多回波 T2 磁共振图像的时相校正。

Temporal phase correction of multiple echo T2 magnetic resonance images.

机构信息

Diagnostic Imaging Services, Interior Health, Kelowna, Canada.

出版信息

J Magn Reson. 2013 Jun;231:22-31. doi: 10.1016/j.jmr.2013.02.019. Epub 2013 Mar 16.

Abstract

Typically, magnetic resonance imaging (MRI) analysis is performed on magnitude data, and multiple echo T2 data consist of numerous images of the same slice taken with different echo spacing, giving voxel-wise temporal sampling of the noise as the signals decay according to T2 relaxation. Magnitude T2 decay data has Rician distributed noise which is characterized by a change in the noise distribution from Gaussian, through a transitional region, to Rayleigh as the signal to noise ratio decreases with increasing echo time. Non-Gaussian noise distributions may produce errors in the commonly applied non-negative least squares (NNLS) algorithm that is used to assess multiple echo decays for compartmentalized water environments through the creation of T2 distributions. Typically, Gaussian noise is sought by performing spatial-based phase correction on the MRI data however, these methods cannot capitalize on the temporal information available from multiple echo T2 acquisitions. Here we describe a temporal phase correction (TPC) algorithm that utilizes the temporal noise information available in multiple echo T2 acquisitions to put the relevant decay information in the Real portion of the decay data and leave only noise in the Imaginary portion. We apply this TPC algorithm to create real-valued multiple echo T2 data from human subjects measured at 1.5 T. We show that applying TPC causes changes in the T2 distribution estimates; notably the possible resolution of separate extracellular and intracellular water environments, and the disappearance of the commonly labeled cerebrospinal fluid peak, which might be an artefact observed in many previously published multiple echo T2 analyses.

摘要

通常情况下,磁共振成像(MRI)分析是基于幅度数据进行的,而多回波 T2 数据由同一切片上用不同回波间隔拍摄的许多图像组成,根据 T2 弛豫,随着信号衰减,为每个体素提供了噪声的时间采样。幅度 T2 衰减数据具有瑞利分布噪声,其特征是随着信噪比随回波时间的增加而降低,噪声分布从高斯分布通过过渡区变为瑞利分布。非高斯噪声分布可能会导致常用的非负最小二乘法(NNLS)算法出现误差,该算法用于通过创建 T2 分布来评估分室水环境的多回波衰减。通常,通过对 MRI 数据进行基于空间的相位校正来寻找高斯噪声,但是这些方法无法利用多回波 T2 采集提供的时间信息。在这里,我们描述了一种时间相位校正(TPC)算法,该算法利用多回波 T2 采集提供的时间噪声信息,将相关的衰减信息置于衰减数据的实部中,并仅在虚部中保留噪声。我们将此 TPC 算法应用于从 1.5T 测量的人体中创建实值多回波 T2 数据。我们表明,应用 TPC 会导致 T2 分布估计的变化;特别是可能可以分辨出细胞外和细胞内水环境的分离,以及通常标记的脑脊液峰的消失,这可能是许多先前发表的多回波 T2 分析中观察到的一种伪影。

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