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。此外，保证射频安全是在MRI下进行图像引导介入的必要要求。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。我们相信，射频安全设备的解决方案在于改进磁共振扫描仪本身的工程。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MR测温或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。如果我们可以检测和成像是否存在加热的物理条件，无论场强、患者方向或设备如何，我们都可以创建阻止加热的射频激励系统。具体地说，我们的目标是：1)开发患者外部的电磁安全设备，预先筛选危险的谐振条件，实时检测导线电流，或抑制导线共振。2)开发MRI脉冲序列，以检测和量化低于MR温度计检测所需灵敏度的RF电流的存在。3)开发具有优化脉冲序列的发射阵列激励系统，在保持图像质量的同时防止植入器件附近的电磁耦合和射频加热。我们的方法最终涉及使用发射阵列元件定位功率沉积区域，但即使使用标准发射线圈、独立的RF传感器和/或专门的MRI场映射方法，也将为确定是否存在RF危险提供可量化的客观基础。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. Moreover, guaranteed RF safety is a necessary requirement for image guided interventions to be performed under MRI. 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. We believe the solutions for RF safe devices lie in improved engineering of the MR scanner itself. 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 the MR thermometry or physical heating thresholds, and distributed transmit array systems that deposit RF power only where needed. If we can detect and image if the physical conditions exist for heating, regardless of field strength, patient orientation, or device, we can create RF excitation systems that prevent heating. Specifically, our aims are to: 1) Develop electromagnetic safety devices external to the patient that prescreen for dangerous resonant conditions, detect wire currents in real time, or inhibit wire resonances. 2) Develop MRI pulse sequences that detect and quantify the presence of RF currents at levels below the sensitivity needed for detection by MR thermometry. 3) Develop transmit array excitation systems with optimized pulse sequences that maintain image quality but prevent electromagnetic coupling and RF heating near implanted devices. Our approach ultimately involves localizing the region of power deposition with transmit array elements, but even with standard transmit coils, independent RF sensors and/or specialized MRI field mapping methods will give a quantifiable and objective basis for determining if an RF hazard can exist. Achieving these goals will substantially increase access to MRI for a broad class of patients with cardiac or neurostimulator implants who are currently denied access out of fear of RF heating danger.