Measurement and correction of transmitter and receiver induced nonuniformities in vivo
Measurement and correction of transmitter and receiver induced nonuniformities in vivo
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DOI：
10.1002/mrm.20354
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发表时间：
2005-02
影响因子：
3.3
通讯作者：
Jinghua Wang;M. Qiu;Qing Yang;Michael B. Smith;R. Constable
中科院分区：
文献类型：
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作者：
Jinghua Wang;M. Qiu;Qing Yang;Michael B. Smith;R. Constable
高场 MR 成像中的信号强度不均匀性限制了 MRI 提供定量信息的能力，并对诊断扫描质量产生负面影响。本文描述了一种基于发射场 B1+ 和接收灵敏度图的体内测量来校正这些影响的简单方法。这些图可以通过梯度回波 (GE) 或自旋回波 (SE) 成像序列在体内获得，但 SE 方法在纠正一系列翻转角度上的图像方面表现出优于 GE 方法的优势。在均匀体模中，这种方法将信号 SD 与其平均值的比率从校正前的约 30% 降低到校正后 SE 方法的约 6% 和 GE 方法的 9%。使用 3.0 T 的传统自旋回波序列获得的人脑图像在体内证明了 SE 方法在校正强度不均匀性方面的应用。此外，还表明可以使用分段回波平面成像序列执行体内 B1+ 和接收灵敏度映射，提供小于 2 分钟的采集时间。尽管这里提出的校正是通过同时发射和接收体线圈进行演示的，但它可以扩展到单独发射和接收线圈的情况，包括表面和相控阵线圈。 Magn Reson Med 53:408–417, 2005。© 2005 Wiley-Liss, Inc.
Signal intensity nonuniformities in high field MR imaging limit the ability of MRI to provide quantitative information and can negatively impact diagnostic scan quality. In this paper, a simple method is described for correcting these effects based on in vivo measurement of the transmission field B1+ and reception sensitivity maps. These maps can be obtained in vivo with either gradient echo (GE) or spin echo (SE) imaging sequences, but the SE approach exhibits an advantage over the GE approach for correcting images over a range of flip angles. In a uniform phantom, this approach reduced the ratio of the signal SD to its mean from around 30% before correction to approximately 6% for the SE approach and 9% for the GE approach after correction. The application of the SE approach for correcting intensity nonuniformities is demonstrated in vivo with human brain images obtained using a conventional spin echo sequence at 3.0 T. Furthermore, it is also shown that this in vivo B1+ and reception sensitivity mapping can be performed using segmented echo planar imaging sequences providing acquisition times of less than 2 min. Although the correction presented here is demonstrated with a simultaneous transmit and receive volume coil, it can be extended to the case of separate transmission and reception coils, including surface and phase array coils. Magn Reson Med 53:408–417, 2005. © 2005 Wiley‐Liss, Inc.