Asllani Iris, Borogovac Ajna, Brown Truman R
Department of Radiology, College of Physicians and Surgeons, Columbia University, New York, New York 10032, USA.
Magn Reson Med. 2008 Dec;60(6):1362-71. doi: 10.1002/mrm.21670.
Partial volume effects (PVE) are a consequence of limited spatial resolution in brain imaging. In arterial spin labeling (ASL) MRI, the problem is exacerbated by the nonlinear dependency of the ASL signal on magnetization contributions from each tissue within an imaged voxel. We have developed an algorithm that corrects for PVE in ASL imaging. The algorithm is based on a model that represents the voxel intensity as a weighted sum of pure tissue contribution, where the weighting coefficients are the tissue's fractional volume in the voxel. Using this algorithm, we were able to estimate cerebral blood flow (CBF) for gray matter (GM) and white matter (WM) independently. The average voxelwise ratio of GM to WM CBF was approximately 3.2, in good agreement with reports in the literature. As proof of concept, data from PVE-corrected method were compared with those from the conventional, PVE-uncorrected method. As hypothesized, the two yielded similar CBF values for voxels containing >95% GM and differed in proportion with the voxels' heterogeneity. More importantly, the GM CBF assessed with the PVE-corrected method was independent of the voxels' heterogeneity, implying that estimation of flow was unaffected by PVE. An example of application of this algorithm in motor-activation data is also given.
部分容积效应（PVE）是脑成像中空间分辨率有限的结果。在动脉自旋标记（ASL）磁共振成像中，由于ASL信号对成像体素内各组织磁化贡献的非线性依赖性，这个问题变得更加严重。我们开发了一种在ASL成像中校正PVE的算法。该算法基于一个模型，该模型将体素强度表示为纯组织贡献的加权和，其中加权系数是组织在体素中的分数体积。使用该算法，我们能够独立估计灰质（GM）和白质（WM）的脑血流量（CBF）。GM与WM CBF的平均体素比率约为3.2，与文献报道一致。作为概念验证，将PVE校正方法的数据与传统的、未校正PVE的方法的数据进行了比较。如所假设的，对于包含>95%GM的体素，两者产生相似的CBF值，并且与体素的异质性成比例地不同。更重要的是，用PVE校正方法评估的GM CBF与体素的异质性无关，这意味着血流估计不受PVE影响。还给出了该算法在运动激活数据中的应用示例。
