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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.

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.

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.

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.

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.

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.

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.

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.

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.

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.