MANIPULATION OF IMAGE INTENSITY DISTRIBUTION AT 70 T

这个子项目是许多研究子项目中利用 资源由NIH/NCRR资助的中心拨款提供。子项目和 调查员(PI)可能从NIH的另一个来源获得了主要资金， 并因此可以在其他清晰的条目中表示。列出的机构是 该中心不一定是调查人员的机构。 7.0T图像光强分布的操纵：介质材料的无源射频匀场和聚焦 目的：研究高介电常数填充材料对7.0T下人体头部射频场分布的影响，论证利用这种方法进行射频被动匀场和聚焦的可行性和有效性。 材料和方法：在温度为7.0T的条件下，用特定配置的水垫(介电常数为78)采集人头的梯度回波(GRE)和自旋回波(SE)图像，并与计算机模拟结果进行比较。通过计算机模拟确定了给定介质填充结构的位移电流和传导电流对B1场分布变化的贡献。 结果：在7.0T射频线圈的人体头部放置水垫可以显著改变头部的MR图像强度分布。计算机模拟表明，水垫的高介电常数导致了强大的位移电流，从而增强了附近区域的成像强度，并改变了整个大脑的强度分布。

This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Manipulation of image intensity distribution at 7.0 T: Passive RF shimming and focusing with dielectric materials PURPOSE: To investigate the effects of high dielectric material padding on RF field distribution in the human head at 7.0 T, and demonstrate the feasibility and effectiveness of RF passive shimming and focusing with such an approach. MATERIALS AND METHODS: The intensity distribution changes of gradient-recalled-echo (GRE) and spin-echo (SE) images of a human head acquired with water pads (dielectric constant = 78) placed in specified configurations around the head at 7.0 T were evaluated and compared with computer simulation results using the finite difference time domain (FDTD) method. The contributions to the B1 field distribution change from the displacement current and conductive current of a given configuration of dielectric padding were determined with computer simulations. RESULTS: MR image intensity distribution in the human head with an RF coil at 7.0 T can be changed drastically by placing water pads around the head. Computer simulations reveal that the high permittivity of water pads results in a strong displacement current that enhances image intensity in the nearby region and alters the intensity distribution of the entire brain.