Simultaneous B(0)- and B(1)+-map acquisition for fast localized shim, frequency, and RF power determination in the heart at 3 T.
Simultaneous B(0)- and B(1)+-map acquisition for fast localized shim, frequency, and RF power determination in the heart at 3 T.
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DOI：
10.1002/mrm.22234
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发表时间：
2010-02
影响因子：
3.3
通讯作者：
Stuber, Matthias
中科院分区：
文献类型：
--
作者：
Schaer, Michael;Vonken, Evert-Jan;Stuber, Matthias
高场（≥ 3 T）心脏MRI受到静磁场B 0和发射射频（RF）场B1+不均匀性的挑战。不均匀的B场不仅需要改进的匀场方法，而且它们还阻碍了零阶项的正确确定，即局部谐振频率f0和RF功率以生成预期的局部B1+场。在这项工作中，双回波时间B 0地图和双翻转角B1+地图采集方法相结合，以获得多切片B 0和B1+地图，同时覆盖整个心脏在一个单一的18心跳的屏气。先前提出的激励脉冲形状相关的切片轮廓校正进行测试和应用，以减少系统误差的多切片B1+地图。包括频率f0和RF功率的零阶项的局部高阶匀场校正值可以基于所获取的B 0-和B1+-图来确定。该方法已在7名健康成人受试者中在3 T下进行了测试，与更常用的制备方法相比，将B 0场均匀性（标准差）从60 Hz提高到35 Hz，并将平均B1+场从所需B1+场的77%提高到100%。
High field (≥3T) cardiac MRI is challenged by inhomogeneities of both the static magnetic field B0 and the transmit radiofrequency (RF) field B1+. The inhomogeneous B fields do not only demand for improved shimming methods, but they furthermore impede the correct determination of the zero order terms, i.e. the local resonance frequency f0 and the RF power to generate the intended local B1+ field. In this work dual echo time B0-map and dual flip angle B1+-map acquisition methods are combined to acquire multi-slice B0- and B1+-maps simultaneously covering the entire heart in a single breath-hold of 18 heart beats. A previously proposed excitation pulse shape dependent slice profile correction is tested and applied to reduce systematic errors of the multi-slice B1+-map. Localized higher order shim correction values including the zero order terms for frequency f0 and RF power can be determined based on the acquired B0- and B1+-maps. This method has been tested in 7 healthy adult human subjects at 3T and improved the B0 field homogeneity (standard deviation) from 60Hz to 35Hz and the average B1+ field from 77% to 100% of the desired B1+ field when compared to more commonly used preparation methods.
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