PARALLEL IMAGING PERFORMANCE AS A FUNCTION OF FIELD STRENGTH AN EXPERIMENTAL IN

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。 在这项工作中，实验研究了并行磁共振成像性能与主磁场强度的关系。利用电动力学标度的一般框架，研究了在7T的单个物理场强下，相关射频场的B0依赖行为。在所选择的实现中，这是通过调整均匀球形体模的介电常数和电导率来实现的。用不同比例的正庚烷、乙醇、纯净水、N-甲基甲酰胺和氯化钠混合，模拟了1.5~11.5T范围内的场强。基于一个八线圈接收器阵列的灵敏度图，用反映并行成像重建中噪声增强的几何因子g来评估并行成像的场相关性能。在低场强时，信噪比损失几乎与B0无关，当一维简化因子在3~4之间时，信噪比损失较低。在较高场强时，有利和禁止并行成像条件之间的转换向较高可行简化因子转移。这些发现与之前的理论预测很好地吻合。根据这一协议，得出结论，高B0的并行MRI特别受益于设置所涉及的射频场的远场行为。

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. In this work, the dependence of parallel MRI performance on main magnetic field strength is experimentally investigated. Using the general framework of electrodynamic scaling, the B0-dependent behavior of the relevant radiofrequency fields at a single physical field strength of 7 T is studied. In the chosen implementation this is accomplished by adjusting the permittivity and conductivity of a homogeneous spherical phantom. With different mixing ratios of decane, ethanol, purified water, N-methylformamide, and sodium chloride, field strengths in the range of 1.5 to 11.5 T are mimicked. Based on sensitivity maps of an eight-coil receiver array, the field-dependent performance of parallel imaging is assessed in terms of the geometry factor g, which reflects noise enhancement in parallel imaging reconstruction. At low field strengths the SNR penalty was nearly independent of B0 and favorably low for 1D reduction factors up to between 3 and 4. At higher field strengths the transition between favorable and prohibitive parallel imaging conditions was found to shift toward higher feasible reduction factors. These findings are in good agreement with previous theoretical predictions. From this agreement it is concluded that parallel MRI at high B0 benefits specifically from onsetting far-field behavior of the involved radiofrequency fields.