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建一个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器械接受者射频灼伤的可能性。此外，保证射频安全性是在MRI下进行图像引导介入的必要要求。今天，大约有300万美国人植入了心脏起搏器，通常禁忌任何形式的头部，胸部或肌肉骨骼MRI扫描。最近在1.5T下对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发射线圈，并且仅在1.5T下，但在1.0T下至少发生了两起MR诱导的脑损伤。由于这些结果无法外推至其他场强，因此无法识别不良结局的一般失败并不能证明安全性;指南与报告不一致的扫描仪功率有关，并且MRI系统缺乏基于物理存在的前提条件预测和避免潜在加热条件的可靠方法。我们认为射频安全设备的解决方案在于改进MR扫描仪本身的工程设计。这将需要集成可独立检测或搜索危险共振的电磁安全传感器、可检测导致发热但灵敏度远低于MR测温或物理发热阈值的导线电流的MRI RF场标测方法，以及仅在需要时存放存款RF功率的分布式发射阵列系统。如果我们可以检测并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，我们都可以创建防止加热的RF激励系统。具体来说，我们的目标是：1）开发患者体外的电磁安全设备，预先筛选危险的谐振条件，检测线电流在真实的时间，或抑制线谐振。2)开发MRI脉冲序列，以检测和量化RF电流的存在，其水平低于MR测温检测所需的灵敏度。3)开发具有优化脉冲序列的发射阵列激励系统，以保持图像质量，但防止植入器械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RF传感器和/或专用MRI场标测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目前因担心射频加热危险而被拒绝使用的心脏或神经刺激器植入物患者的MRI访问。

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.