MRI Technology For Enhanced Radio Frequency Safety

描述（由申请人提供）：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、深部脑刺激器和其他神经刺激器装置接受者射频烧伤的可能性。此外，保证射频安全是在MRI下进行图像引导干预的必要要求。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、胸部或肌肉骨骼MRI扫描。自20世纪80年代以来，最近对1.5T的成像装置接受者进行的临床安全性研究没有发生事故，也没有发生与起搏器相关的死亡事件。深部脑刺激器接受者的指南通常要求头部传输线圈，并且仅在1.5T时使用，但至少有两例在1.0T时发生了MR引起的脑损伤。一般不能确定不良后果并不能证明安全性，因为这些结果不能外推到其他领域的优势；指南与扫描仪功率相关联，报告不一致，MRI系统缺乏基于物理存在的先决条件预测和避免潜在加热条件的强大方法。我们相信射频安全设备的解决方案在于改进MR扫描仪本身的工程。这将需要集成能够独立检测或搜索危险共振的电磁安全传感器，可以检测负责加热的引线电流的MRI RF场测绘方法，但灵敏度远低于MR测温或物理加热阈值，以及仅在需要时存储RF功率的分布式发射阵列系统。如果我们能够检测和成像是否存在加热的物理条件，无论场强，患者取向或设备如何，我们都可以创建防止加热的射频激励系统。具体来说，我们的目标是：1)开发患者外部的电磁安全装置，预先筛选危险的谐振条件，实时检测导线电流，或抑制导线谐振。2)开发MRI脉冲序列，检测和量化射频电流的存在，其灵敏度低于MR测温所需的检测灵敏度。3)开发具有优化脉冲序列的发射阵列激励系统，既能保持图像质量，又能防止植入设备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，但即使使用标准的发射线圈，独立的RF传感器和/或专门的MRI场测绘方法也将为确定是否存在RF危害提供可量化和客观的基础。实现这些目标将大大增加心脏或神经刺激器植入的广大患者使用MRI的机会，这些患者目前因担心射频加热危险而被拒绝使用。

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.