MRI Technology for Enhanced Radio Frequency Safety

Stanford University, Stanford CA

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Abstract

DESCRIPTION (provided by applicant): The overall goal of this work is to create an MRI imaging environment that eliminates the possibility of RF burns for recipients of cardiac pacemaker, deep brain stimulator, and other neuro-stimulator devices. Today, about 3 million Americans have implanted pacemakers that typically contraindicate any form of head, chest, or muskulo-skeletal MRI scan. Recent clinical safety studies for imaging device recipients at 1.5T have been performed without incident and no related fatalities for pacemakers have occurred since the 1980s. Guidelines for deep brain stimulator recipients typically require head transmit coils and only at 1.5T but at least two MR induced brain injuries have occurred at 1.0T. The general failure to identify adverse outcomes does not prove safety because these results cannot be extrapolated to other field strengths; guidelines are tied to scanner power which is reported inconsistently, and MRI systems lack robust methods of predicting and avoiding potential heating conditions based on physically existing preconditions. Improved engineering of the MR scanner itself can solve this problem. This will require an integration of electromagnetic safety sensors that can independently detect or search for dangerous resonances, MRI RF field mapping methods that can detect lead wire currents responsible for heating but at sensitivities well below physical heating thresholds, and distributed transmit array systems that deposit RF power only where needed. If the physical conditions for heating can be detected and imaged, regardless of field strength, patient orientation, or device, an RF excitation system can be designed to prevent heating. The aims of this research are to: 1) Develop an RF safety prescreen system to detect dangerous interactions before the MRI scan. Integrated external sensor systems will be developed for 1.5T, and extended to 3T. These systems will detect potential resonant device interactions that may produce RF heating and can be used before the patient even enters the MRI scan room. 2) Develop an MRI safety pre-scan to detect and quantify dangerous interactions with a low power MRI scan. MRI pulse sequences will detect and quantify induced RF currents on conductive structures, and use these measurements to grade risk, and predict potential heating for other sequences. 3) Develop safer MRI systems for the future using advanced RF transmission methods. Transmit array excitation systems and optimized pulse sequences will minimize electromagnetic coupling and RF heating near implanted devices. This will be tested in an in vivo animal model at 3T to show that RF currents on an implanted lead can be nulled while providing a sufficiently uniform RF field for imaging. .Ultimately, this work will lead to a clinically testable system. Achieving these goals will substantially increase access to MRI for a broad class of patients with cardiac or neuro-stimulator implants who are currently denied access out of fear of RF heating danger. PUBLIC HEALTH RELEVANCE: Technology to enhance RF safety in MRI scanners- is important to public health because it will enable the 3 million Americans with cardiac pacemakers or deep brain stimulator implants to safely undergo MRI exams without fear of unintended local RF burns. Underutilization of MRI scanners with these patients can be avoided, and the risk of adverse events or unsafe settings can be substantially eliminated.