ESMRMB 2016, 33rd Annual Scientific Meeting, Vienna, AT, September 29–October 1: Abstracts, Thursday
ESMRMB 2016, 33rd Annual Scientific Meeting, Vienna, AT, September 29–October 1: Abstracts, Thursday
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DOI：
10.1007/s10334-016-0568-x
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发表时间：
2016-09
期刊：
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通讯作者：
K. Sofya;Nazarova Maria;Лимонова Алёна Сергеевна;Пирадов Михаил Александрович;Коновалов Родион Николаевич;Добрынина Лариса Анатольевна
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作者：
K. Sofya;Nazarova Maria;Лимонова Алёна Сергеевна;Пирадов Михаил Александрович;Коновалов Родион Николаевич;Добрынина Лариса Анатольевна
目的/简介生物组织和空气腔中不同磁化率产生的场不均匀性随外加静磁场线性增加。最近的方法证明了在阵列配置中使用不规则形状的线圈元件[1,2]而不是在接近的B0矩阵垫片中使用环路元件[3,4]的优势。我们引入了描述每个单个线圈的几何形状和位置的独立参数，然后共同优化。在模拟中，一组线圈被放置在一个圆柱体（约360 mm）上，该圆柱体足够大，可以容纳额外的射频发射和接收阵列。优化程序是基于在志愿者大脑中获得的场或频率图。一种方法是设计单独的设置，每个设置包含6个在单个切片上优化的线圈。例如，在2个不同的切片上调整了2个设置之后，我们可以将它们全部容纳在一个总共有12个通道的圆柱体上。第二种方法是采用16个通道并配置它们，以便同时优化不同切片的精度。不同设置的比较是基于得到的磁场分布的标准偏差（以赫兹为单位）。两片优化只是为了概念验证，在未来的优化将在几个片或指定的卷上执行。结果图1显示了第二次shshim后的切片，以及为特定切片使用6通道优化设置后的切片。图2显示了在2片上同时优化设置后产生的shim场。单片优化后的最终标准差与同时优化后的最终标准差非常相似。相比之下，在片1上仅包含环路元素的32通道设置调光后的标准偏差为13.4，片2为11.1 Hz。因此，所提出的不规则线圈在不对称位置上得到的标准差更好。讨论/结论数值模拟表明，与传统的仅包含圆形元件的阵列相比，使用不规则几何形状的线圈具有显著的优势。未来的工作将包括在给定体积上进行的优化和所提议结构的实际实现。
Purpose/IntroductionThe field inhomogeneities produced by different susceptibilities in biological tissue and air cavities increase linearly with the applied static magnetic field. The most recent approach demonstrated advantage of using irregularly shaped coil elements in an array configuration [1, 2] instead of loop elements [3, 4] in close fitting B0 matrix shim. We introduce independent parameters describing a geometry and position of every single coil which are then optimized jointly.Subjects and MethodsFor the simulations, a set of coils were placed on a cylinder (ø 360 mm), which is large enough to accommodate inside additional RF transmit and receive arrays. The optimization procedure was based on a field or frequency map that was acquired within the brain of a volunteer. One approach was to design individual setups, each one containing 6 coils optimized on a single slice. After having, for example, 2 setups tuned on 2 different slices we could accommodate them all on a cylinder having in total 12 channels. The second approach was to take 16 channels and configure them so as to optimize an accuracy over different slices simultaneously. The comparison of different setups was based on the standard deviation (in Hz) of the resulting magnetic field distributions. Two-slice optimization is just for proof of concept, in the future optimization will be performed on several slices or on the specified volume.ResultsFigure 1 shows the slices after 2nd SH shim and after shimming with 6 channel optimized setups for a particular slice. Figure 2 shows the resulting shim field after simultaneous optimization of the setup on 2 slices. The final standard deviation after optimization on a single slice and after simultaneous optimization was very similar. For comparison, standard deviation after shimming with a 32 channel setup containing only loop elements on slice 1 was 13.4 and on slice 2 was 11.1 Hz. Thus, the resulting standard deviation was better with the proposed irregular coils on asymmetric positions.Discussion/ConclusionIt is shown by numerical simulations that there is a significant advantage of using coils with irregular geometries over traditional arrays containing only circular elements. Future work will include optimization performed on a given volume and practical realization of the proposed structures.