ISMRM 23rd Annual Meeting & Exhibition • 30 May - 05 June 2015 • Toronto, Ontario, Canada

Traditional Poster Session • MR Safety: Safety & Bioeffects
1848 -1876 Safety in MRI

Safety in MRI
Tuesday 2 June 2015
Exhibition Hall 16:00 - 18:00

1848.   Use of a NURBS-Based, Full-Body Anatomy and FEA Model to Evaluate RF-Induced Heating during MR Imaging
Alan Leewood1, Sharath Gopal1, Kerim Genc2, Steve Cockram3, Philippe Young3, Jeff Crompton4, and Josh Thomas4
1MED Institute, Inc., West Lafayette, IN, United States, 2Simpleware Ltd, VA, United States, 3Simpleware Ltd, Devon, United Kingdom, 4AltaSim Technologies, LLC, OH, United States

A full-body human anatomy and multiphysics finite element analysis (FEA) model is developed to evaluate RF-induced heating from MR imaging. The FEA approach provides a coupled transient thermal solution and incorporates high fidelity geometric features at minimal computational cost, thereby overcoming two significant limitations of the finite difference time domain (FDTD) method. Specific absorption rates (SAR) from the study are in good agreement with published results based on the FDTD method; maximum temperature occurs at a location that is consistent with previous simulation and experimental results. This work will be extended to add passive implants (e.g. stents and orthopedic devices) into the anatomy.

1849.   Rapid SAR assessment of electrically thin implantable devices using an analytical approach: Proof-of-Principle for RF heating of coronary stents at 7.0 T
Lukas Winter1, Eva Oberacker1, Celal Özerdem1, Yiyi Ji1, Florian von Knobelsdorff-Brenkenhoff1,2, Gerd Weidemann3, Frank Seifert3, and Thoralf Niendorf1,2
1Berlin Ultrahigh Field Facility (B.U.F.F.), Max-Delbrück Center for Molecular Medicine, Berlin, Germany, 2Experimental and Clinical Research Center (ECRC), a joint cooperation between the Charité and the Max-Delbrueck Center for Molecular Medicine, Berlin, Germany, 3Physikalisch Technische Bundesanstalt (PTB), Braunschweig and Berlin, Germany

En route to broader clinical UHF-MR studies it is essential to gain a better insight into the interaction of passive conducting implants with radiofrequency fields. The conclusions drawn from earlier studies are valuable but constrained to the very specific experimental setup used. Recognizing the need for an universal and rapid approach for SAR assessment, this work derives and validates an analytical expression for fast SAR estimation of coronary stents. Our findings can potentially be translated to any patient, coronary stent type, RF coil configuration and RF transmission regime.

1850.   On the Subjective Acceptance during Cardiovascular Magnetic Resonance Imaging at 7.0 Tesla
Sabrina Klix1, Antje Els1, Katharina Paul1, Andreas Graessl1, Celal Oezerdem1, Oliver Weinberger1, Lukas Winter1, Christof Thalhammer1, Till Huelnhagen1, Jan Rieger1, Heidrun Mehling2, Jeanette Schulz-Menger2,3, and Thoralf Niendorf1,2
1Berlin Ultrahigh Field Facility (B.U.F.F.), Max Delbrück Center for Molecular Medicine (MDC), Berlin, Germany, 2) Experimental and Clinical Research Center (ECRC), a joint cooperation between the Charité Medical Faculty and the Max-Delbrueck-Center, Berlin, Germany, 3HELIOS Klinikum Berlin-Buch, Dept. of Cardiology and Nephrology, Berlin, Germany

This study examines the subjective acceptance during UHF-CMR in a cohort of healthy volunteers who underwent a cardiac MR examination at 7.0T.

1851.   Derived MRI induced Maximum Torque (ASTM F2213) from measured MRI induced Maximum Force (per ASTM F2052)
Richard Williamson1, Michael Childers1, Tushar Dharampal1, Shiloh Sison1, Amber Durica1, Gabriel Mouchawar1, and John Nyenhuis2
1St. Jude Medical, Sylmar, California, United States, 2Purdue University, West Lafayette, Indiana, United States

This abstract demonstrates that for some implantable devices, torque testing per ASTM F2213 as a part of MR conditional safety assessment, may not be necessary as a conservative magnetic torque value may be calculated using the measured magnetically induced force per ASTM F2052 along with the physical properties of the device. Two conservative upper-bound equations (Tier 1 and Tier 2) are derived and used to estimate the magnetically induced torque for four implantable devices.

1852.   RF current measurements in implanted wires in phantoms by fiber optic current clamps
Gerd Weidemann1, Frank Seifert1, Werner Hoffmann1, and Bernd Ittermann1
1Physikalisch-Technische Bundesanstalt, Braunschweig und Berlin, Germany

A toroidal time domain current clamp with fiber optic readout was developed for the measurement of the RF currents induced by MR investigations in the protruding ends of implanted conductive structures with diameters up to 10 mm in situ in an MR scanner. Tests with wires inside a body phantom show that even when all parts of the wires are 30 cm outside the body coil of a 3T MR scanner currents of up to 0.1 A are measured at 1 kW transmitter power.

1853.   Quantitative MR System Evaluation Using the KRMP-4 Phantom - Comparison with the ACR Phantom
Jong-Min Kim1, Jang-Gyu Cha2, Ji-Young Hwang3, Seung-Eun Jung4, Hyunn-Kyoon Lim5, Do-wan Kim6, Kwang-Su Kim6, Sung-Jin Kang2, Han-Joong Kim1, Suchit Kumar1, Junyong Park7, Chulhyun Lee7, and Chang-Hyun Oh1
1Electronic and information engineering, Korea University, Seongbuk-Gu, Seoul, Korea, 2Department of Radiology, Soonchunhyang University Bucheon Hospital, Seoul, Korea,3Department of Radiology, Ewha Women's University Mokdong Hospital, Seoul, Korea, 4Department of Radiology, The Catholic University of Korea St. Mary's Hospital, Seoul, Korea,5Korea Research Institute of Standards and Science, Daejeon, Korea, 6Korean Institute of Accreditation of Medical Imaging, Seoul, Korea, 7The MRI Team, Korea Basic Science Institute, Chungcheongbuk-do, Korea

The quality evaluation schemes such as the ACR methods1 are good enough to decide whether the MRI system is useful for clinical application based on certain measurement parameters showing the image quality. In ACR method, 11 slices of MR images are usually acquired on the ACR phantom and they are used to evaluate the 7 items (geometric accuracy, high-contrast spatial resolution, slice thickness accuracy, slice position accuracy, image intensity uniformity, percent-signal ghosting, and low-contrast object detectability). However, there are several limitations of ACR method like observer-dependent, time consuming, and accurate numerical ratings on the system performance. In this study, 3 items (vessel conspicuity, brain tissue contrast, SNR) in addition to ACR method is proposed. For semi-automatic and quantitative MR system classification, all of above-mentioned items are evaluated numerically by using MATLAB (Mathwork, Inc., MA).

1854.   RF Heating on a Vagus Nerve Stimulation Device during Head Imaging in a 3T Transmit Body Coil using a Numerical Analysis
Mélina Bouldi1,2, Olivier David1,2, Stephan Chabardes2,3, Alexandre Krainik2,3, and Jan M Warnking1,2
1Université Grenoble Alpes, Grenoble Institut des Neurosciences, Grenoble, Rhône-Alpes, France, 2U836, Inserm, Grenoble, Rhône-Alpes, France, 3CHU de Grenoble, Rhône-Alpes, France

The MR safety of a vagus nerve stimulator was assessed. Phantom experiments with a 3T whole-body transmit coil showed heating by >3K at the electrodes. E-field maps from electromagnetic simulations without the device show prominent hot spots close to the path of the VNS electrode, both in phantom and realistic human body models. This configuration, not recommended by the device manufacturer, indeed presents a significant risk, with predicted high variability of actual heating in patients dependent on the exact position of the electrode at E-field hot-spots. Simulations may be able to assess risks better than phantom experiments in this context.

1855.   Local SAR Estimation via Electrical Properties Tomography: Physical Phantom Validations at 7T
Xiaotong Zhang1, Jiaen Liu1, Pierre-Francois Van de Moortele2, and Bin He1,3
1Department of Biomedical Engineering, University of Minnesota, Minneapolis, Minnesota, United States, 2Center for Magnetic Resonance Research, University of Minnesota, Minneapolis, Minnesota, United States, 3Institute for Engineering in Medicine, University of Minnesota, Minneapolis, Minnesota, United States

Electrical Properties Tomography technique, which utilizes measurable B1 fields to reconstruct the local electrical properties of biological tissues, can be used to estimate local SAR on a subject-specific basis. The purpose of the present work is to validate such B1-based local SAR estimation by using previously proposed gEPT algorithm. B1 measurement was obtained in phantoms containing gelatin and biological tissues at 7T with a multi-channel transmit/receive coil, and local SAR distribution was predicted for a specific heating protocol. SAR results were subsequently converted into temperature changes which in turn were validated against temperature changes measured by MRI Thermometry.

1856.   Retrospective Analysis of Data in RF Heating Tests of Small Passive Medical Implants
Ting Song1, Maria Ida Iacono1, Leonardo M. Angelone1, and Sunder Rajan1
1Center for Devices and Radiological Health, U.S. Food and Drug Administration, Silver Spring, MD, United States

The purpose of this study is to perform a retrospective analysis of data related to RF-induced heating tests of medical implants provided in U.S. FDA submissions. We report interim data on 55 small passive medical implants for 1.5T and 3.0T. The data show that there is no clear length dependence for devices ¡Ü120 mm even when the data are stratified by the magnetic field, device type, and test vendor. Most devices less than 50 mm in length showed less than 2.6 oC of temperature change per WB-SAR except for one device that showed 4.5 oC of temperature change per WB-SAR.

1857.   Heating of lead electrodes disconnected from sacral stimulator during routine lumbar and pelvic MRI at 1.5T with receive-only coil
Pallab K Bhattacharyya1, Howard Goldman2, Mark J Lowe1, Adrienne Quirouet2, and Stephen E Jones1
1Imaging Institute, Cleveland Clinic, Cleveland, OH, United States, 2Glickman Urological Institute, Cleveland Clinic, Cleveland, OH, United States

RF heating testing during pelvic and lumbar scans of Medtronic Interstim II (Model 3058) implantable pulse generator (IPG) connected to Medtronic Quadipolar Nerve Stimulator Lead (Model 3889) at 1.5T Siemens Aera scanner with receive-only coils were 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.

1858.   Quantification of Ultrasonic Motor Behaviour in MRI
Peyman Shokrollahi1, Wendong Wang2, Adam C. Waspe3, James M. Drake3, and Andrew A. Goldenberg1
1Institute of Biomaterials and Biomedical Engineering, University of Toronto, Toronto, ON, Canada, 2School of Mechanical Engineering, Northwestern Polytechnical University, Xi'an, Shaanxi, China, 3Hospital for Sick Children, Toronto, ON, Canada

Obtaining haptic information and controlling the force produced by actuators is one of the key issues in performing a successful operation by surgical robots. The behaviour of MRI-compatible actuators such as ultrasonic motors (USM) in an MR environment needs to be characterized. A one DoF MR-compatible robot was built to measure the torque produced by a USM. The axial force was measured with a piezo-resistive sensor through transferring the torque using a screw. Inside and outside MR-environment forces were compared through statistical analysis. The measured force was almost doubled while the motor was running during the MR scan.

1859.   Optical E-Field Measurements in the MR Environment with High Spatial Resolution
Simon Reiß1, Andreas Bitzer2, and Michael Bock1
1Radiology - Medical Physics, University Medical Center Freiburg, Freiburg, Germany, 2Biolab Technology AG, Zürich, Switzerland

The accurate and localized measurement of electric fields in MRI is very important to assess RF safety hazards. In this work we present a purely optical sensor which is substantially smaller than existing dipoles to measure E-fields with high spatial resolution in a clinical MR system. This sensor allows for MR-safety inspections of RF coils and even for E-field assessment of small metallic structures such as implants or catheters in the MRI environment.

1860.   Correlation of improved local SAR deposition with reduced shading close to hip implants
Thomas Lottner1,2, Mathias Nittka1, Theresa Bachschmidt1,3, Heiko Meyer1, and Wolfgang Nitz1,2
1Siemens Healthcare, Erlangen, Germany, 2University of Regensburg, Regensburg, Germany, 3Experimental Physics 5, University of Würzburg, Würzburg, Germany

Changing the B1 polarization has shown to reduce artifacts due to induced currents in metallic implants. The presented work aims to show that the right elliptical polarization not just improves image quality, but furthermore decrease the SAR value near the implant. Numerical simulations were performed on a human male with a simplified implant model placed in his right femoral bone. The optimal polarization was approximated by an analytical model. The optimized and the circular polarization were compared and a significant increase of B1 homogeneity and decrease in local SAR was shown for the elliptical polarization.

1861.   MR safety investigation of RF heating of a generic wire-shaped device immersed to a human body simulating medium at 63.58 MHz (1.5 T MRI-equivalent)
Mahdi Abbasi1,2, Gregor Schaefers1, Amin Douiri1, and Daniel Erni2
1MR:comp GmbH, Gelsenkirchen, NRW, Germany, 2General and Theoretical Electrical Engineering (ATE), University of Duisburg-Essen, Duisburg, NRW, Germany

The quantitative analysis of induced E-field due to presence of medical catheter implants during MRI become particularly critical if the implant is only semi immersed into the human body where a part remains outside. As examples, deep brain electrodes are partly immersed into the brain and various EEG and ECG electrodes as zero immersing configurations. As the result of the numerical simulations, SAR distribution in the surroundings of the tip of the generic implants is obtained for 3 configurations under test: partly immersed insulated/uninsulated and fully immersed uninsulated generic implant. Temperature measurements are done for all worst case lengths and two adjacent lengths in an in-house 64 MHz RF laboratory system.

1862.   Mathematical Tools to Define SAR Margins for Phased Array Coil In-Vivo Applications Given E-field Uncertainties
Guillaume Ferrand1, Michel Luong1, Alexis Amadon2, and Nicolas Boulant2
1DSM/IRFU/SACM, CEA-Saclay, Gif-sur-Yvette, France, 2DSV/I2BM/Neurospin, CEA-Saclay, Gif-sur-Yvette, France

In high field MRI, a phased array coil comprising a large number of transmit elements appears more attractive with regard to local SAR reduction and to RF inhomogeneity mitigation. However, the linear combination of electric fields errors makes the total SAR error much more complex to estimate. Here, we propose mathematical tools and hypotheses to estimate the standard deviation of the SAR produced by multiple transmit elements, knowing the standard deviation of the error on the electrical field produced by each element. Thanks to these tools, the best margins can be applied to the final SAR, to ensure the safety of the patient in in-vivo experiments, without overconservative measures.

1863.   Effect of anisotropy on the accuracy of quantitative conductivity imaging. A numerical study
Nahla M H Elsaid1, Adrian I Nachman2,3, Weijing Ma2, Tim P DeMonte4, and Michael L G Joy1,2
1IBBME, University of Toronto, Toronto, Ontario, Canada, 2Electrical and Computer Engineering, University of Toronto, Toronto, Ontario, Canada, 3Department of Mathematics, University of Toronto, Toronto, Ontario, Canada, 4FieldMetrica Inc., Toronto, Ontario, Canada

This is a numerical study showing the effect of anisotropy on the accuracy of conductivity values from two different types of conductivity imaging methods. One is anisotropic based method versus another that is isotropic based. The comparison is made using a validation approach that requires a forward solver which imports the anisotropic conductivity or the isotropic conductivity according to the method to be validated.

1864.   RF safety assessment of simultaneous EEG-fMRI at 7T MR
Özlem Ipek1, Joao Jorge2,3, Frederic Grouiller4, Wietske van der Zwaag1, Lijing Xin2, and Rolf Gruetter2,5
1CIBM-AIT, EPFL, Lausanne, Vaud, Switzerland, 2LIFMET, EPFL, Lausanne, Vaud, Switzerland, 3Bioengineering, University of Lisbon, Lisbon, Portugal, 4CIBM, Geneva University Hospital, Geneva, Switzerland, 5Radiology, University of Lausanne, Lausanne, Vaud, Switzerland

An exact model of a 64-channel EEG cap and the RF-coil was simulated, and B1+ and SAR distributions across the human head evaluated with/without the presence of the EEG cap. Simulation results were complemented by experimental B1+ and temperature measurements from a human subject with simultaneous EEG acquisition, using both RF volume and surface coils at 7T MR. No RF-safety concern is raised for simultaneous EEG-fMRI at 7T MR with the current setup. However, with the introduction of the EEG cap, a pronounced RF shielding effect is found, which leads to a decrease in the RF efficiency in the subject.

1865.   A method for the measurement of the RF power radiated by 7T transmit coils
Gerd Weidemann1, Frank Seifert1, Werner Hoffmann1, Harald Pfeiffer1, and Bernd Ittermann1
1Physikalisch-Technische Bundesanstalt, Braunschweig und Berlin, Germany

A method to derive the radiated power of 7T transmit coils is developed and applied to an 8-channel pTx coil to determine the radiated power as a function of steering conditions. It is based on fiber optic time domain E-field vector measurements inside a cylindrical single mode waveguide which mimics the patient tunnel of a typical 7T scanner. The maximum radiated power was found for the CP-mode of the array coil. Although, the portion of the radiated power of the specific coil studied is low it can be higher for other coil designs and will become more prominent for higher fields.

1866.   Ultra High Resolution 3D Gradient Recalled Echo With Reduced FOV Spiral Selective Excitation.
Malek I. Makki1
1MRI Research, University Children Hospital Zurich, Zurich, Switzerland

Inward spiral-trajectory technique was used as slice-select excitation to acquire reduced FOV volumetric 3D fast gradient recalled echo and achieve ultra-high spatio-temporal resolution images at high SNR and free of blurring artefact.

1867.   Hearing Loss in Dogs After Routine Neurological MRIs
Rebecca Krimins1,2, Larry Gainsburg3, Amanda Lauer4, Meiyappan Solaiyappan2, and Dara Kraitchman1,2
1Center for Image-Guided Animal Therapy, Johns Hopkins University, Baltimore, Maryland, United States, 2Russell H. Morgan Department of Radiology and Radiological Science, Johns Hopkins University, Baltimore, Maryland, United States, 3Mid-Atlantic Veterinary Neurology and Neurosurgery, Catonsville, Maryland, United States, 4Department of Otolaryngology and Center for Hearing and Balance, Johns Hopkins University, Baltimore, Maryland, United States

The auditory brainstem response test is the accepted test for detecting hearing loss in dogs. Current standards in veterinary medicine do not require hearing protection for canines undergoing MRI. The purpose of this study was to determine whether routine MRI studies at 1.5T cause hearing loss in client-owned dogs. In addition, the authors assessed whether or not hearing protection can be beneficial.

1868.   Improved MR thermometry in the presence of non-water proton signals
Jacco A de Zwart1, Peter van Gelderen1, Qi Duan1, Natalia Gudino1, Cem M Deniz2, Leeor Alon2, and Jeff H Duyn1
1Advanced MRI, LFMI, NINDS, National Institutes of Health, Bethesda, MD, United States, 2Dept. of Radiology & Sackler Institute of Graduate Biomedical Sciences, NYU School of Medicine, New York, NY, United States

A non-linear least squares fitting based method for MR thermometry is proposed and developed for coil performance and RF-safety assessment using recently developed sucrose-doped agarose-water phantoms. The method, which acquires a minimum of four gradient-echo signals, allows reliable measurement of RF-heating-related shifts in water proton resonance frequency (PRF) in the presence of confounding proton signals from the doping material. Calibration experiments show water-PRF temperature dependence of -0.009 ppm·K-1 for these agarose-based phantoms, similar to literature values for tissue (~-0.01 ppm·K-1). However, otherwise identical gelatin-based gels show reduced water-PRF temperature dependence (-0.006 ppm·K-1), possibly due to spin exchange.

1869.   Are MR Manufacturer-Reported Specific Absorption Rate Values on Clinical MRI systems correct?
Youngseob Seo1 and Min-Jae Kang1
1Center for Medical Metrology, Korea Research Institute of Standards and Science, Daejeon, Korea

MR manufacturer-reported specific absorption rate (SAR) values on clinical MR imaging systems are uncertain. Radiofrequency heating during MRI scan is an important safety concern. We measured SAR values and temperature elevation at 1.5 and 3 T.

1870.   Spatially Localized Tissue Fingerprinting (STiF)
Shivaprasad Ashok Chikop1, Antharikshanagar Bellappa Sachin Anchan1, Arush Arun Honnedevasthana1, Shaikh Imam1, and Sairam Geethanath1
1Medical Imaging Research Center, Dayananda Sagar Institutions, Bangalore, Karnataka, India

Spatially localized Tissue Fingerprinting (STiF) provides Non-MR parametric maps (NPM) based on tissue properties like electrical conductivity, thermal conductivity, tissue density, heat capacity, elasticity and heat generation rate. These maps reflect structural, functional and pathological conditions of the tissues and they can be used for SAR calculation in EM modeling and analysis which are based on tissue types. StiF relates MR data with NPM through Magnetic Resonance Fingerprinting so as to map a range of MR parameters to a range of non-MR parameters via tissue characteristics, similar to MRF which maps signal evolution to MR parametric maps.

1871.   Reducing the peak SAR surrounding implanted lead tips in 3T MRI using a high-dielectric helmet former: a numerical feasibility study
Zidan Yu1, Sherman Xuegang Xin1,2, and Christopher Collins1
1Bernard and Irene Schwartz Center for Biomedical Imaging, New York University School of Medicine, New York, New York, United States, 2Biomedical Engineering, Southern Medical University, Guangzhou, Guangdong, China

Due to the high likelihood for a patient implanted with a pacemaker to take an MRI exam, and the significant concern about the SAR around the lead tip of an implanted pacemaker, the feasibility of employing high permittivity materials for reducing the SAR is explored here. The results indicated that it is promising to reduce heating around the lead tip with use of dielectric materials in a situation where a patient with an implanted pacemaker undergoes an MR scan of head and a large birdcage coil is used in transmission but a local receive coil is used in reception.

1872.   Globally Applicable MR Safety Program for Medical Students
Steffen Sammet1,2 and Christina Louise Sammet3,4
1Department of Radiology, University of Chicago Medical Center, Chicago, Illinois, United States, 2Department of Radiology, The Ohio State University, Columbus, Ohio, United States,3Department of Radiology, Ann & Robert H. Lurie Children’s Hospital of Chicago, Chicago, Illinois, United States, 4Department of Radiology, Northwestern University, Chicago, Illinois, United States

This educational electronic poster outlines the design of a globally applicable educational MR safety module with a concise multiple-choice exam for instructing medical students about basic MR and patient related safety. The MR safety course can be implemented as a traditional didactic lecture, interactive, or self-administered online. The goal of the course is to make sure that medical students worldwide get a basic understanding of MR principles and safety considerations. It can be used universally by all medical school programs and will help to ensure consistent quality of teaching materials and MR safety standards.

1873.   Faster B1 Field and SAR Estimation in Parallel Transmit Arrays without Tuning using Voltage Sources
Hongbae Jeong1, Konstantinos Papoutsis1, Peter Jezzard1, and Aaron T. Hess2
1FMRIB Centre, University of Oxford, Oxford, Oxfordshire, United Kingdom, 2Department of Cardiovascular Medicine, University of Oxford, Oxford, Oxfordshire, United Kingdom

In ultra-high-field magnetic resonance imaging, there are two specific needs for EM simulation: one is the estimation of transmit and receive magnetic field distributions and the other is the estimation of specific absorption rate. In this study, we compare and evaluate two methods of simulating an eight channel parallel transmit transceiver coil via generated B1+ fields and SAR distribution in a 7T cylindrical phantom and human head model. Method 1 is the conventional tuning method whereby one voltage source is placed on each element and manually tuned using explicit capacitor values and Method 2 only uses voltage sources.

1874.   MRI in patients with cardiac implantable electronic devices, our institutional experience
Iva Petkovska1, Bobby Kalb1, John Hur1, Peter Ott2, Kusum Lata2, Parinita Dherange2, Isabel Oliva1, Shannon Urbina1, Hina Arif1, Surya Chundru1, James Costello1, and Diego Martin1
1Medical Imaging, University of Arizona, Tucson, AZ, United States, 2Sarver Heart Center, University of Arizona, Tucson, AZ, United States

MRI in patients with cardiac implantable electronic devices could be performed safely on a case-by-case basis and only if the site is staffed with individuals with the appropriate radiology and cardiology knowledge and expertise, including cases involving directed cardiothoracic imaging.

1875.   Is Pacemaker Lead-Tip Heating Greater at 1.5T or 3T?
Deborah Anne Langman1, Eric Aliotta1,2, Dan Margolis1, J. Paul Finn1,2, and Daniel B Ennis1,2
1Radiological Sciences, UCLA, Los Angeles, CA, United States, 2Biomedical Physics IDP, UCLA, Los Angeles, CA, United States

3T MRI exams for patients with pacemakers and ICDs is contraindicated, largely due to concerns that lead-tip heating is worse at 3T. Our objective was to characterize in vitro pacemaker lead-tip heating during a range of 3T MRI exams compared to 1.5T. 3T lead-tip heating was found to be lower than 1.5T lead-tip heating near the center of the B1-coil and higher near the periphery, whereas for 1.5T the highest heating was near the center of the B1-coil. Our reluctance to scan patients with pacemakers or ICDs at 3T may be misguided under some conditions and deserves greater consideration.

1876.   RF Safety Evaluation of a Breast Expander Implant at 3.0T
BuSik Park1, Amir Razjouyan2, Leonardo Angelone2, and Sunder s Rajan3
1FDA/CBER, Silver Spring, MD, United States, 2FDA/CDRH/OSEL, MD, United States, 3Div. of Biomedical Physics, FDA/CDRH, Silver Spring, MD, United States

We present numerical simulations at 128 MHz of specific absorption rate (SAR) in a virtual female model with a breast expander implant. The analysis was performed using four different body positions landmarked to isocenter (i.e., shoulder, heart, sternum, and abdomen). The 10g-averaged SAR (SAR10g) with and without the breast expander implant was evaluated at selected coronal planes (i.e., center of the implant and 37.5 mm above). The simulation results showed that the highest SAR10g changes with the breast expander implant were in the saline volume of the implant. The SAR10g within the implant decreased, compared to background whereas it increased in some of the surrounding regions of the implant. However, the maximum SAR10g (SAR10g-peak) in a selected region of interest (ROI) around the implant was still less compared to the peak value over the entire body (i.e., 26.0 W/kg vs. 41.2 W/kg), indicating no significant effect of the implant on the overall ratio SAR10g-peak/whole-body averaged SAR.