Bachschmidt Theresa J, Köhler Michael, Nistler Jürgen, Geppert Christian, Jakob Peter M, Nittka Mathias
Department of Experimental Physics 5, University of Würzburg, Würzburg, Germany.
Magnetic Resonance, Siemens AG, Erlangen, Germany.
Magn Reson Med. 2016 Jan;75(1):217-26. doi: 10.1002/mrm.25621. Epub 2015 Feb 13.
To investigate the benefit of a two-channel transmit system on shading close to total hip replacements and other elongated metal structures in parallel to the magnet bore.
An analytical model comprising a water cylinder and a metal rod is introduced to describe the B1 effects close to elongated metal structures and it is verified. The dependence of the optimal polarization, which induces minimum shading, on the position of the metal is analyzed. Furthermore, the optimal polarization for two patients is determined both on the basis of the model and experimentally and its benefit compared with circular polarization is investigated.
The cylindrical model approximates the modification of the B1 field due to the metal well, and the optimal polarization strongly depends on the position of the rod. In vivo, shading can be ameliorated by the use of the optimal polarization; for total hip replacements with shafts of titanium, this polarization can be determined on the basis of both the analytical model and the experimental data.
Parallel transmission offers the possibility of a substantial reduction of shading close to long metal structures in parallel to the magnet bore.
研究双通道发射系统对靠近全髋关节置换物及其他与磁体孔平行的细长金属结构处阴影的改善效果。
引入一个包含水缸和金属棒的分析模型来描述靠近细长金属结构处的B1效应，并对其进行验证。分析了诱导最小阴影的最佳极化对金属位置的依赖性。此外，基于该模型并通过实验确定了两名患者的最佳极化，并研究了其与圆极化相比的优势。
圆柱形模型很好地近似了由于金属导致的B1场的变化，并且最佳极化强烈依赖于金属棒的位置。在体内，使用最佳极化可改善阴影；对于钛柄全髋关节置换物，可根据分析模型和实验数据确定这种极化。
并行传输提供了大幅减少靠近与磁体孔平行的长金属结构处阴影的可能性。
