Passive antennas for improved image quality in transcranial MR-guided focused ultrasound

项目总结/摘要 经颅磁共振引导聚焦超声（tcMRgFUS）神经外科是一种非侵入性治疗， 特发性震颤、神经性疼痛和许多新兴应用。tcMRgFUS系统具有水浴 它将声能耦合到头部，并在声波治疗之间循环冷却头皮。水 然而，浴还充当具有比自由空间短得多的RF波长的高介电常数电介质。在 同时，换能器碗是导电的，所以当电磁波产生时， 用于成像的MRI扫描仪进入浴槽，它们穿过换能器碗中的浴槽并反射 碗的内表面在头部上方。反射波然后与入射波抵消， 导致图像中具有非常低的MR信号的暗带，并且整个大脑通常为低信号。的 低信号限制了可用于指导和评估tcMRgFUS治疗的扫描类型，尤其是自旋 回声扫描，如扩散，可以实现早期病变和基于纤维束成像的评估。到 为了解决这个问题，我们提出了一种新型的无源反射天线，将坐在水浴 在头部上方，并且将产生其自己的波反射，该波反射可以被控制以便建设性地增加 输入波，从而将MR信号恢复到与成像外部的成像相称的水平。 传感器电线将不需要电连接，并且可以做得非常细，以避免干扰电连接。 超声波束我们还建议开发一种互补的无源环形线圈环， 在传感器底部的外部，进一步增加大脑中的磁场。我们将使用电磁 MRI扫描仪中的tcMRgFUS系统的仿真，以优化天线和环形线圈，设计 用于它们的机械保持器，其不干扰超声波束并且不需要修改 换能器，然后在临床tcMRgFUS系统中对健康志愿者的MR成像进行评估。

Project Summary/Abstract Transcranial MR-guided focused ultrasound (tcMRgFUS) neurosurgery is a non-invasive treatment for essential tremor, neuropathic pain, and many emerging applications. tcMRgFUS systems have a water bath that couples acoustic energy into the head and is circulated to cool the scalp between sonications. The water bath, however, also acts as a high permittivity dielectric with a much shorter RF wavelength than free space. At the same time, the transducer bowl is electrically conductive, so when the electromagnetic waves generated by the MRI scanner for imaging enter the bath, they travel through the bath in the transducer bowl and reflect off the bowl’s inner surface above the head. The reflected waves then cancel with the incoming waves which causes a dark band with very low MR signal in the images, and generally low signal throughout the brain. The low signal limits the types of scans that can be used to guide and assess tcMRgFUS treatment, especially spin echo scans such as diffusion which could enable earlier lesion and tractography-based assessment. To address this problem, we propose to develop a novel passive reflecting antenna that will sit in the water bath above the head, and will create its own wave reflection that can be controlled so as to add constructively with the incoming wave, thereby restoring the MR signal to levels commensurate with imaging outside the transducer. The wires will require no electrical connections and can be made very thin to avoid disturbing the ultrasound beam. We also propose to develop a complementary ring of passive loop coils that would sit outside the bottom of the transducer and further increase the fields in the brain. We will use electromagnetic simulations of a tcMRgFUS system in an MRI scanner to optimize the antennas and loop coils, design mechanical holders for them that do not disturb the ultrasound beams and do not require modifying the transducer, and then evaluate them in MR imaging of healthy volunteers in a clinical tcMRgFUS system.