Comparison of optimized intensity correction methods for 23Na MRI of the human brain using a 32-channel phased array coil a 7 Tesla
Comparison of optimized intensity correction methods for 23Na MRI of the human brain using a 32-channel phased array coil a 7 Tesla
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DOI：
10.1016/j.zemedi.2019.10.004
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发表时间：
2020-05-01
影响因子：
2
通讯作者：
Nagel, Armin M.
中科院分区：
文献类型：
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作者：
Lachner, Sebastian;Ruck, Laurent;Nagel, Armin M.
目的：校正钠磁共振成像 (Na-23 MRI) 中相控阵头部线圈的非均匀接收轮廓。方法：使用配备 32 通道仅接收阵列的双调谐正交 H-1/Na-23 发射/接收鸟笼线圈，在 7T MR 系统上对人脑 (n = 8) 进行 Na-23 MRI。为了校正不均匀的接收轮廓，应用了四种不同的方法：（1）对未校正的相控阵图像和额外采集的鸟笼图像作为参考图像进行低通滤波并相互分割（2）第二种方法用支撑区域代替参考图像。 (3) 通过对单独计算的接收轮廓进行平均，获得并应用通用灵敏度图。 (4) 接收轮廓由预扫描的大型均匀体模确定。在模拟研究中使用归一化均方根误差 (NRMSE) 优化了灵敏度图的计算。所有方法均在体模测量中进行评估，并最终应用于体内 Na-23 MRI 数据集。体内测量进行了部分体积校正，并且为了进一步评估，计算了外部和内部脑脊液室之间的信号比（CSFout：CSFin）。结果：体模测量显示了应用给定方法的强度分布的校正。与未校正的相控阵图像（NRMSE = 0.46，CSFout：CSFin = 1.71）相比，模拟和测量的强度校正人脑数据集的定量评估表明利用鸟笼图像（NRMSE = 0.39，CSFout：CSFin = 1.00）的最佳性能。然而，采用支持区域（NRMSE = 0.40，CSFout：CSFin = 1.17）、通用灵敏度图（NRMSE = 0.41，CSFout：CSFin = 1.05）或预扫描灵敏度图（NRMSE = 0.42，CSFout：CSFin = 1.07）仅显示稍差的结果。结论：获取鸟笼图像作为参考图像来校正接收配置文件显示出最佳性能。然而，当旨在减少采集时间或在没有现有鸟笼线圈的情况下进行测量时，使用支撑区域作为参考图像、通用或预扫描灵敏度图的方法为接收轮廓的校正提供了良好的替代方案。
Purpose: To correct for the non-homogeneous receive profile of a phased array head coil in sodium magnetic resonance imaging (Na-23 MRI).Methods: Na-23 MRI of the human brain (n = 8) was conducted on a 7T MR system using a dual-tuned quadrature H-1/Na-23 transmit/receive birdcage coil, equipped with a 32-channel receive-only array. To correct the inhomogeneous receive profile four different methods were applied: (1) the uncorrected phased array image and an additionally acquired birdcage image as reference image were low-pass filtered and divided by each other (2) The second method substituted the reference image by a support region. (3) By averaging the individually calculated receive profiles, a universal sensitivity map was obtained and applied. (4) The receive profile was determined by a pre-scanned large uniform phantom. The calculation of the sensitivity maps was optimized in a simulation study using the normalized root-mean-square error (NRMSE). All methods were evaluated in phantom measurements and finally applied to in vivo Na-23 MRI data sets. The in vivo measurements were partial volume corrected and for further evaluation the signal ratio between the outer and inner cerebrospinal fluid compartments (CSFout:CSFin) was calculated.Results: Phantom measurements show the correction of the intensity profile applying the given methods. Compared to the uncorrected phased array image (NRMSE = 0.46, CSFout:CSFin = 1.71), the quantitative evaluation of simulated and measured intensity corrected human brain data sets indicates the best performance utilizing the birdcage image (NRMSE = 0.39, CSFout:CSFin = 1.00). However, employing a support region (NRMSE = 0.40, CSFout:CSFin = 1.17), a universal sensitivity map (NRMSE = 0.41, CSFout:CSFin = 1.05) or a pre-scanned sensitivity map (NRMSE = 0.42, CSFout:CSFin = 1.07) shows only slightly worse results.Conclusion: Acquiring a birdcage image as reference image to correct for the receive profile demonstrates the best performance. However, when aiming to reduce acquisition time or for measurements without existing birdcage coil, methods that use a support region as reference image, a universal or a pre-scanned sensitivity map provide good alternatives for correction of the receive profile.