ISMRM 24th Annual Meeting & Exhibition • 07-13 May 2016 • Singapore

Traditional Poster Session: MR Safety

2209 -2240 MR Safety

MR Safety

Magnetically Induced Force Measurements per ASTM F2052 of Active Implantable Medical Device Lead Materials
Michael Childers1, Roya Hashemi Rad1, Richard Williamson1, and Shiloh Sison1
1St. Jude Medical, Sylmar, CA, United States
This abstract presents magnetically induced force measurements per ASTM F2052 of materials commonly used in implantable leads.  Implantable leads which are constructed solely from tested materials which pass the magnetically induced force testing acceptance criteria (i.e. gravity force), may not require magnetically induced force testing per ASTM F2052 for MR conditionality with 3 T MR scanners.


Detailing the MR Safety of Intraocular Tantalum Markers Used for Treatment Planning of Proton Beam Therapy of Uveal Melanoma: A 7.0T Study
Eva Oberacker1, Katharina Paul1, Lukas Winter1, Celal Oezerdem1, Antje Els1, Andreas Pohlmann1, Laura Boehmert1, Stefanie Kox1, Min-Chi Ku1, Till Huelnhagen1, Oliver Stachs2, Jens Heufelder3,4, Andreas Weber3,4, and Thoralf Niendorf1,5
1Berlin Ultrahigh Field Facility (B.U.F.F.), Max Delbrück Center for Molecular Medicine in the Helmholtz Association, Berlin, Germany, 2Department of Ophthalmology, University of Rostock, Rostock, Germany,3Department of Ophthalmology, Charité University Medicine, Berlin, Germany, 4BerlinProtonen, Helmholtz Zentrum Berlin, Berlin, Germany, 5Experimental and Clinical Research Center (ECRC), a joint cooperation between the Charité Medical Faculty and the Max Delbrück Center for Molecular Medicine in the Helmholtz Association, Berlin, Germany
This work examines the MR safety of intraocular tantalum markers used in proton beam therapy of uveal melanoma. RF power deposition induced heating was studied using electromagnetic field and temperature simulations. Magnetic force acting on the marker was investigated and image artifacts were assessed. Minor local increase of RF power deposition was observed for SAR0.075g but not detectable for SAR1g. Measurements showed no detectable magnetic attraction of the implant. FSE based imaging showed only small artifacts barely exceeding the thickness of the sclera. Our studies indicate that intraocular tantalum markers do not constitute a per se contraindication for 7.0T MRI.


SAR/B1+ calibration workflow for safe, high duty-cycle parallel transmission imaging at ultra-high field
Filiz Yetisir1, Bastien Guerin2, Lawrence Wald2,3, and Elfar Adalsteinsson1,3
1Electrical Engineering and Computer Science, Massachusetts Institute of Technology, Cambridge, MA, United States, 2Dept.of Radiology, Martinos Center for Biomedical Imaging, Charlestown, MA, United States,3Harvard-MIT Division of Health Sciences Technology, Institute of Medical Engineering and Science, Cambridge, MA, United States
In this work, we propose a pTX safety workflow that will enable high duty cycle imaging at high field systems. Several SAR and B1+ calibration steps are suggested for a complete analysis including modeling the TX array, testing it over time and different loads and finding a safety margin to account for RF system imperfections. Good qualitative agreement was achieved between the simulated and measured B1+ maps for the TX array. 11% and 6° standard deviation was observed in the magnitude and the relative phase maps over time. A maximum difference of 16% was observed between offline and online calculated local SAR values due to RF system imperfections.


Direct optical measurement of the RF electrical field for MRI
Isabelle Saniour1, Anne-Laure Perrier2, Gwenaël Gaborit2,3, Jean Dahdah3, Lionel Duvillaret3, and Olivier Beuf1
1CREATIS, Université de Lyon ; CNRS UMR5220 ; Inserm U1044 ; INSA-Lyon ; Université Claude Bernard Lyon 1, Villeurbanne, France, 2IMEP-LAHC, UMR 5130 ; Université de Savoie, Le Bourget-du-Lac, France,3Kapteos, Sainte-Hélène du Lac, France
In MRI, a real time monitoring of the magnitude of the electric field prevents the patient from safety hazards due to heating phenomenon. A sub-cm electro-optical probe was used to localize and measure the E-field in 4.7-T MRI. This probe is formed from an electro-optic crystal that changes its refractive indexes according to the applied E-field. The results show that the probe is non-perturbative regarding the E-field and does not affect the quality of MR images. Six clear E-field concentrations were localized at proximal and distal sides of the transceiver coil. Their magnitudes vary between 10000V/m and 20000V/m.   


On Peripheral Nerve Stimulation of a Compact, Asymmetric Head-Only Gradient Coil: Head Orientation Dependence
Seung-Kyun Lee1, Kishore V. Mogatadakala2, Dominic Graziani1, Jean-Baptiste Mathieu2, Thomas K.-F. Foo1, and Matt A. Bernstein3
1GE Global Research, Niskayuna, NY, United States, 2GE Healthcare, Florence, SC, United States, 3Mayo Clinic, Rochester, MN, United States
Head orientation dependence of the peripheral nerve stimulation (PNS) thresholds and the induced electric fields of a high-performance, asymmetric head-only gradient coil were studied experimentally and by numerical simulation. In the experiment, the gradient field direction was fixed and the subject head was rotated in the transverse plane. The subject-reported PNS thresholds nearly doubled when the head's anterior-posterior direction was parallel to the gradient compared to when the head was approximately perpendicular to the gradient. Human-body-model simulation suggested that the orientation dependence may be primarily due to locally concentrated electric fields in the corrugated regions of the face.


Positioning to decrease hot spots caused by an intramedullary rod implanted in a forearm
Yu Kikuchi1, Minghui Tang1, and Toru Yamamoto2
1Graduate School of Health Sciences, Hokkaido university, sapporo, Japan, 2Faculty of Health Sciences, Hokkaido university, sapporo, Japan
RF heating causes most of incidents during MRI examinations. There still are patients who were implanted metallic products before the advent of MRI and MR compatibility of most such products is unknown.  It was reported that an MRI examination of a patient implanted an intramedullary rod in his forearm was aborted due to a heating claim from the patient. In this study, we confirm RF heating of such patient by using an electromagnetic analysis software dedicated for MRI, and shows that positioning of an implanted arm can decrease SAR sufficiently enough to take MRI examinations.


Assessment of Radio Frequency Induced Heating On or Near Implants during MRI – some open issues
Mikhail Kozlov1,2 and Gregor Schaefers1,3
1MR:comp GmbH, Gelsenkirchen, Germany, 2Max Planck Institute for Human Cognitive and Brain Sciences, Leipzig, Germany, 3Magnetic Resonance Institute for Safety, Technology and Research GmbH, Gelsenkirchen, Germany
We evaluated locations of maximum temperature rise (max(ΔT)) and the dependence of maxT) on RF-induced power deposition (Ptotal) for some generic implants. ΔT spatial and temporal variations were investigated. To fulfill ASTM F2182-11a setup requirements, the temperature probe should be placed with submillimetre precision at location that cannot be predicted by a full wave electromagnetic simulation alone. It is a challenge to validate with small uncertainty Ptotal calculated using EM simulation by only measuring SAR or VLD value at some points in space, if the field probe sensor size is larger than one tenth of the wire diameter.


Reduction of the E field at the tip of implanted wires generated by pTx coils using RF current measurements
Gerd Weidemann1, Frank Seifert1, and Bernd Ittermann1
1Physikalisch-Technische Bundesanstalt (PTB), Braunschweig and Berlin, Germany
The possibility to reduce implant heating is an added value option of parallel transmission. An orthogonal-projection method (OPM) is presented to reduce the E fields at the tip of wire type implants by using voltage vectors orthogonal to the vector inducing the worst case RF current at the protruding end of the implant. Experiments confirm that the minimization of RF current at the protruding end leads to a distinct reduction of the electric field at the tip of the wire. Low-hazard steering conditions for n-element pTx coils can be determined in real time during an MR investigation from the measurement of only n complex valued RF currents at the protruding end of the implant.


Visualization and Localization of Implanted Devices with Parallel Transmit Array Using Reversed RF Polarization
Parnian Zarghamravanbakhsh1, John M Pauly1, and Greig Scott1
1Electrical Engineering, Stanford University, Stanford, CA, United States
The radiofrequency (RF) transmit field can induce current in implanted devices; therefore, it is essential to detect and minimize coupling to stimulator leads and guide-wire structures. Reverse polarization has been proposed as low-RF-power method to safely detect current in the implanted devices using birdcage coil. The purpose of this study is to demonstrate feasibility of combining knowledge of coil current and location with reverse polarization method using parallel transmit array to detect and localize implanted wires. 


Heating of lead electrodes disconnected from sacral stimulator during routine lumbar MRI at 3T with receive-only coil
Pallab K Bhattacharyya1, Howard Goldman2, Mark J Lowe1, Adrienne Quirouet2, and Stephen E Jones1
1Imaging Institute, Cleveland Clnic, Cleveland, OH, United States, 2Glickman Urological Institute, Cleveland Clnic, Cleveland, OH, United States
RF heating testing during lumbar scans of Medtronic Interstim II (Model 3058) implantable pulse generator (IPG) connected to Medtronic Quadipolar Nerve Stimulator Lead (Model 3889) at 3T whole body Siemens TIM Trio scanner with receive-only cervical-lumbar-thoracic coil was performed. Temperatures of the electrodes were measured by using fiber optic sensors with fluoroptic monitoring with the IPG and lead placed inside an ASTM gel phantom. No electrode heating was observed when the lead was connected with the IPG in any of the scans, while considerable heating was observed when the IPG was disconnected and taken out of the phantom.


Comparing RF heating simulations and experimental results in pTx coils: an evaluation of three simulation methods
Hongbae Jeong1, Peter Jezzard1, and Aaron Hess2
1FMRIB Centre, University of Oxford, Oxford, United Kingdom, 2Department of Cardiovascular Medicine, University of Oxford, Oxford, United Kingdom
In this study, we conducted thermal simulations using EM simulation software and compared these to proton resonance frequency (PRF) thermometry using an ultra-high-field MR phantom. RF heating was measured in the magnet environment using a PRF-based 3D GRE on a 8-channel pTx coil. Three types of simulation method were assessed and compared with experimental data. Amongst the three simulation methods the realistic capacitance simulation was closest to the experimental measurement. In conclusion, PRF RF heating measurements with real fiber optic temperature changes can be used to assess and validate different types of RF simulation. 


Statistical Equivalence Test Protocol for RF Performance of AIMD Systems
Li-Yin Lee1, Shiloh Sison2, Shi Feng3, Kishore Kondabatni4, and Richard Williamson5
1BioStatistics, St. Jude Medical, Sylmar, CA, United States, 2Electrical Engineering, St. Jude Medical, Sunnyvale, CA, United States, 3Electrical Engineering, St. Jude Medical, Sylmar, CA, United States, 4St. Jude Medical, Sylmar, CA, United States, 5Program Management, St. Jude Medical, Sylmar, CA, United States
Test methods for MRI safety and RF safety of AIMD systems has been defined through ISO/TS 10974 are cumbersome to perform on every device and lead combination.  A clear method for determination that two likely equivalent systems has not been described.  The Concordance Correlation Coefficient has been described for this purpose in assay comparison.  This paper evaluates the CCC method for RF equivalence in presence of measurement uncertainty, and confirms that the CCC method is simple and robust for this purpose.    


Modelling the RF safety of tattoo pigment ink for subjects undergoing 7 Tesla MRI
Hongbae Jeong1, Aaron Hess2, and Peter Jezzard1
1FMRIB Centre, University of Oxford, Oxford, United Kingdom, 2Department of Cardiovascular Medicine, University of Oxford, Oxford, United Kingdom
Despite many reports of skin burns in the region of tattoos, there are few safety studies concerning RF heating caused by tattoos. Manufacturers of tattoo ink are numerous and use a range of dye ingredients, making it difficult to assess the electromagnetic properties of each ink pigment. An anchor-shaped tattoo was modelled 1mm under the skin layer in the region of the cervical spine to predict a possible skin burn generated by RF coil. A simulation model of RF heating in tattoo pigment is proposed, which shows that certain tattoo pigments may lead to severe skin burns when performing high field MRI.


Heterogeneous gelatin-based head phantom for evaluating DBS heating
Clare McElcheran1, Benson Yang2, Fred Tam2, Laleh Golenstani-Rad3, and Simon Graham2
1University of Toronto, Toronto, ON, Canada, 2Sunnybrook Health Sciences Centre, Toronto, ON, Canada, 3Massachusetts General Hospital, Charlestown, MA, United States
A method to create a heterogeneous head phantom with long implanted wires to improve the evaluation of tissue heating surrounding deep brain stimulation (DBS) leads is presented.  The phantom consists of three different oil-in-gelatin dispersions with electrical properties that mimic grey matter, white matter and cerebral spinal fluid (CSF) as well as a human skull.  3D printing technology was used to create gelatin moulds and an acrylic casing.  A CT scan of the human skull was obtained to create a mesh-based digital representation.  Thus, the physical phantom has an associated mesh-based digital model which can be used in electromagnetic simulation.


Potentially hazardous materials left behind after an MRI installation
Ken E Sakaie1, Wanyong Shin1, and Lowe J Mark1
1Imaging Institute, The Cleveland Clinic, Cleveland, OH, United States
We share our experience discovering and removing metallic objects left behind after a routine MRI hardware upgrade. The results suggest that vigilance is necessary despite the routine nature of such an upgrade.


Increased Signal Intensity of brain structures on unenhanced T1-weighted images following 35 or more GBCA administrations
Yang Zhang1,2, Yan Cao1, George Shih1, Elizabeth Hecht3, and Martin R Prince1,4
1Radiology, Weill Cornell Medical Center, New York, NY, United States, 2Radiology, Qilu Hospital, Shandong University, Jinan, China, People's Republic of, 3Columbia University, New York, NY, United States, 4Radiology, Columbia University, New York, NY, United States
In 16 patients with 35 or more linear GBCA administrations increased T1 signal on unenhanced images was observed in dentate nucleus (100%), globus pallidus (100%), cerebral peduncles (100%), substantial nigra (88%), red nucleus (88%), colliculi (81%), posterior thalamus (75%), superior cerebellar peduncle (56%), internal capsule (50%), head of caudate nucleus (31%), body of caudate nucleus (25%) , whole thalamus (25%), pons (13%), anterior commissure (13%), posterior brain stem (6%), pituitary gland (6%), mammillary body (6%) and putamen (6%).  The source of T1 signal increase is unknown but may relate to GBCA administration. No clinical significance was identified.


Power deposition into a metallic hip prosthesis exposed to switched gradient fields
Luca Zilberti1, Oriano Bottauscio1, Mario Chiampi2, Jeffrey Hand3, Hector Sanchez Lopez4, Rüdiger Brühl5, and Stuart Crozier6
1Istituto Nazionale di Ricerca Metrologica, Torino, Italy, 2Dipartimento Energia, Politecnico di Torino, Torino, Italy, 3Division of Imaging Sciences and Biomedical Engineering, King’s College London, London, United Kingdom, 4Department of Engineering, Universitas Dian Nuswantoro, Semarang, Indonesia, 5Physikalisch-Technische Bundesanstalt, Berlin, Germany, 6School of Information Technology and Electrical Engineering, University of Queensland, St. Lucia, Australia
Concern has been recently raised about the possible heating of massive metallic implants, in particular hip prostheses, due to the gradient fields used in MRI. Thus, this contribution discusses the computation of the power density deposited by the magnetic field into the implant, which represents the first step to estimate the thermal heating. The analysis is based on numerical simulations, performed through a computational formulation applied to an anatomical model of the body. The results provide evidence of the role of the three gradient coil axes and of the different harmonic components of the signals in this power deposition process.


Testing of a compact ultrasound scanner for use inside clinical interventional MRI suite
Chi Ma1, Zaiyang Long1, Diana M Lanners1, Donald J Tradup1, Joel P Felmlee1, David A Woodrum1, Nicholas J Hangiandreou1, and Krzysztof R Gorny1
1Department of Radiology, Mayo Clinic, Rochester, MN, United States
The suitability of a compact Samsung ultrasound (US) system for real-time imaging guidance of treatment device positioning inside 1.5T interventional magnetic resonance imaging (iMRI) suite was assessed. The US system was tested in a proposed site-specific configuration. Magnetic displacement forces exerted by the static magnetic field on each of the US system components were estimated at the proposed locations. Image quality of both MRI and US systems with the US system set to different operating modes were evaluated.  Results demonstrate that this particular US system is suitable for use in the site-specific configuration at our 1.5T iMRI suite. 


An Evaluation of Radio Frequency Induced Power Deposition of Coaxial Leads with an Implant Model
Mikhail Kozlov1,2 and Gregor Schaefers1,3
1MR:comp GmbH, Gelsenkirchen, Germany, 2Max Planck Institute for Human Cognitive and Brain Sciences, Leipzig, Germany, 3Magnetic Resonance Institute for Safety, Technology and Research GmbH, Gelsenkirchen, Germany
We performed 3-D electromagnetic simulations of coaxial leads and numerically obtained the lead models to evaluate power deposition and the voltage induced at the lead proximal end with the lead models. No correlation between peak volume loss density and deposited powers at the tip and the ring was observed. In some cases deposited power at the ring exceeded deposited power at the tip. However further extensive simulations of induced heating behavior should be done before final conclusions regarding coax lead design preferences are made.


Influence of electrical properties of lead insulation on radio frequency induced heating during MRI
Mikhail Kozlov1,2 and Gregor Schaefers1,3
1MR:comp GmbH, Gelsenkirchen, Germany, 2Max Planck Institute for Human Cognitive and Brain Sciences, Leipzig, Germany, 3Magnetic Resonance Institute for Safety, Technology and Research GmbH, Gelsenkirchen, Germany
We evaluated the dependence of RF-induced power deposited at a hot spot (p) on insulating electrical properties for insulated stainless steel wires of 1.5 mm in diameter with insulation thickness of 0.5 mm. Lead transfer functions (TF) were obtained by 3-D electromagnetic simulations. TF and p depended significantly on electrical properties of insulation. Increased insulator conductivity resulted in decreased p. For all insulated wires investigated non-uniform RF excitation resulted in higher power deposition than uniform RF excitation.


Design and simulation of a nested 4 channel 1H and 3 channel 13C coil for glycogen NMR experiments in the calf muscle at 7 T
Sigrun Goluch1,2,3, Roberta Kriegl2,3, Elmar Laistler2,3, Martin Gajdošík 4,5, and Martin Krššák 1,4,5
1Division of Endocrinology and Metabolism, Department of Internal Medicine III, Medical University of Vienna, Vienna, Austria, 2MR Center of Excellence, Medical University of Vienna, Vienna, Austria, 3Center for Medical Physics and Biomedical Engineering, Medical University of Vienna, Vienna, Austria, 4High-Field MR Center, Department of Biomedical Imaging and Image-Guided Therapy, Medical University of Vienna, Vienna, Austria, 5Christian Doppler Laboratory for Clinical Molecular MR Imaging, Medical University of Vienna, Vienna, Austria
Due to the inherently low sensitivity of carbon-13 NMR, 13C spectroscopic experiments at 7T require specifically optimized double tuned local RF transceive arrays for high SNR, exhibiting sufficient electrical isolation between the arrays to enable 1H decoupling and high SAR efficiency as to not invoke SAR limits during proton decoupling. In this work we present the simulation and optimization of a 7 channel nested 1H/13C RF transceive coil array for 13C metabolic studies in the human calf muscle at 7 T.


Assessment of RF induced heating of intracranial Micro-depth electrodes during MRI
Anastasia Papadaki1,2, David Carmichael3, Andrew McEvoy4,5, Anna Miserocchi4,5, Tarek Yousry1,2, Beate Diehl4,6, Louis Lemieux4, and John S Thornton1,2
1Lysholm Department of Neuroradiology, National Hospital for Neurology and Neurosurgery, UCLH, London, United Kingdom, 2Department of Brain Repair and Rehabilitation, UCL Institute of Neurology, London, United Kingdom, 3Imaging and Biophysics Unit, UCL Institute of Child Health, London, United Kingdom, 4Department of Clinical and Experimental Epilepsy, UCL Institute of Neurology, London, United Kingdom,5Department of Neurosurgery, National Hospital for Neurology and Neurosurgery, London, United Kingdom, 6Department of Neurophysiology, National Hospital for Neurology and Neurosurgery, London, United Kingdom
In this study we assessed temperature changes (?T) during MRI in the vicinity of microwires EEG electrodes in a phantom. Measurements were performed at 1.5T during a high SAR TSE sequence for two different depth electrode arrangements with and without microwires. Although we observed a small temperature rise due to the presence of microwires the maximum temperature change ?T did not exceed 1°C at 1.5T. 


SAR and patient orientation for 3 T 2-channel parallel transmit pelvis imaging
Mariya Lazebnik1
1GE Healthcare, Waukesha, WI, United States
This work investigates the impact of patient orientation on SAR for 3 Tesla two-channel parallel transmit (pTx) pelvis imaging. SAR simulations were performed on two human body models in a supine position in a 70 cm-diameter 3 T body coil in a pelvis landmark, in both “head first” and “feet first” patient entry orientations. Whole body SAR, peak spatial SAR, and SAR ratio (= peak SAR / whole body SAR) were computed for quadrature and pTx excitations. Patient position and orientation can cause peak SAR and SAR ratio to vary significantly and must be considered when evaluating pTx excitation.


Subject-specific SAR prediction in adults and children at 7.0T
Gianluigi Tiberi1,2, Mauro Costagli1,2, Laura Biagi2, Alessio De Ciantis3, Nunzia Fontana4, Riccardo Stara5,6, Mark R Symms7, Mirco Cosottini8, Renzo Guerrini3, and Michela Tosetti1,2
1Imago7, Pisa, Italy, 2IRCCS Stella Maris Foundation, Pisa, Italy, 3Meyer Children’s Hospital, Firenze, Italy, 4Dipartimento di Ingegneria dell'Informazione, Pisa, Italy, 5National Institute of Nuclear Physics (INFN), Pisa, Italy, 6Stanford University, Stanford, CA, United States, 7General Electric ASL Scientist (EMEA), Pisa, Italy, 8Department of Translational Research and New Surgical and Medical Technologies, Pisa, Italy
In this study we propose a procedure which allows the prediction of global and local subject-specific SAR exposure for commonly used 7.0T sequences. Prerequisites for such prediction are: sequences’ SAR exposure simulated on the generic anatomic models; subject-specific measured B1+ maps. Validation has been provided through phantom experiment. We observed that: SILENT and FLAIR can be safely used in all subjects, both adults and children; FLAIR is more SAR demanding than SILENT; predicted SAR exposure does not show a significant variation with subject weight.


Safety of MR Imaging of Patients with Cardiac Implanted Devices
El-Sayed H. Ibrahim1, Laura Horwood1, Jadranka Stojanovska1, Luba Frank1, Anil Attili1, Hakan Oral1, and Frank Bogun1
1University of Michigan, Ann Arbor, MI, United States
This study examines whether MRI is safe in patients with cardiac implantable electronic device (CIED) excluded from published protocols, e.g. patients with abandoned leads or pacemaker dependency. A total of 162 MRI scans were obtained in 142 consecutive patients with CIED’s. Cardiac scans were performed in 94 patients and spinal/brain scans were performed in 47 patients. Only one patient developed ventricular tachycardia during a spine scan and was removed from the scanner for device reactivation without consequences. No other adverse events were noted. The devices interrogated parameters essentially remained the same immediately, 1-week after, and 3-months after the scans. 


The Potential for Eddy Current Induced Peripheral Nerve Stimulation from an Active Implanted Device Canister
Xin Chen1, Jonathan Edmonson2, and Michael Steckner1
1Toshiba Medical Research Institute USA, Inc., Mayfield Village, OH, United States, 2Medtronic CRHF, Mounds View, MN, United States
We used numerical simulations to investigate the potential for increased PNS likelihood with implanted device. Modeling of a gradient coil loaded with a human subject with a metallic implanted canister showed that the electric field around the device can increase by up to 3 fold, suggesting increased PNS likelihood.


Prospective Observational Post-marketing Study on the Safety of Gadoterate Meglumine - Final Results in the pediatric cohort of over 1,600 children
Yun Peng1
1Beijing Children's Hospital, Beijing, China, People's Republic of
An observational post-marketing study was conducted in 10 countries to prospectively collect safety data in adults and children who were scheduled to undergo routine Magnetic Resonance Imaging (MRI) with administration of gadoterate meglumine (Dotarem®). The incidence of Nephrogenic Systemic Fibrosis (NSF) in routine practice was assessed through specific follow-up of patients with moderate to severe renal impairment. Final results in a large pediatric sub-population of over 1,600 children showed a very good safety profile of gadoterate meglumine with only one adverse event reported in a child and no suspicion of NSF reported.


Scanner-specific verification of Transmit RF Body Coil B1-field to inform clinical triage of patients with implanted devices
Chi Ma1, Krzysztof R Gorny1, Christopher P Favazza1, Robert E Watson1, and Heidi A Edmonson1
1Radiology, Mayo Clinic, Rochester, MN, United States
Exclusion of scanning with transmit RF body coil may prohibit access to life-saving diagnoses for patients with MR-conditional implantable devices. Manufacturer provided plots of RF B1-field indicate that RF energy over the implant may be significantly reduced if the implant is kept outside of the 50-55cm long transmit RF body coil.  Scanner-specific B1-field measurements and RF-induced heating measurements confirm reduction in heating as conductive material moves away from scanner isocenter.  B1-field measurements lateral to the central scanner axis demonstrate local peaks in the B1-field that would not be identified from the IEC-required manufacturer plots.


Magnetic Displacement Force and Safety of Coronary Artery Stents at 7 Tesla.
Christian Hamilton-Craig1,2, Jess Cameron1, Gregory Brown1, and Graham Galloway1,3
1Centre for Advanced Imaging, University of Queensland, Brisbane, Australia, 2Richard Slaughter Centre of Excellence in CVMRI, The Prince Charles Hospital, Brisbane, Australia, 3Translational Research Institute, Brisbane, Australia
Currently, there are minimal data regarding the magnetically induced displacement force of coronary artery stents, in 7.0 T MR.  We tested a range of commonly implanted coronary artery stents for maximal displacement force at 7T.  CoCr stents appear to have safe deflection properties at 7T. However 316L-SS and PtCr stents exhibit increased magnetically induced displacement forces, and may be not be considered conditionally safe at 7.0T


Electrocorticography grids might cause excessive heating during MR imaging
Emad Ahmadi1, Reza Atefi1, Emad Eskandar2, Alexandra J. Golby3, Michael H. Lev1, Rajiv Gupta1, and Giorgio Bonmassar1
1Radiology, Massachusetts General Hospital, Boston, MA, United States, 2Neurosurgery, Massachusetts General Hospital, Boston, MA, United States, 3Neurosurgery, Brigham and Women's Hospital, Boston, MA, United States
Electrocorticography grids are routinely implanted over the cortex for pre-surgical planning in epilepsy surgery. We propose that MR imaging at 3T might cause heating injury in patients  with implanted electrocorticography grids.


Sugar free tissue-mimicking MRI phantoms for improved signal-to-noise ratio
Carlotta Ianniello1,2, Ryan Brown1, Martijn Cloos3, Qi Duan4, Jerzy Walczyk3, Graham Wiggins3, Daniel K Sodickson2,3, and Riccardo Lattanzi2,3
1Radiology, Center for Advanced Imaging Innovation and Research (CAI2R) and Center for Biomedical Imaging, Department of Radiology, New York University School of Medicine, New York, NY, United States, 2The Sackler Institute of Graduate Biomedical Science, New York University School of Medicine, New York, NY, United States, 3Center for Advanced Imaging Innovation and Research (CAI2R) and Center for Biomedical Imaging, Department of Radiology, New York University School of Medicine, New York, NY, United States, 4Laboratory of Functional and Molecular Imaging, NINDS, National Institutes of Health, Bethesda, MD, United States
We investigated Polyvinylpyrrolidone (PVP) as an alternative to sugar to control relative permittivity in tissue-mimicking MR phantoms. We constructed a two-compartment phantom filled with water solutions of PVP and NaCl, the latter used to control conductivity. A lower amount of PVP than sugar is required, allowing low permittivity materials to be realized. While signal decreases rapidly in sugar-based phantoms, PVP materials have long T2*/T2, making PVP-based phantoms suitable for the validation of MR-based electrical properties mapping techniques that rely on high SNR of signal and B1+ maps. PVP solutions are relatively inexpensive, easy to mix and do not require preservatives. 


Experimental evaluation of heating and SAR reduction with a dielectric insert at 3T
Christopher Sica1, Sebastian Rupprecht1, and Qing X Yang1
1Radiology, Penn State College of Medicine, Hershey, PA, United States
Prior work has suggested that a dielectric insert can reduce the SAR in the brain at 3T. These previous results were obtained via electromagnetic simulations. Here, we present an experimental evaluation of SAR reduction in a phantom with a dielectric insert.

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