 (1.2) oC when combined. The temperature rise when all three gradients are used intensively is of concern, particularly for CoCrMo implants.

4879.   62 An 8 Channel Transmit Receive Sodium & Nested 8 Channel Transmit Receive Proton Coil for 3.0 T Brain Imaging
Karthik Lakshmanan1, Ryan Brown1, Guillaume Madelin1, Fernando Boada1, and Graham Wiggins1
1Department of Radiology, New York University School of Medicine, NewYork, NewYork, United States

Nested 8 Channel Tx/Rx Sodium array & A 8 Channel Proton array for 3.0 T Brain Imaging

4880.   63 Design and Application of a Nested Multi-Channel Sodium/Proton Knee Array at 3T
Ryan Brown1, Karthik Lakshmanan1, Guillaume Madelin1, Gregory Chang1, Daniel K Sodickson1, Ravinder R Regatte1, and Graham C Wiggins1
1The Bernard and Irene Schwartz Center for Biomedical Imaging, Dept. of Radiology, New York University School of Medicine, New York, NY, United States

We describe a six channel proton/sodium 3T knee array whose design counteracts low coil-tissue coupling that is characteristic of low-gamma coils and can make the potential gains from a phased array difficult to realize. This issue was addressed by implementing 1) a mechanically flexible former to minimize coil-to-tissue distance and reduce the overall diameter of the array, and 2) a wideband matching scheme that counteracts preamplifier noise degradation caused by resonance frequency splitting and a high loaded coil quality factor. The sodium array provided at least 30% SNR gain over a birdcage coil, while proton channel performance was sufficient for clinical imaging.

4881.   64 Design and Testing of a 9-Channel Phased Array Coil for Magnetic Resonance Guided Focused Ultrasound Treatment of the Abdominal Region in Large Animal Models.
Emilee Minalga1, Robb Merrill1, Allison Payne1, Nassir F. Marrouche2, Dennis L. Parker1, and J. Rock Hadley1
1Radiology, University of Utah, Salt Lake City, UT, United States, 2Comprehensive Arrhythmia Research and Management (CARMA) Center, University of Utah, Salt Lake City, UT, United States

Coils that increase the SNR for MRgFUS treatments are very important. More signal-to-noise ratio can give better temperature measurements which increases the treatment efficacy and safety. This work describes the design and testing of a 9-channel radio-frequency coil array designed for abdominal magnetic resonance guided focused ultrasound research in large animal models.

4882.   65 Excitation Performance and SAR Control with Z-Stacked Body RF Coil Arrays in Parallel Transmission at 3T
Xiaotong Zhang1, Xiaoping Wu2, Jinfeng Tian2, Sebastian Schmitter2, Lance DelaBarre2, Michael Hamm3, Josef Pfeuffer3, Dingxin Wang2,4, Bin He1,5, Thomas Vaughan2, Kamil Ugurbil2, and Pierre-Francois Van de Moortele2
1Department of Biomedical Engineering, University of Minnesota, Minneapolis, MN, United States, 2Center for Magnetic Resonance Research, University of Minnesota, Minneapolis, MN, United States, 33Siemens Healthcare, MR Application Development, Erlangen, Germany, 4Siemens Medical Solutions USA Inc, Minneapolis, MN, United States, 5Institute for Engineering in Medicine, University of Minnesota, Minneapolis, MN, United States

A High Pass birdcage (32 rungs) driven on two quad ports (1x2) and three TEM whole body arrays consisting of one ring (1x8), 2 z-stacked rings (2x8) or 3 z-stacked rings (3x8) of TEM elements (8 per ring) have been modeled. Their performance in parallel transmission on spine and brain+c-spine imaging has been evaluated, in which the excitation fidelity, RF power, global SAR and peak 10gSAR are compared. RF Spoke placement impact is also detailed for different coil designs.

4883.   66 Adaptive Head Array
Victor Taracila1, Miguel Navarro1, Darren Gregan1, Sarah Ortman1, and Fraser Robb1
1General Electric Healthcare, Aurora, Ohio, United States

Brain imaging became one of the main applications in MRI. A high performance brain coil needs to have the receiving elements as close as possible to the ROI. Unfortunately with the big variation within the human population head sizes, the head coils are usually made to fit the 99 percentile of the people, therefore for smaller size people the coil could under perform. There are attempts to address different head size populations with appropriately sized coils. We propose to change the paradigm of a rigid head coil, but still accomplish the goal of one-size-fits-all coil – the Adaptive Head Array (AHA).

4884.   67 B1 Homogenization and Local SAR Reduction Using B1-control Receive Array Coil at 3T
Yukio Kaneko1, Yoshihisa Soutome1,2, and Hisaaki Ochi1
1Hitachi Ltd., Central Research Laboratory, Kokubunji, Tokyo, Japan, 2Hitachi Medical Corporation, Kashiwa, Chiba, Japan

B1 inhomogeneity increases as the strength of a magnetic field increases. Various methods to reduce the B1 inhomogeneity have been developed. However, B1 inhomogeneity still remains in some cases of abdominal imaging. A more effective method is therefore required. In this study, a B1-control receive array coil (BRAC), which has the inductive mode during the RF transmit period, was designed. The B1 field and local SAR field in a human model were calculated in FDTD simulation. It is shown that the BRAC can reduce B1 inhomogeneity and local SAR in the human body.

4885.   68 A 60-Channel Ex-Vivo Brain-Slice Coil Array for 3T Imaging
Bernhard Gruber1,2, Boris Keil2, Thomas Witzel2, Aapo Nummenmaa2, and Lawrence L Wald2
1School of Applied Health and Social Sciences - Medical Engineering, University of Applied Sciences, Linz, Upper Austria, Austria, 2Department of Radiology, Massachusetts General Hospital, Harvard Medical School, A.A. Martinos Center for Biomedical Imaging, Charlestown, Massachusetts, United States

The parallel acquisition of brain images is standard nowadays. A wide range of coils offering specialized solutions to problems in clinical diagnosis, preclinical science and research already exists but to proceed with the imaging of the human brain for the “Human Connectome Project” a 60 Channel Receive Array Coil for ex-vivo brainslices at 3 Tesla was constructed. This coil was developed for research purposes only, but other applications, especially in pathology or clinical applications, are possible out of the design.

4886.   69 Combined Transmit-Only Asymmetric Birdcage and Receive-Only Endorectal Surface RF Coils
Adam Farag1, Justin Peterson2, Trevor Wade1, Trevor Szekeres1, Alexei Ouriadove3, Eli Gibson4, Aaron Ward4, Joseph Chin5, Steven Pautler6, Glenn Bauman5, Cesare Romagnoli5, Robert Bartha1,2, and Timothy Scholl1,2
1Robarts Research Institute, Western University, London, ON, Canada, 2Medical Biophysics, Western University, London, ON, Canada, 3Thunder Bay Regional Research Institute, ON, Canada, 4Biomedical Engineering, Western University, ON, Canada, 5London Health Science Center, ON, Canada, 6St. Joseph's Health Care, ON, Canada

Though radio frequency (RF) coil is a well-established science, the challenges that an RF designer faces when applying them to MRI are unique. Particularly, the challenges of developing confined RF coil for the purpose of insertion and imaging small parts in the human body, is different. In this work we present a low frequency Endorectal RF coil for measuring sodium tissue concentration (TSC) in the prostate. This has the potential to enable researchers to understand the sodium and cancerous cells relationship. First images at 3T were obtained and analysed, coil sensitivity was corrected and measurements of TSC is possible.

4887.   70 Why do dipole antennas work? A comparison to loop coils as a function of element size
Alexander Raaijmakers1, Peter R. Luijten1, and Cornelis A.T. van den Berg2
1Radiology, UMC Utrecht, Utrecht, Utrecht, Netherlands, 2Radiotherapy, UMC Utrecht, Utrecht, Netherlands

More and more institutes have recognized the potential of dipole antennas. However, many coil engineers are still reluctant to adopt this new technology. This abstract will provide a meaningful insight into why dipoles can outperform more conventional coil array elements at ultra-high fields. A comparison to loop coils is performed by FDTD simulations at 300 MHz with varying dimensions. Results show that large dimensions are only beneficial at large depths. Dipole antennas outperform loop coils from a depth of only 5 cm. These results confirm again that dipole antennas form a promising candidate to improve ultra-high field imaging performance.


RF Safety

Thursday 15 May 2014
Exhibition Hall  14:30 - 15:30

  Computer #  
4888.   49 SAR characterisation for parallel transmission MRI – comparison between modelling different decoupling regimes
Arian Beqiri1, Jeff W. Hand1, Francesco Padormo1,2, Joseph V. Hajnal1,2, and Shaihan J. Malik1
1Division of Imaging Sciences and Biomedical Engineering, King's College London, London, United Kingdom, 2Centre for the Developing Brain, King's College London, London, United Kingdom

In this study we compare different ways of modelling decoupling in parallel transmission MRI systems using EM solver simulations. One method is to model the individual transmit elements independently without including any decoupling networks leading to an ideally decoupled system. The other method involves using circuit co-simulation to model the entire system fully along with the decoupling networks. Here we compare the fields produced between the two methods and their estimates of SAR showing that they both give comparable results.

4889.   50 A Novel Method for MRI Safe Lead Design
Volkan Acikel1,2 and Ergin Atalar1,2
1Department of Electrical and Electronics Engineering, Bilkent University, Ankara, Turkey, 2National Magnetic Resonance Research Center (UMRAM), Ankara, Turkey

In this study a novel method for designing MRI safe leads using Modified Transmission Line Method (MoTLiM) is presented. SAR at the tip of a lead is formulated and it is shown that by adjusting the wavenumber along the lead SAR can be decrease significantly. A way to increase wavenumber is multilayer wound leads. In multilayer wound leads, resistance increases due to the proximity effect and inductance increase due to the number of windings. It is shown that by increasing number of layers SAR can be decreased such that the implant lead tip heating is no longer a significant problem.

4890.   51 Experience in imaging healthy volunteers and patients with implants at 7T
Yacine Noureddine1,2, Andreas K. Bitz2,3, Markus Thürling2,4, Karsten H. Wrede5, Mark E. Ladd2,3, Gregor Schaefers1, and Oliver Kraff2,6
1MR:comp GmbH, Dept. of Consulting, MR safety testing Laboratory, Gelsenkirchen, NRW, Germany, 2Erwin L.Hahn Institute for MRI, University Duisburg-Essen, Essen, NRW, Germany, 3Division of Medical Physics in Radiology, German Cancer Research Center (DKFZ), Heidelberg, BW, Germany, 4Department of Neurology, University Duisburg-Essen, Essen, NRW, Germany, 5Clinic for Neurosurgery, University Hospital Essen, Essen, NRW, Germany, 6Department of Diagnostic and Interventional Radiology and Neuroradiology, University Hospital Essen, Essen, NRW, Germany

Examination of patients with implants has become relevant at research facilities with ultra-high field strength systems. Nevertheless, no standards or tests currently exist for implants at 7T due to the more complex and specific challenges at this field strength. Many 7T research centers conservatively exclude all subjects with implants, regardless of type or loca-tion. This study presents our 7-year experience in imaging patients and healthy volunteers with implants other than dental implants at 7T.

4891.   52 Reliable and robust RF safety assessment of transmit array coils at ultrahigh fields
Frank Seifert1, Antonino Cassara1, Gerd Weidemann1, and Bernd Ittermann1
1Physikalisch-Technische Bundesanstalt (PTB), Berlin, Germany

A reliable simulation based assessment of RF safety of pTX-coil-arrays requires an elaborate estimation of upper limits of local SAR for all reasonable steering conditions and model assumptions. Limiting the forward power of each individual transmit channel is the simplest and most reliable approach to comply with applicable safety standards. For these circumstances we propose a simple estimation procedure to find an upper limit for local SAR from the Q-matrix. When applying this procedure to a 7T 8-channel transmit head coil the resulting local SAR related power limit is only 25 percent lower than the power limit for the head SAR which has to be maintained anyway.

4892.   53 RF safety evaluation of different configurations of high-permittivity pads used to improve imaging of the cerebellum at 7 Tesla
Andreas K. Bitz1,2, Oliver Kraff2, Stephan Orzada2, Tim Herrmann3, Johannes Mallow3, Johannes Bernarding3, and Mark E. Ladd1,2
1Medical Physics in Radiology, German Cancer Research Center (DKFZ), Heidelberg, Germany, 2Erwin L. Hahn Institute for Magnetic Resonance Imaging, University Duisburg-Essen, Essen, Germany, 3Department of Biometrics and Medical Informatics, Otto-von-Guericke-University Magdeburg, Magdeburg, Germany

Dielectric pads with high permittivity can be used to improve image quality in UHF brain imaging. To achieve this, the positions of the pads have to be optimized individually for each examination, leading to different configurations which need to be analyzed w.r.t. RF safety. Therefore, detailed RF exposure analysis based on RF simulations has been performed to check whether the maximum permissible input power of the Tx coil needs to be readjusted. Results show that the SAR distribution is influenced by the high-permittivity pads and depends on their size and orientation. For certain configurations, a significant SAR elevation was found.

4893.   54 The Feasibility of Predicting Temperature Increase through Local SAR Estimation via Electrical Properties Tomography: A Phantom Study at 7T
Xiaotong Zhang1, Jiaen Liu1, Pierre-Francois Van de Moortele2, Sebastian Schmitter2, and Bin He1
1Department of Biomedical Engineering, University of Minnesota, Minneapolis, MN, United States, 2Center for Magnetic Resonance Research, University of Minnesota, Minneapolis, MN, United States

It has been shown that Electrical Properties (EPs) of biological tissues can be derived from MR-based B1 measurement. A strong appeal for these ‘Electrical Property Tomography’ (EPT) methods is to estimate real-time and subject-specific local SAR induced by RF pulsing. In order to investigate the feasibility of EPT-based SAR estimation in predicting possible local temperature change, following previously proposed EPT protocols, in this preliminary study, induced local SAR in a saline phantom has been estimated for a heating sequence at 7T, as compared to measured temperature changes using MRI Thermometry based on the proton chemical shift (PRF).

4894.   55 Investigation of Different RF Coil Safety Assessment Techniques: E-field Measurements, EM Field Simulations and MR Thermometry
Cem Murat Deniz1,2, Leeor Alon1,2, Gene Y Cho1,2, Ryan Brown1, Christopher M Collins1,2, and Daniel K. Sodickson1,2
1The Bernard and Irene Schwartz Center for Biomedical Imaging, Department of Radiology, New York University School of Medicine, New York, NY, United States, 2The Sackler Institute of Graduate Biomedical Sciences, New York University School of Medicine, New York, NY, United States

Electromagnetic field simulations and MR thermometry measurements have been used for evaluating the safety of RF coils. Increasingly, electric field measurements have been employed as an additional validation of electromagnetic field simulations, and as a means of assessing the safety of RF antennas. In this work, we investigated the application of these RF coil safety assessment techniques using a dipole antenna and "SAM" head phantom. Our results indicate that all three methods provide comparable RF safety information both in pattern and in magnitude.

4895.   56 Fast method to compute the electromagnetic field inside a model of the human head surrounded by a dielectric pad
Giuseppe Carluccio1, Switt Kittivittayakul2, Piergiorgio Uslenghi2, Christopher Michael Collins1, and Danilo Erricolo2
1Bernard and Irene Schwartz Center for Biomedical Imaging, New York University School of Medicine, New York, New York, United States, 2Electrical and Computer Engineering, University of Illinois at Chicago, Chicago, Illinois, United States

High permittivity dielectric pads have become popular for their ability to locally enhance the B_1 field in the region of interest, especially in tissues close to the pad. Commonly, it is challenging to have a strong signal in regions close to the center of the head, and it is hard to predict the effect of the use of dielectric materials in those locations. In this work a fast exact analytical method is proposed to compute the electromagnetic field at the center of a model of the human head. The method can be useful to design optimal dielectric pads.

4896.   57 Numerical simulations of RF heating for infants within MR body coil
Xin Chen1, Charles Poole2, Michael Steckner1, and Robert Brown2
1MR, Toshiba Medical Research Institute USA, Inc., Mayfield Village, OH, United States, 2Physics, Case Western Reserve University, Cleveland, OH, United States

MRI is useful for neonatal/pediatric imaging since no ionizing radiation is used. Nevertheless, MRI has unique safety concerns: RF power deposition and resultant tissue heating. Numerical simulations have been widely applied to investigate specific absorption rate (SAR) and tissue temperature rise. However, most work published on adults and only a few showed results for infants. Infants’ (especially neonates) thermoregulation is not as developed as adults, and may be further impaired under unique scan conditions (sedation, swaddling). Furthermore, there are no special considerations in regulatory limits for these patients. This work investigates SAR and temperature rise in infants due to RF heating.

4897.   58 Fast Local SAR Simulation by Domain-Decomposition
Shumin Wang1
1Auburn University, Auburn, AL, United States

Real-time Local SAR simulation is critical to the success of multi-channel RF transmission at high fields. The speed of conventional electromagnetic simulation methods is insufficient even on parallel computation platforms. We propose a novel domain-decomposition method that applies different numerical algorithms in the interior and the exterior of a human body model. These different methods then interface on the surface of the human body model. Preliminary studies show that on a single-core CPU, simulating an eight-channel brain imaging array only in 30 seconds.

4898.   59 Direct SAR Mapping by Thermoacoustic Imaging: A Feasibility Study
Simone Angela Winkler1, Paul Picot2, Michael Thornton2, and Brian K Rutt1
1Dept of Radiology, Stanford University, Stanford, California, United States, 2Endra, Inc., Ann Arbor, Michigan, United States

We propose a new concept for direct measurement of specific absorption ratio (SAR), to be used as a safety assessment / monitoring tool for MRI. The concept uses short bursts of RF energy and measures the resulting thermoacoustic excitation pattern by an ultrasound transducer array, followed by image reconstruction to yield the 3D SAR distribution. We developed a simulation framework to model this thermoacoustic SAR mapping concept; results of these simulations show good agreement between reconstructed and original SAR distributions and support the feasibility of direct experimental mapping of SAR distributions in vivo.

4899.   60 RF Safety Evaluation for Neonatal MRI at 3T
Shaihan J Malik1, Arian Beqiri1, Anthony N Price1,2, Jeff W Hand1, and Joseph V Hajnal1,2
1Division of Imaging Sciences and Biomedical Engineering, Kings College London, London, London, United Kingdom, 2Centre for the Developing Brain, Kings College London, London, London, United Kingdom

Algorithms used by scanner manufacturers usually control SAR using adult based models. In this study whole body and 10 g local averaged SARs in a newborn neonate head- or heart-centred in a 127 MHz birdcage coil were predicted numerically. SARs were scaled to match the duty cycle used in a Philips 3T Achieva when run at body scanning and head scanning SAR limits, mimicking the scanner set-up process during automated power scaling when an adult subject is present. Results indicate that under these conditions, exposure of a neonate is conservative from a safety point of view.

4900.   61 B1+-based SAR assessment using a birdcage coil at 7 Tesla: experimental evaluation using magnetic resonance thermometry
Nicolas Boulant1, Ulrich Katscher2, Michel Luong1, Aurelien Massire1, Alexis Amadon1, and Alexandre Vignaud1
1Neurospin, CEA, Saclay, Ile de France, France, 2Philips Research Europe, Hamburg, Germany

The emerging field of Electric Properties Tomography has shown great promise to provide patient-specific information about the electric field via the post-processing of measured B1+ data utilizing Maxwell’s equations. The work of Voigt et al furthermore showed a good correlation between the numerically determined SAR distribution and the one based on the post-processing of the B1+ field at up to 3T, but with a global offset between the two. The purpose of this work was to experimentally evaluate this B1+-based SAR determination via MR temperature-based measurements at 7T with a birdcage coil on a phantom of known electrical properties.

4901.   62 The Effect of Brain Tumors on Local SAR Levels at 7T
Matthew C. Restivo1, Cornelis A.T. van den Berg1, Astrid L.H.M.W. van Lier1, Daniël L. Polders1, Alexander J.E. Raaijmaker1, Peter R. Luijten1, and Hans Hoogduin1
1Imaging Division, University Medical Center Utrecht, Utrecht, Netherlands

It is well known that specific absorption rate (SAR) is highly dependent on tissue conductivity. Previous work has shown that brain tumors have increased conductivity compared to surrounding tissues. In this work, we analyzed the effects of brain tumors on simulated local SAR levels at 7T. We segmented dielectric tissues from T1w scans of three actual tumor patients. We then assigned realistic conductivity values that were known from 7T Electrical Property Tomography of the same patients. We are able to show that the presence of tumors increases SAR locally, although not to the extent that we predict.

4902.   63 Calculation of 10g average SAR via inversion of the heat equation using MRI Thermometry and Thermal Property Measurements
Leeor Alon1,2, Gene Cho1,2, Leslie F. Greengard3, Ricardo Otazo1,2, Daniel K. Sodickson1,2, and Cem M. Deniz1,2
1Department of Radiology, Bernard and Irene Schwartz Center for Biomedical Imaging, New York University School of Medicine, New York, NY, United States, 2Sackler Institute of Graduate Biomedical Sciences, New York University School of Medicine, New York, NY, United States, 3Courant Institute of Mathematical Sciences, New York University, NY, United States

RF safety of MRI coils is often evaluated by conducting RF heating experiments on tissue mimicking phantoms inside the scanner room. Because of power delivery capabilities of RF amplifiers, long RF heating durations (>6 minutes) are required to create a temperature change that can be accurately detected by MR thermometry measurements. In such cases when the heating duration is long, conversion from temperature-change to SAR is nontrivial, since the heat-diffusion effect is prominent and direct scaling of the temperature change with heat capacity yields large 10g average SAR errors (~55% , shown as in this abstract ). In this work, a method for 3D calculation of 10g average SAR is presented via inversion of the heat equation using high-resolution 3D temperature maps and measured thermal properties of the phantom. The algorithm can be used to calculate 10g average SAR experimentally for limiting RF energy deposition from physical coils in the scanner room with small errors, %3.1.

4903.   64 Building a computational model of a transmit body coil: considerations for RF safety.
Elena Lucano1, Gonzalo Mendoza1, Tom Lloyd2, Steve Wedan2, Wolfgang Kainz1, and Leonardo Angelone1
1Office of Science and Engineering Laboratories, Division of Physics, US Food and Drug Administration, Center for Devices and Radiological Health, Silver Spring, MD, United States, 2Imricor Medical Systems, Burnsville, MN, United States

Numerical models have been used to evaluate the potential for radiofrequency induced heating of medical devices in a MR environment. The aim of this study was to evaluate three model designs with respect to their accuracy in simulating the electromagnetic field generated by a body coil. The experimental validation showed that all three of the numerical models properly simulated the magnetic field distribution. However, to represent the true electric field and avoid possible overestimation by several orders of magnitude, accurate modeling of the tuning capacitors, coil losses, and source configuration was required.

4904.   65 A Fast Method to Estimate SAR Distribution from Temperature Images Highly Affected by Noise
Giuseppe Carluccio1, Florian Knoll1, Cem Murat Deniz1, Leeor Alon1, and Christopher Michael Collins1
1Bernard and Irene Schwartz Center for Biomedical Imaging, New York University School of Medicine, New York, New York, United States

Even though temperature increase has a direct relationship to risk, local 10g average SAR is still the quantity most used to assess safety with reference to existing guidelines. MR thermometry allows measurements of temperature distribution through a cross-section of the sample. Inverting a method to estimate temperature from SAR, we have proposed a method to estimate SAR from temperature maps which is highly insensitive to noise, which often strongly affects temperature maps acquired with MR thermometry.

4905.   66 Fast Whole-Body Temperature Estimation for Real-Time MRI Safety Assurance
Giuseppe Carluccio1 and Christopher Michael Collins1
1Bernard and Irene Schwartz Center for Biomedical Imaging, New York University School of Medicine, New York, New York, United States

A method to quickly estimate the temperature increase by SAR absorption through the entire MRI exam. Using the linearity of the bioheat equation, the method convolves the precalculated temperature responses of the body tissues with the sequence of SAR segments applied during the exam. The predicted temperature distribution has been compared with the one obtained with a full Finite Difference Method solving the Pennes’ bioheat equation. The difference in the maximum temperature between the two methods was less than 1%, but in a computation time more than 30 times shorter.

4906.   67 Automatic Segmentation Pipeline for Patient-Specific MRI Tissue Models
Angel Torrado-Carvajal1,2, Juan A. Hernandez-Tamames1,2, Joaquin L. Herraiz2, Yigitcan Eryaman2,3, Elfar Adalsteinsson4,5, Lawrence L. Wald3,5, and Norberto Malpica1,2
1Dept. of Electronics, Universidad Rey Juan Carlos, Mostoles, Madrid, Spain, 2Madrid-MIT M+Vision Consortium in RLE, MIT, Cambridge, Massachusetts, United States, 3Dept. of Radiology, MGH, Martinos Center for Biomedical Imaging, Charlestown, Massachusetts, United States, 4Dept. of Electrical Engineering and Computer Science, MIT, Cambridge, Massachusetts, United States, 5Harvard-MIT Health Sciences and Technology, MIT, Cambridge, Massachusetts, United States

Specific absorption rate (SAR) may cause unsafe tissue heating in High-Field MRI scanners. We propose a pipeline for patient-specific tissue modeling based only on MRI data that could enable patient-specific pulse design in High-Field MRI. We used open-source tools to automatically segment eleven tissue classes: brain white matter (WM), gray matter (GM), cerebrospinal fluid (CSF), cerebellum WM and GM, skull, skin, eyeballs, main arteries, muscle and fat/cartilage. The method was tested in 12 healthy subjects, and its accuracy was confirmed by an expert radiologist. The models are automatically meshed and exported in a format compatible with EM simulation software.

4907.   68 Anatomically Detailed Human Head Phantom for MR Testing Purposes
Sossena Wood1, Narayanan Krishnamurthy1, Yujuan Zhao1, Shailesh Raval1, Tiejun Zhao2,3, J. Andy Holmes4, and Tamer Ibrahim, PhD1
1Bioengineering, University of Pittsburgh, Pittsburgh, PA, United States, 2Siemens Medical System, Pittsburgh, PA, United States, 3University of Pittsburgh, Pittsburgh, PA, United States, 4Swanson Center for Product Innovation, University of Pittsburgh, Pittsburgh, PA, United States

This research was performed because there are several issues experienced at higher field strengths that hinder its clinical potential resulting in a concern of the radiofrequency (RF) power absorption in tissue and local temperature rising. These concerns, mainly safety, are evaluated through electromagnetic simulations that are compared to phantoms. However, most phantoms are not realistic nor comparable to the anatomical detail of a human head.

4908.   69 A Statistical Study of Head Models for Local SAR Simulation
Yu Shao1, Peng Zeng2, and Shumin Wang2
1Auburn University, Auburn, Alabama, United States, 2Auburn University, Alabama, United States

Subject-specific local SAR analysis is critical to the safety of multi-channel transmission at high fields. In order to calculate the local SAR, subject numerical models need to be constructed at first. However, highly detailed subject models may not be available because they require high-resolution images, which in turn require the local SAR problem to be solved at first place. In a previous study, it was found that three-tissue water/fat/air model is sufficiently accurate for local SAR analysis at 3 Tesla. In this study, we shall apply a statistical approach to find the appropriate simplification of head models and its accuracy.

4909.   70 Body Models of Big People for MRI Safety Assessment
Ingmar Graesslin1, Hanno Homann1, Holger Eggers1, Kay Nehrke1, Paul Harvey2, Cecilia Possanzini2, and Peter Börnert1
1Philips Research Laboratories, Hamburg, Germany, 2Philips Healthcare, Best, Netherlands

Estimating the specific absorption rate (SAR) is a challenge for parallel transmission MRI systems, because the SAR depends on subject- and coil-specific parameters. In this work, we present a novel approach to generate whole-body models for SAR simulations of very large subjects. The new concept uses 2D multi-station imaging with lateral virtual FOV enlargement and a water/fat separating imaging sequence. The main application area is the development of patient-specific body models for SAR assessment, which may enable improved SAR management and reduced scan time in parallel transmit MRI. This approach can be used for potential basic diagnostic applications using 2D and 3D imaging techniques.

4910.   71 Rapid, Direct Measurement of Bulk RF Power Deposition using Free Induction Decay Acquisitions
Leeor Alon1,2, Assaf Tal1,2, Giuseppe Carluccio1,2, Cem M. Deniz1,2, Karthik Lakshmanan1,2, Daniel K. Sodickson1,2, and Christopher C. Collins1,2
1Department of Radiology, Bernard and Irene Schwartz Center for Biomedical Imaging, New York University School of Medicine, New York, NY, United States, 2Sackler Institute of Graduate Biomedical Sciences, New York University School of Medicine, New York, NY, United States

Whole body and partial body RF power deposition is typically monitored by estimating the RF power delivered to the patient in the scanner. In practice however, some portion of the energy gets deposited in the transmit chain and coil electronics and different subjects couple to the coil differently so that the RF power deposited into the patient may be overestimated. In this work, we utilize a single excitation pulse and acquire a single FID before and after exposure to SAR to measure the RF thermal energy change. Results are shown for phantom and in-vivo heating experiments.