MRI Technology for Enhanced Radio Frequency Safety

描述(申请人提供)：这项工作的总体目标是创造一个MRI成像环境，消除心脏起搏器、脑深部刺激器和其他神经刺激器设备的接受者发生射频烧伤的可能性。今天，大约有300万美国人植入了起搏器，这些起搏器通常禁止进行任何形式的头部、胸部或麝香骨骼MRI扫描。最近对1.5T成像设备接受者进行的临床安全性研究没有发生任何事件，自20世纪80年代以来没有发生过与起搏器相关的死亡事件。深部脑刺激器接受者指南通常要求头部传输线圈，仅在1.5T时，但至少有两例MR导致的脑损伤在1.0T时发生。一般未能识别不良结果并不能证明是安全的，因为这些结果不能外推到其他磁场强度；指南与扫描仪功率捆绑在一起，这是不一致的，磁共振成像系统缺乏基于物理上存在的前提条件预测和避免潜在加热条件的可靠方法。改进的磁共振扫描仪本身的设计可以解决这个问题。这将需要集成可以独立检测或搜索危险共振的电磁安全传感器，可以检测导致加热但灵敏度远低于物理加热阈值的引线电流的核磁共振射频场映射方法，以及仅在需要时存储射频功率的分布式发射阵列系统。如果无论场强、患者方向或设备如何，都可以检测和成像加热的物理条件，就可以设计射频激励系统来防止加热。本研究的目的是：1)开发一种射频安全预筛选系统，以便在MRI扫描之前检测危险的相互作用。集成的外部传感器系统将为1.5T开发，并扩展到3T。这些系统将检测可能产生射频加热的潜在共振设备相互作用，甚至可以在患者进入MRI扫描室之前使用。2)开发MRI安全预扫描，以检测和量化与低功率MRI扫描的危险交互作用。磁共振脉冲序列将检测和量化导电结构上的感应射频电流，并使用这些测量来对风险进行评级，并预测其他序列的潜在加热。3)使用先进的射频传输方法，开发更安全的磁共振成像系统。发射阵列激励系统和优化的脉冲序列将最大限度地减少植入设备附近的电磁耦合和射频加热。这将在3T的活体动物模型中进行测试，以表明植入导线上的射频电流可以被消除，同时为成像提供足够均匀的射频磁场。最终，这项工作将导致一个临床可测试的系统。实现这些目标将大大增加接受心脏或神经刺激器植入物的广泛类别的患者获得核磁共振的机会，这些患者目前因担心射频加热危险而被拒绝。

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.