Eugenia Cabot¹, Earl Zastrow^1,2, and Niels Kuster^1,2
1IT'IS Foundation, Zurich, Switzerland, ²ETHZ, Zurich, Switzerland

A study of in vivo radiofrequency exposure of a group of human models to a reduced set of birdcages that cover clinical scanner variability was performed at 64 MHz, with a view to the assessment of implant safety during magnetic resonance imaging. Finite-difference time-domain simulations were run for combinations of human model/landmark/birdcage for quadrature fed coils representing closed-bore systems with respect to RF exposure. The evaluation of the E-fields for the Tier 3 of TS10974¹ shows large variations in the tangential E-field values obtained with the different coils.

Mahdi Abbasi^1,2, Yacine Noureddine¹, Gregor Schaefers^1,3, and Daniel Erni^2
1MR:comp GmbH, Gelsenkirchen, Germany, ²Faculty of Engineering/ATE, Duisburg-Essen University, Duisburg, Germany, ³MRI-STaR GmbH, Gelsenkirchen, Germany

comparison study has been implemented for a generic orthopedic implant (GOI) in ASTM and Elliptical phantom as well as in homogeneous and heterogeneous Duke model in terms of RF induced heating to evaluate the uncertainty of RF induced heating tests in phantoms. The parameters to be evaluated to track the hotspots at the surrounding tissue of the GOI were assessed.

Arian Beqiri¹, Joseph V Hajnal^1,2, and Shaihan J Malik^1
1Imaging Sciences and Biomedical Engineering, King's College London, London, United Kingdom, ²Centre for the Developing Brain, King's College London, London, United Kingdom

Ensuring safe imaging around metallic implants is paramount to safety in MRI. Parallel transmission offers the possibility of electromagnetically decoupling metallic implants from an RF coil. Here the impact of the number of transmit channels used is assessed in terms of reduction of SAR around the implant and improvement in the homogeneity of the B₁⁺ imaging field.

Volkan Acikel¹ and Daniel B Ennis^1,2
1Department of Radiological Sciences, University of California Los Angeles, Los Angeles, CA, United States, ²Department of Bioengineering, University of California Los Angeles, Los Angeles, CA, United States

MRI presents several potential risks for patients with implanted devices and one of the main concerns is RF induced heating of devices and nearby tissues.  The aim of this study was to compare the RF induced heating characteristic of wires at 1.5T and 3T using simulations and direct measurements. Greater heating (SAR amplification) can be observed at lower field strengths for longer wires.

Mahsa Fatahi¹, Annika Reddig², Vijayalaxmi Vijayalaxmi³, Bjoern Friebe⁴, Dirk Roggenbuck ^5,6, Dirk Reinhold², and Oliver Speck^1,7,8,9
1Biomedical Magnetic Resonance, Otto-von-Guericke-University Magdeburg, Magdeburg, Germany, ²Institute of Molecular and Clinical Immunology, Otto-von-Guericke-University Magdeburg, Magdeburg, Germany, ³Department of Radiology, University of Texas Health Science Center, San Antonio, TX, United States, ⁴Department of Radiology and Nuclear Medicine, Otto-von-Guericke-University Magdeburg, Magdeburg, Germany, ⁵Faculty of Natural Sciences, Brandenburg University of Technology Cottbus-Senftenberg, Senftenberg, Germany, ⁶Medipan GmbH, Dahlewitz/Berlin, Berlin, Germany, ⁷Leibniz Institute for Neurobiology, Magdeburg, Germany, ⁸Center for Behavioral Brain Sciences, Magdeburg, Germany, ⁹German Center for Neurodegenerative Disease, Magdeburg, Germany

Synopsis. Ultra-high field magnetic resonance imaging (UHF MRI) is a technological development which is now only used for research purpose. Healthy individuals working with UHF MRI scanners as well as those participating in research investigations are repeatedly exposed to high field strengths, which can be >2-fold greater than those regularly used in clinics. In this study, we have examined the extent of genetic damage in peripheral blood mononuclear cells (PBMC) obtained from such individuals exposed to 7T MRI.

Paul de Bruin¹, Wouter Teeuwisse¹, Andrew Webb¹, and Rolf Hut^2
1Leiden University Medical Centre, Leiden, Netherlands, ²Technical University Delft, Delft, Netherlands

A new method of monitoring temperature non-invasively within an MRI scanner is introduced. This method is based on Raman backscattering, with the sensor consisting of a long length of thin optical fibre which can be arranged in any desired geometry. The major advantage over existing techniques is that a wide area of surface temperatures can be monitored simultaneously. Preliminary feasibility of the approach is shown here for localized and global temperature measurements.

Samuel Barnes¹, Thomas Ng², and Russell Jacobs^3
1Radiology, Loma Linda University Medical Center, Loma Linda, CA, United States, ²Radiology, Brigham and Women's Hospital, Boston, MA, United States, ³Caltech, Pasadena, CA, United States

For increased patient safety it is desirable to acquire dynamic contrast enhanced (DCE) MRI data with the lowest passable Gd contrast agent (CA) dose. However, a lower CA dose generally leads to smaller signal changes and lower quality studies. Through simulations we show that lower CA doses (up to 1/2 dose) can be compensated for by extending the pre-injection baseline acquisition time to maintain similar accuracy and precision of the fitted K_trans values.

Yan Cao¹, Yang Zhang^1,2, George Shih¹, Yan Zhang¹, and Martin R Prince^1,3
1Radiology, Weill Cornell Medical Center, New York, NY, United States, ²Radiology, Qilu Hospital, Shandong University, Jinan, China, People's Republic of, ³Radiology, Columbia University, New York, NY, United States

Dialysis patients had 3 times the signal increase on unenhanced T1-weighted images compared to a control population with near normal renal function undergoing the identical number of GBCA administrations.  Although any clinical consequence to GBCA administration would be expected to be magnified in dialysis patients, no clinical effect of receiving GBCA could be identified in the nephrologist/nursing notes recorded 3 times a week in the 30 days following GBCA administration. 

Matthias Hackenbroch¹, De Hua Chang¹, and David Maintz^1
1Radiology, University Clinic of Cologne, Cologne, Germany

A non-interventional post-marketing surveillance study carried out between January 2012 and October 2013 on 1,537 patients in 15 centres showed that Dotarem® (Guerbet, Roissy, France) is an effective contrast agent for the identification of invasive ductal carcinomas. An MR mammography with the diagnosis of invasive ductal carcinoma was confirmed in 93.5% of all cases by means of a subsequent cytological examination. Overall, a diagnosis was able to be made in 99.2% of the cases. Adverse reactions occurred in 5 patients (0.3%). In 4 out of 5 of the patients the adverse events were not serious and in one patient the adverse events were serious.

Huan Li¹, Chao Jin¹, Jianxin Guo¹, Miaomiao Wang¹, and Jian Yang^1
1Department of Radiology, the First Affiliated Hospital of Xi’an Jiaotong University, Xi'an, China, People's Republic of

The temporary or permanent effects of strong noise from MRI devices on hearing functions, especially for different age populations (e.g. neonate and adult) remain unclear. Here we conduct a longitudinal study targeting 3T MRI to disclose such effects on hearing functions of young adults and neonates. Results indicate that due to immaturity of hearing nerve system, neonates show weaker sensitivity to acoustic noise than adults. The 3T MRI noise resulted in transient decrease of young adults’ hearing function (i.e. temporary threshold shift), whereas showed rarely effects on neonates.

Ihsan Zainul¹, Mahdi Abbasi^1,2, and Gregor Schaefers^1,3
1MR:comp GmbH, Gelsenkirchen, Germany, ²Faculty of Engineering/ATE, Duisburg-Essen University, Duisburg, Germany, ³MRI-STaR GmbH, Gelsenkirchen, Germany

The interaction between the gradient induced eddy current and the static magnetic field in the MRI system generates force and torque to a conductive implant if the eddy current magnetic moment and static magnetic field are misaligned. A frequency-domain solver (F-solver) of full-wave simulator CST studio suite 2015 was employed as an initial step to calculate the surface current induced due to the gradient field-induced switching.

Daniel J Martire¹, Krzysztof Wawrzyn¹, William Bradfield Handler¹, and Blaine A Chronik^1
1Physics and Astronomy, Western University, London, ON, Canada

In this project, a method to quantify the gradient-induced vibration of a medical device in an MR system using a laser Doppler vibrometer is presented. A copper annulus was suspended in a 3T scanner, at a position chosen to maximize the x-component of the x-gradient. The displacement of the device was measured at different gradient field strengths. Typical observations were understood, which should lead towards helping establish a test standard for gradient induced vibrations of implanted medical devices.

Joseph Vincent Rispoli^1
1Weldon School of Biomedical Engineering, Purdue University, West Lafayette, IN, United States

It is common practice to perform full-wave electromagnetic modeling to characterize RF transmit coils and establish safety parameters limiting power and SAR to comply with guidelines for pre-clinical use with human volunteers. Currently-available female voxel models are unsuitable for simulating the filling factor of breast coils designed for women in the prone position. Accurate breast modeling is further confounded by variability of lipid and fibroglandular tissues, with modeling implications owing to disparate conductivity and permittivity values. This work presents simulations at 7T using high-resolution, anatomically-correct breast phantoms exhibiting varying proportions of fatty and fibroglandular tissues, as well as breast tissue girth, length, and positioning within the RF coil, demonstrating the effects of these variables in projected SAR for breast imaging. 

Giuseppe Carluccio^1,2, Yu-Shin Ding^1,2, Jean Logan^1,2, and Christopher Michael Collins^1,2
1Radiology, Center for Advanced Imaging Innovation and Research (CAI2R), New York, NY, United States, ²Radiology, Bernard and Irene Schwartz Center for Biomedical Imaging, New York, NY, United States

We explore the possibility that SAR-related temperature increase could affect metabolic rates enough to alter FDG signal in MR/PET. Using numerical simulations, we calculate the distributions of SAR, temperature, metabolic rates, FDG concentration ([FDG]), and PET signal throughout the human body. Calculation of [FDG] utilizes a two-compartment model considering metabolic rate through time. Results are calculated for injection time one hour before the onset of imaging and for injection time simultaneous with the onset of imaging. Even for worst-case scenario (max allowable whole-body SAR for the duration of the scan), there is little observable effect on PET signal.

Arian Beqiri¹, Jeffrey W Hand¹, Joseph V Hajnal^1,2, and Shaihan J Malik^1
1Imaging Sciences and Biomedical Engineering, King's College London, London, United Kingdom, ²Centre for the Developing Brain, King's College London, London, United Kingdom

Computing 10g averaged local SAR Q-matrices for parallel transmission MRI using self-implemented code is complex and computationally expensive. Here we present a simple method for computing Q-matrices using channel combinations of 10g SAR calculated with electromagnetic field simulation software and then simply constructed into Q-matrices from these combinations.

Clare McElcheran¹, Laleh Golenstani-Rad², and Simon Graham^3
1University of Toronto, Toronto, ON, Canada, ²Massachusetts General Hospital, Charlestown, MA, United States, ³Sunnybrook Health Sciences Centre, Toronto, ON, Canada

Long implanted wires, such as deep brain stimulation (DBS) implants, are subject to radiofrequency (RF) heating during MRI.  In previous work, RF shimming was used to tailor the electric and magnetic fields creating optimal excitation and minimal heating in a uniform cylindrical medium with a single, straight, implanted copper wire at 3T.  This work extends the methodology to a complex, heterogeneous head model with one or two implanted, curved copper wire(s).  A substantial improvement in both B₁⁺-field homogeneity and E-field reduction is achieved when compared with a transmit/receive birdcage coil in both the single wire and bilateral wire case.

Ettore Flavio Meliadò¹, Alexander J.E Raaijmakers¹, Matthew C. Restivo¹, Matteo Maspero¹, Peter R. Luijten¹, and Cornelis A.T. van den Berg^1
1Center for Image Sciences, University Medical Center Utrecht, Utrecht, Netherlands

A reliable technique to assess the 10g averaged Specific Absorption Rate is necessary for parallel transmit ultra-high field body MRI. We believe that the best solution is to build a database with many different models. We have created nine dedicated body models and performed FDTD simulations on them to evaluate the inter-subject variability for prostate imaging at 7T using fractionated dipole antennas. Maximum SAR_10g ranges from 1.64 to 2.48W/kg with 8x1W input power. No relationship was found between BMI and maximum SAR_10g. Intra-subject variability (caused by slight antenna positioning variability, +/-2cm) was also investigated showing up to 67.8% SAR variability.

Fu-Hsing Wu¹, Edzer L. Wu¹, and Jyh-Horng Chen^1
1Interdisciplinary MRI/MRS Lab, Department of Electrical Engineering, National Taiwan University, Taipei, Taiwan

    The multislice RF pulse excitation is required in some simultaneous multi-slice (SMS) methods. The aim of this study was to investigate the synthesis method and SAR (Specific Absorption Rate) of multislice PINS (Power Independent of Number of Slices) SLR RF pulses for Wideband MRI and other SMS methods.

    The relative values of SAR of the standard SLR and PINS SLR RF pulses with different number of slices W are presented. It can be found that the values of SAR of PINS SLR pulses were greatly reduced compared to that of the standard SLR pulses. For example, The SAR of PINS SLR with W = 5 is only 38% of that of standard SLR with W = 5. And The SAR of PINS SLR with W = 5 is only 1.9 times of that of standard SLR with W = 1.

Xinqiang Yan^1,2, Lei Shi³, Baotong Feng², Zhe Wang¹, Shujun Wei², Chuangxi Ma², Long Wei², and Rong Xue^1
1State Key Laboratory of Brain and Cognitive Science, Beijing MRI Center for Brain Research, Institute of Biophysics, Chinese Academy of Sciences, Beijing, China, People's Republic of, ²Key Laboratory of Nuclear Radiation and Nuclear Energy Technology, Institute of High Energy Physics, Chinese Academy of Sciences, Beijing, China, People's Republic of, ³State Key Laboratory of Magnetic Resonance and Atomic and Molecular Physics, Wuhan Institute of Physics and Mathematics, Chinese Academy of Sciences, Wuhan, China, People's Republic of

Specific absorption rate (SAR) is a limiting factor for high field MRI due to excess RF power deposition in human subjects. In this study, we developed a multi-channel real-time RF power monitoring system for global and local SAR estimation using FPGA to ensure patient safety. The major components of the monitoring system include multiple dual directional couplers, demodulating logarithmic power sensors, analog to digital converters and a FPGA fast signal processing unit, etc. The deviation of the power measurement was less than 0.5dB after calibration for system errors over a dynamic RF signal range of 100dB.

Thomas M. Fiedler¹, Mark E. Ladd^1,2, and Andreas K. Bitz^1
1Medical Physics in Radiology, German Cancer Research Center (DKFZ), Heidelberg, Germany, ²Erwin L. Hahn Institute for Magnetic Resonance Imaging, University Duisburg-Essen, Essen, Germany

It has been shown that specific configurations of high-permittivity pads can lead to an increase of local SAR. So far, the effects of high-permittivity pads on RF fields have been investigated only for ¹H imaging at 7 Tesla. For X-nuclei imaging typically dual-tuned coils are applied. In this work, we investigate the effect of high-permittivity pads, typically utilized to optimize RF fields for ¹H imaging, for²³Na imaging at 7T. RF simulations were performed for two body models to determine under which conditions SAR elevations are likely to occur or can be avoided.  

Yigitcan Eryaman¹, Patrick Zhang¹, Lynn Utecht¹, Russell L Lagore¹, Arcan Erturk¹, Angel Torrado-Carvajal^2,3, Esra Abaci Turk^3,4, Lance DelaBarre¹, Gregory J. Metzger¹, and J. Thomas Vaughan^1
1CMRR,Radiology, University of Minnesota, Minneapolis, MN, United States, ²Medical Image Analysis and Biometry Laboratory, Universidad Rey Juan Carlos, Mostoles, Madrid, Spain, Madrid, Spain,³Madrid-MIT M+Vision Consortium in RLE, Massachusetts Institute of Technology, Boston, MA, United States, ⁴Boston Children's Hospital, Harvard Medical School, Boston, MA, United States

We present our results regarding electromagnetic & thermal simulations  as well as temperature measurement studies in anesthesized pigs. Pig models were generated by segmenting tissues from CT images. Fractionated dipole antennas were used to deliver RF energy in the pigs body. Power levels used for RF excitation were monitored. Temperature measurements were made using 4 fiber optic probes at locations which are visible in the digital pig model. Simulation and Experiment results were compared.

Shiloh Sison¹, Xin Huang², Shi Feng³, Ji Chen², Richard Williamson³, and Gabriel Mouchawar^3
1St. Jude Medical, Sunnyvale, CA, United States, ²University of Houston, Houston, TX, United States, ³St. Jude Medical, Sylmar, CA, United States

E-fields tangential to implantable cardiac pacemakers and defibrillators were analyzed at Normal and First Level Controlled Operating Modes as well as 30uT peak B1+. 1.5T body transmit and head and extremity transmit RF coils were simulated. A comparison of the Etans generated by the body transmit coils is made to those generated by head and extremity transmit coils. If RF heating and voltage can be shown to be safe with unrestricted body coils then no additional analysis is necessary for head and extremity coils since there is a 9x margin in RF heating and 3x margin in voltage.

Thomas M. Fiedler¹, Mark E. Ladd^1,2, and Andreas K. Bitz^1
1Medical Physics in Radiology, German Cancer Research Center (DKFZ), Heidelberg, Germany, ²Erwin L. Hahn Institute for Magnetic Resonance Imaging, University Duisburg-Essen, Essen, Germany

RF safety of Tx coils can be assessed based on SAR or temperature limits; however, temperature is directly correlated to tissue damage and enables a more precise RF exposure assessment. Both safety assessments were compared for a 7T breast coil. Temperature depends on the individual thermoregulation system and was taken into account using three different temperature-dependent blood perfusions. Results for a subject with impaired thermoregulation showed that temperature limits are exceeded by up to 6.17 °C even when SAR limits are complied with. For a healthy subject, up to 40% higher input power is allowed if temperature limits are applied instead of SAR. 

Steffen Sammet¹ and Christina Louise Sammet^2,3
1Department of Radiology, University of Chicago Medical Center, Chicago, IL, United States, ²Department of Radiology, Northwestern University, Chicago, IL, United States, ³Department of Medical Imaging, Ann & Robert H. Lurie Children’s Hospital of Chicago, Chicago, IL, United States

We propose an educational magnetic resonance (MR) safety course for instructing medical students world-wide about basic MR and patient-related safety. The MR safety course material can be implemented as a traditional didactic or interactive lecture in combination with hands-on safety demonstrations and will prepare medical students for patient screening and safety consultations when ordering MR studies. This course can be implemented globally by various medical school programs to ensure consistent quality of teaching materials and MR safety standards.