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

MR Safety
Monday 12 May 2014
Space 2  16:30 - 18:30 Moderators: Ingmar Graesslin, Dipl.-Ing., Cornelis A. T. van den Berg, Ph.D.

16:30 0172.   Radiofrequency Heating during Body Imaging in a 3T Body Coil and Patient Safety
Devashish Shrivastava1, Jinfeng Tian1, John Hughes1, and J Thomas Vaughan1
1University of Minnesota, Minneapolis, MN, United States

In vivo radiofrequency (RF) heating was simulated by solving the first principles based generic bioheat transfer model (GBHTM) in a digital pig due the power deposition from a 3T body coil. The simulations were validated by measuring the heating using fluoroptic probes in anesthetized swine due to the whole-body average power deposition of 2.77 W/kg for an hour in a 3T scanner. The GBHTM predicted the RF heating accurately. The simulations and measurements provided fundamental understanding of the RF energy transport and related heating in vivo to make MRI more powerful as well as improve patient safety.

16:42 0173.   Cerebral Tissue Contrast is Mostly Preserved in Low SAR Inversion Recovery MRI for Parkinson’s Patients with Deep Brain Stimulators
Subhendra N Sarkar1, Ron L Alterman2, Efstathios Papavassiliou2, Douglas L Teich1, Rafael Rojas1, Rafeeque A Bhadelia1, Jeremy Stormann1, Ines Cabral-Goncalves1, and David B Hackney1
1Radiology, Beth Israel Deaconess Medical Center, Harvard Medical School, BOSTON, MA, United States, 2Division of Neurosurgery, Beth Israel Deaconess Medical Center, Harvard Medical School, BOSTON, MA, United States

Treatment efficacy for deep brain stimulators (DBS) in medically refractory Parkinson’s is high when surgical planning and further assessments are done by high quality MRI with adequate RF power although there exist severe SAR restrictions for that. Sentinel events after MRI seems rare but neurologic deficits previously attributed to surgery could have been from routine MRI. We have developed and tested the utility of a modified FSTIR sequence within low SAR guidelines on patients with DBS and observed similar tissue contrasts from the low and high SAR sequences with low SAR images being equally useful for diagnosis and neurosurgical planning.

16:54 0174.   
Reduced Heating of Implanted Electrical Conductors Using Parallel Radiofrequency Transmission
Clare McElcheran1, Laleh Golestanirad2, and Simon Graham1,2
1Medical Biophysics, University of Toronto, Toronto, ON, Canada, 2Sunnybrook Health Science Centre, Toronto, ON, Canada

Deep Brain Stimulation (DBS), a treatment for movement disorders (eg Parkinson’s Disease) consists of leads and electrodes that send electrical impulses to deep brain nuclei. During MRI, the electric field (E) created by radiofrequency (RF) excitation couples with the leads, amplifies E, and can cause dangerous heating of nearby tissues. Parallel RF transmission (PTX) is investigated to suppress heating by varying the amplitude and phase of each transmit element. In an 8-element PTX with a uniform cylindrical phantom, E is reduced 97% compared to a linear birdcage transmitter, with <10% transmit magnetic field inhomogeneity in the chosen field of view.

17:06 0175.   Comprehensive RF Safety Concept for Parallel Transmission MR
Ingmar Graesslin1, Peter Vernickel1, Peter Börnert1, Kay Nehrke1, Giel Mens2, Paul Harvey2, and Ulrich Katscher1
1Philips Research Laboratories, Hamburg, Germany, 2Philips Healthcare, Best, Netherlands

Achieving RF patient safety in parallel transmission is difficult, due to the freedom in tailoring the RF transmit fields. Before and during the scan, its conformity with existing SAR limits has to be verified to ensure patient safety. We developed, implemented, and verified a new comprehensive RF patient-safety-supervision concept that combines real-time global SAR and local SAR supervision with real-time RF supervision. This new concept allows for a significantly increased permissible RF duty cycle, improves the detection of SAR limit violations and patient-unsafe conditions, and reduces the number of false-positive scan interruptions.

17:18 0176.   Safety of tattoos in MRI: an interim report on a prospective study - permission withheld
Nikolaus Weiskopf1, David Bradbury1, Sheila Burns1, and Janice Glensman1
1Wellcome Trust Centre for Neuroimaging, University College London, London, United Kingdom

Only few studies are published on the safety of tattoos in MRI. We present an interim report on a prospective study on all healthy volunteers with tattoos who were scanned at our lab. From our sample of 127 volunteers the probability of a tattoo related adverse reaction is estimated to be lower than 4.5% when additional precautions are applied. Although this is the first prospective study on this topic avoiding several potential confounds of previous studies, the particular sample and conditions studied may still limit general conclusions.

17:30 0177.   En Route to Ultrahigh Field Cardiac MR in Patients: RF Safety Assessment of Intracoronary Stents at 7.0 T Using Numerical Simulations and E-Field Measurements
Eva Oberacker1, Lukas Winter1, Frank Seifert2, Jaroslav Marek1, Gerd Weidemann2, Eugen Hofmann3, and Thoralf Niendorf1,4
1Berlin Ultrahigh Field Facility (B.U.F.F.), Max Delbrück Center for Molecular Medicine, Berlin, Berlin, Germany, 2Physikalisch Technische Bundesanstalt, Berlin, Germany, 3Biotronik AG, Bülach, Switzerland, 4Experimental and Clinical Research Center, a cooperation of the Charité Medical Faculty and the Max Delbrück Center for Molecular Medicine, Berlin, Germany

This work performs a careful safety evaluation of RF induced heating of coronary stents including electromagnetic (EM) simulations and E-field measurements. Complex electromagnetic field coupling is investigated depending on stent type, length, location, orientation, vessel diameter and RF coil used. Electromagnetic (EM) and thermal simulations were performed in phantoms and human voxel models and validated in ASTM phantom measurements. The results are transferrable to various RF coil designs and may be utilized to estimate safe RF exposure levels for SAR personalized UHF-MR exams including patients with intracoronary and other vascular stent implants.

17:42 0178.   
A Simulation Based Validation of a pTx Pulse Design Strategy Using Implant-Friendly Modes for Patients with DBS Implants
Yigitcan Eryaman1,2, Bastien Guerin2, Can Akgun3, Joaquin L. Herraiz1, Adrian Martin1,4, Angel Torrado-Carvajal1,5, Norberto Malpica1,5, Juan A. Hernandez-Tamames1,5, Emanuele Schiavi1,4, Elfar Adalsteinsson6,7, and Lawrence L. Wald2,7
1Madrid-MIT M+Vision Consortium in RLE, MIT, Cambridge, Massachusetts, United States, 2Martinos Center for Biomedical Imaging, Dept. of Radiology, MGH, Charlestown, MA, United States, 3Invenshure, MN, United States, 4Dept. of Applied Mathematics, Rey Juan Carlos University, Madrid, Spain, 5Dept. of Electronic Technology, Rey Juan Carlos University, Madrid, Spain, 6Dept. of Electrical Engineering and Computer Science, MIT, Cambridge, Massachusetts, United States, 7Harvard-MIT Health Sciences and Technology, MIT, Cambridge, MA, United States

We present a pulse design strategy that can be used to safely scan patients with implants. Our strategy is based on utilizing implant friendly modes which are defined as the modes of an array that cancel the local SAR around the implant lead tip. We performed EM simulations using a multi-tissue realistic head model with a generic deep brain stimulator implant. As a result of the pulse design, local SAR at the lead tip is reduced below SAR limits. A uniform axial flip angle distribution is obtained.

17:54 0179.   
SAR optimised local B1+ shimming for cardiac imaging at 3T – a multi-model study
Arian Beqiri1, Francesco Padormo1,2, Jeff W. Hand1, 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

Cardiac imaging at high field suffers from image quality issues due to greater B1+ inhomogeneities and is frequently limited by SAR, which constrains the speed at which scans can be run without exceeding regulatory limits. By using parallel transmission MRI, we demonstrate the ability to significantly reduce SAR whilst simultaneously improving B1+ homogeneity in order to optimise imaging over the cardiac region for two differently sized subjects. We also show the effects of selecting the wrong SAR model for each subject.

Robert A. Pooley1, Krzysztof R. Gorny2, Christopher P. Favazza2, Joel P. Felmlee2, Chen Lin3, Matt A. Bernstein2, and Robert E. Wharen4
1Radiology, Mayo Clinic, Jacksonville, Florida, United States, 2Radiology, Mayo Clinic, Rochester, MN, United States, 3Radiology and Imaging Science, IU School of Medicine, Indianapolis, IN, United States, 4Neurosurgery, Mayo Clinic, Jacksonville, Florida, United States

Temperature measurements were made in a phantom at the tip of a deep brain stimulator lead. The DBS components were arranged in various configurations and scanned at high and low SAR with body coil transmit. The temperature increase for the lead only and lead + insertion stylet was in the range of 0.5 - 3.2C at high SAR and < 0.1C at low SAR. The full DBS system resulted in heating of 14.4C at high SAR and 0.25C at low SAR. There is increasing interest in evaluating heating of leads with body coil RF transmit, which is contraindicated.

18:18 0181.   
Virtual Tissue Electrical Properties: A New Concept for Fast, Robust Local SAR Estimation Based on B1 Measurement
Xiaotong Zhang1, Pierre-Francois Van de Moortele2, Jiaen Liu1, Sebastian Schmitter2, and Bin He1,3
1Department of Biomedical Engineering, University of Minnesota, Minneapolis, MN, United States, 2Center for Magnetic Resonance Research, University of Minnesota, Minneapolis, MN, United States, 3Institute for Engineering in Medicine, 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 predict in real-time on a per-subject basis local SAR induced by RF pulsing. To reduce error propagation along the reconstruction, we eliminate the need for computing EPs by introducing the concept of ‘virtual tissue EPs’ (VEPs), tailored to provide max local SAR estimation based on measured B1 maps, with a safety margin. We evaluate the concept on electromagnetic models (EM) and in-vivo data of head imaging at 7T.