Brink Wyger M, Börnert Peter, Nehrke Kay, Webb Andrew G
C.J. Gorter Center for High Field MRI, Department of Radiology, Leiden University Medical Center, Leiden, The Netherlands.
NMR Biomed. 2014 Jun;27(6):617-20. doi: 10.1002/nbm.3112. Epub 2014 Apr 14.
The objective of this work was to explore the origin of local B1 (+) perturbations in the ventricles measured at 7 T. The B1 (+) field in the human brain was mapped using four different MRI techniques: dual refocusing echo acquisition mode (DREAM), actual flip-angle imaging (AFI), saturated double-angle method (SDAM) and Bloch-Siegert shift (BSS). Electromagnetic field simulations of B1 (+) were performed in male and female subject models to assess the dependence of the B1 (+) distribution on the dielectric properties of cerebrospinal fluid and subject anatomy. All four B1 (+) mapping techniques, based on different B1 (+) encoding mechanisms, show 'residual' structure of the ventricles, with a slightly enhanced B1 (+) field in the ventricles. Electromagnetic field simulations indicate that this effect is real and arises from the strong contrast in electrical conductivity between cerebrospinal fluid and brain tissue. The simulated results were in good agreement with those obtained in three volunteers. Measured local B1 (+) perturbations in the ventricles at 7 T can be partially explained by the high contrast in electrical conductivity between cerebrospinal fluid and white matter, in addition to effects related to the particular B1 (+) measurement technique used.
这项工作的目的是探究在7T磁场下测量到的心室局部B1(+)扰动的起源。使用四种不同的MRI技术对人脑的B1(+)场进行映射：双重聚焦回波采集模式（DREAM）、实际翻转角成像（AFI）、饱和双角法（SDAM）和布洛赫-西格特位移（BSS）。在男性和女性受试者模型中进行了B1(+)的电磁场模拟，以评估B1(+)分布对脑脊液介电特性和受试者解剖结构的依赖性。基于不同B1(+)编码机制的所有四种B1(+)映射技术均显示出心室的“残余”结构，心室内的B1(+)场略有增强。电磁场模拟表明，这种效应是真实存在的，并且源于脑脊液与脑组织之间电导率的强烈差异。模拟结果与在三名志愿者身上获得的结果高度吻合。除了与所使用的特定B1(+)测量技术相关的影响外，在7T磁场下心室中测量到的局部B1(+)扰动可以部分地由脑脊液与白质之间电导率的高差异来解释。
