Centre for Functional Magnetic Resonance Imaging of the Brain, University of Oxford, Oxford, UK.
Magn Reson Med. 2013 Dec;70(6):1682-9. doi: 10.1002/mrm.24623. Epub 2013 Feb 7.
To examine the effects of the reconstruction algorithm of magnitude images from multichannel diffusion MRI on fiber orientation estimation.
It is well established that the method used to combine signals from different coil elements in multichannel MRI can have an impact on the properties of the reconstructed magnitude image. Using a root-sum-of-squares approach results in a magnitude signal that follows an effective noncentral-χ distribution. As a result, the noise floor, the minimum measurable in the absence of any true signal, is elevated. This is particularly relevant for diffusion-weighted MRI, where the signal attenuation is of interest.
In this study, we illustrate problems that such image reconstruction characteristics may cause in the estimation of fiber orientations, both for model-based and model-free approaches, when modern 32-channel coils are used. We further propose an alternative image reconstruction method that is based on sensitivity encoding (SENSE) and preserves the Rician nature of the single-channel, magnitude MR signal. We show that for the same k-space data, root-sum-of-squares can cause excessive overfitting and reduced precision in orientation estimation compared with the SENSE-based approach.
These results highlight the importance of choosing the appropriate image reconstruction method for tractography studies that use multichannel receiver coils for diffusion MRI acquisition.
探讨从多通道扩散 MRI 重建幅度图像的重建算法对纤维方向估计的影响。
众所周知，多通道 MRI 中组合不同线圈元件信号的方法会对重建幅度图像的特性产生影响。采用均方根和方法会导致幅度信号遵循有效的非中心 χ 分布。因此，噪声基底（在没有任何真实信号的情况下可测量的最小值）升高。这对于扩散加权 MRI 特别相关，因为信号衰减是感兴趣的。
在这项研究中，我们说明了在使用现代 32 通道线圈时，这种图像重建特征可能会导致纤维方向估计中出现的问题，无论是基于模型的方法还是无模型的方法。我们进一步提出了一种替代的图像重建方法，该方法基于灵敏度编码（SENSE）并保留单通道幅度 MR 信号的瑞利性质。我们表明，对于相同的 k 空间数据，与基于 SENSE 的方法相比，均方根和方法会导致过度拟合和方向估计精度降低。
这些结果强调了在使用多通道接收线圈进行扩散 MRI 采集的示踪研究中选择适当的图像重建方法的重要性。
