|Targeting RF Safety in Implants & Interventions|
|Permanent Non-Invasive Device Safety Monitoring for
Sascha Krueger1, Daniel Wirtz1, Dennis Glaesel1, Ingmar Graesslin1
1Philips Research Europe, Hamburg, Germany
The use of devices containing electric leads or conductive structures is associated with an inherent safety risk for the patient and the physician. The presence of a device inside a patient (e.g.pacemaker) or the necessity to use other devices for diagnosis and treatment (e.g.catheters/guidewires) is, therefore, currently often a contraindication for an MR examination. Virtually any device containing conductive parts may become unsafe and may malfunction under certain conditions. Therefore, a generic detection mechanism of unsafe situations during clinical MRI scans is proposed. Deviations from the RF demand are detected in real-time by monitoring the RF transmission during the MR imaging experiment.
An Optically-Coupled System for Quantitative
Monitoring of MRI-Induced RF Currents Into Long Conductors
Marta Gaia Zanchi1, Ross Venook2, John Mark Pauly1, Greig Scott1
1Stanford University, Stanford, California , USA; 2Advanced Bionics, Sylmar, California , USA
MRI-induced RF currents in interventional devices pose safety risks that cannot be reliably predicted. We have developed and validated an optically-coupled system capable of quantitatively monitoring in real-time the RF currents induced in long conductors. We have tested it in a birdcage RF safety platform with cable-traps and Q-spoiling loads that reduce the RF currents.
Monitoring Induced Currents on Long
Conductive Structures During MRI
Ross D. Venook1, 2, William R. Overall1, Kim Shultz1, Steven Conolly3, John M. Pauly1, Greig C. Scott1
1Stanford University, Stanford, California , USA; 2Boston Scientific, Burlingame, California , USA; 3U.C. Berkeley, Berkeley, California , USA
This abstract presents an image-based method for measuring induced axial RF currents on a long conductive structure during an MRI experiment. Extensions of this method represent a way to verify and monitor safety of certain devices and guidewires during an MRI procedure.
Measuring RF-Induced Currents Inside Implants: Impact
of Device Configuration on MRI Safety of Cardiac Pacemaker Leads
Peter Nordbeck1, 2, Ingo Weiss2, Philipp Ehses1, Marcus Warmuth1, Florian Fidler3, Peter M. Jakob1, 3, Mark E. Ladd4, Harald H. Quick4, Wolfgang R. Bauer1
1University of Würzburg, Würzburg, Germany; 2Biotronik GmbH & Co. KG, Berlin, Germany; 3Research Center Magnetic Resonance Bavaria, Würzburg, Germany; 4University of Duisburg-Essen, Essen, Germany
RF-related heating of elongated conductive implants such as cardiac pacemaker leads is a serious concern in magnetic resonance imaging (MRI). The implant configuration has been shown to be an important factor in the amount of induced heating, but this issue is still poorly understood, possibly because temperature measurements are very time consuming and particularly vulnerable to positioning errors of the probes. In this study, the electric currents induced inside the implant were measured and correlated to implant heating. This approach allows for fast, systematic and reproducible investigation of the impact of a cardiac implant’s configuration on MRI-related heating effects.
The Effect of Lead Length on Lead Tip
Heating in Orphan Leads Verses Leads Connected to Pacemakers at 1.5T
Deborah Anne Langman1, Mayil Krishnam1, Noel G. Boyle1, John Paul Finn1
1UCLA, Los Angeles, California , USA
Current safety guidelines label implanted pacemakers as a contraindication for MRI scanning due in part to risks of tissue damage from pacemaker lead tip heating. The goal of this research was to explore the lead tip heating in orphan pacemaker leads compared to leads connected to pacemakers at 1.5T. For clinical lead lengths on the order of 40-57cm the lead tip heating will be worse for capped orphan leads. For shorter lead lengths the resonance effect diminishes lead tip heating when the lead is capped, however heating increases when the pacemaker is connected. It is therefore important to consider the length of the lead implanted when comparing safety of orphan leads verses leads connected to pacemakers.
Clinical Trial to Evaluate Pacemaker Safety and
Efficacy in MRI Environment: Device and Study Design
Emanual Kanal1, Torsten Sommer2, David Bello3, Roger Luenchinger4, Richard Sutton5, Bruce Wilkoff6
1UPMC Presbyterian, Pittsburgh, Pennsylvania, USA; 2University of Bonn, Bonn, Germany; 3Mid-Florida Cardiology Specialists, Orlando, Florida, USA; 4University Hospital, Zurich, Switzerland; 5St. Mary's Hospital, London, UK; 6Cleveland Clinical Foundation, Cleveland, Ohio, USA
Up to 75% of pacemaker patients need an MRI during the life-time of the pacemaker, therefore MRI-pacemaker compatibility is a significant need. A pacemaker system has been designed and pre-clinically tested for MRI compatibility in a controlled environment. The new pacemaker system is designed to minimize lead tip heating and induced energy on leads. A pacemaker feature also eliminates the impact of MRI-generated electrical noise. A randomized clinical trial has started in 2007 to enroll 470 patients to evaluate safety and efficacy of the pacemaker system in an MRI environment. Patients are randomized to receive MRI or no MRI scan.
|A Combined Approach to Assessing Safety
of Depth Electrodes and Microwires at 3 Tesla
Debra S. Strick1, Mark S. Cohen, Jack W. Judy, Frank G. Shellock
1University of California Los Angeles, Westwood, USA
Implants inadvertently acting as antenna can cause dangerous levels of MR-related heating. The resultant heating can greatly vary due to the non-linear behavior of structures near resonance. We combine heating experiments with characterization of resonant frequency profiles to minimize the uncertainty of safety characterization for a depth electrode and microwire array at 3-Tesla.
|Experimental and Numerical Determination of SAR and
Temperature Distribution of a Human Endorectal Coil for MR Imaging of
the Prostate at 7T
Andreas K. Bitz1, Dennis W.J. Klomp2, Mark E. Ladd1
1Erwin L. Hahn Institute for Magnetic Resonance Imaging, Essen, Germany; 2Radboud University Nijmegen Medical Centre, Nijmegen, Netherlands
Compliance testing of a transmit and receive endorectal loop coil with respect to the SAR and temperature limits given in the IEC guidelines is performed by numerical calculation of the RF field and SAR distribution as well as experimental temperature measurements in a phantom and in the human prostate in vivo. The results show that for a maximum permissible time-averaged power of 0.76 W, the proposed endorectal coil complies with the SAR and temperature limits given in the IEC guidelines.
Whole Shaft Visibility for Polymer-Based Active IMRI
Catheters Using Hybrid Braided Tubes
Ozgur Kocaturk1, Ann Kim1, Michael A. Guttman1, Anthony Faranesh1, Andrew J. Derbyshire1, Kanishka Ratnayaka1, Robert J. Lederman1
1National Institutes of Health, Bethesda, Maryland, USA
For MR-guided interventional devices, visualization of the tip and shaft is essential for safe tracking during minimally invasive procedures. Hybrid coaxial braided tubes were implemented into the polymer-based catheter to construct a monopole antenna. Copper wires in the braiding resulted in acceptable RF transmission over the designed monopole stub, while nitinol wires lent mechanical stability to the catheter. Two distal loop coils were also implemented into the catheter body to visualize the tip and its orientation. Good visibility of the tip and whole shaft was observed in vivo and in vitro real time scanning. Torquability and pushability remained unaffected.
Preclinical Evaluation of a Novel Fiber Compound MR
Nils A. Kraemer1, Sascha Krueger2, Sebastian Schmitz3, Marita Linssen4, Heinz Schade5, Steffen Weiss2, Rolf W. Guenther1, Arno Buecker6, Gabriele A. Krombach1
1RWTH Aachen, Aachen, Germany; 2Philipps Research Europe, Hamburg, Germany; 3Fraunhofer Institute for Production Technology, Aachen, Germany; 4Hemoteq GmbH, Wuerselen, Germany; 5Andramed GmbH, Reutlingen, Germany; 6University Clinic Saarland, Homburg, Germany
An MR-conditional guide wire (GW) was evaluated in an animal model. The GW consists of a fiber glass compound with an Nitinol tip. Iron powder within the compound and iron markings improve MR visibility. Using real time MRI-guidance with balanced-SSFP sequences, various MR-interventions were performed (stent placement, embolization or direct MR angiography). Time to reach the target, induced artifacts and handling were assessed. The GW was clearly depictable on real time MRI. The GW allowed reaching all target vessels, and all interventions were completed successfully.