Deoni Sean C L, Rutt Brian K, Peters Terry M
Centre for Neuroimaging Sciences, Institute of Psychiatry, Box P089, London SE5 8AF, UK.
Magn Reson Imaging. 2006 Nov;24(9):1241-8. doi: 10.1016/j.mri.2006.03.015. Epub 2006 Sep 18.
The increased use of phased-array and surface coils in magnetic resonance imaging, the push toward increased field strength and the need for standardized imaging across multiple sites during clinical trials have resulted in the need for methods that can ensure consistency of intensity both within the image and across multiple subjects/sites. Here, we describe a means of addressing these concerns through an extension of the rapid T(1) mapping technique - driven equilibrium single-pulse observation of T(1). The effectiveness of the proposed approach was evaluated using human brain T(1) maps acquired at 1.5 T with a multichannel phased-array coil. Corrected "synthetic" T(1)-weighted images were reconstructed by substituting the T(1) values back into the governing signal intensity equation while assuming a constant value for the equilibrium magnetization. To demonstrate signal normalization across a longitudinal study, we calculated synthetic T(1)-weighted images from data acquired from the same healthy subject at four different time points. Signal intensity profiles between the acquired and synthetic images were compared to determine the improvements with our proposed approach. Following correction, the images demonstrate obvious qualitative improvement with increased signal uniformity across the image. Near-perfect signal normalization was also observed across the longitudinal study, allowing direct comparison between the images. In addition, we observe an increase in contrast-to-noise ratio (compared with regular T(1)-weighted images) for synthetic images created, assuming uniform proton density throughout the volume. The proposed approach permits rapid correction for signal intensity inhomogeneity without significantly lengthening exam time or reducing image signal-to-noise ratio. This technique also provides a robust method for signal normalization, which is useful in multicenter longitudinal MR studies of disease progression, and allows the user to reconstruct T(1)-weighted images with arbitrary T(1) weighting.
磁共振成像中相控阵线圈和表面线圈的使用增加、场强提升的趋势以及临床试验期间跨多个位点进行标准化成像的需求，导致需要能够确保图像内部以及多个受试者/位点之间强度一致性的方法。在此，我们描述了一种通过扩展快速T(1)映射技术——驱动平衡单脉冲T(1)观测来解决这些问题的方法。使用在1.5T下通过多通道相控阵线圈采集的人脑T(1)图谱评估了所提出方法的有效性。通过将T(1)值代入控制信号强度方程，同时假设平衡磁化强度为恒定值，重建校正后的“合成”T(1)加权图像。为了证明在纵向研究中的信号归一化，我们从同一健康受试者在四个不同时间点采集的数据计算合成T(1)加权图像。比较采集图像和合成图像之间的信号强度剖面，以确定我们提出的方法的改进效果。校正后，图像在定性上有明显改善，整个图像的信号均匀性增加。在纵向研究中还观察到近乎完美的信号归一化，允许图像之间进行直接比较。此外，对于假设整个体积内质子密度均匀而创建的合成图像，我们观察到对比噪声比有所增加（与常规T(1)加权图像相比）。所提出的方法允许快速校正信号强度不均匀性，而不会显著延长检查时间或降低图像信噪比。该技术还提供了一种强大的信号归一化方法，这在疾病进展的多中心纵向磁共振研究中很有用，并且允许用户重建具有任意T(1)加权的T(1)加权图像。
