Quantification of voxel-wise total fibre density: Investigating the problems associated with track-count mapping
Quantification of voxel-wise total fibre density: Investigating the problems associated with track-count mapping
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DOI：
10.1016/j.neuroimage.2015.05.070
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发表时间：
2015-08-15
期刊：
影响因子：
5.7
通讯作者：
Connelly, Alan
中科院分区：
文献类型：
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作者：
Calamante, Fernando;Smith, Robert E.;Connelly, Alan
能够从扩散磁共振数据中提取有价值的生物学参数是局部白质轴突密度。轨道密度成像(TDI)似乎可以提供这种测量；然而，这一直是有争议的主题，主要是因为轨道计数量化对跟踪偏差和误差高度敏感。球面反卷积知情滤波轨迹图(SIFT)后处理方法最近被引入以最小化轨迹图偏差，从而提供了一种更具生物学意义的措施，可用于轨迹计数图(即TDI跟随SIFT)。SIFT后的TDI强度理想地对应于纤维取向分布(FOD)的方向平均值，该平均值对应于AFD框架内的总表观纤维密度(AFD(TOTAL))；事实上，AFD(TOTAL)提供了本地分辨率下的本地纤维密度的直接测量，而不依赖于纤维跟踪。在这项研究中，我们展示了与定量TDI调查相关的问题，这些问题可以通过使用SIFT处理或直接使用AFD(总)图来避免。我们还表征了TDI图(有和没有SIFT前处理)和AFD(总)图的对象内和对象间的重复性。结果表明，SIFT改善了TDI的定量特征，但仍远逊于AFD(TOTAL)参数本身的性质，因为后者不需要跟踪。虽然标准TDI在需要高解剖对比度的应用中可能更好，特别是在与超分辨率相结合时，以便在自然分辨率下对总道密度(即，没有道方向信息)进行体素定量，但总AFD图优于TDI或其他相关的道-计数图。不管磁道计数方法如何，应该注意的是，所有这些体素平均方法都会丢弃在AFD等特定纤维方法中保留的重要信息。(C)2015 Elsevier Inc.保留所有权利。
A biological parameter that would be valuable to be able to extract from diffusion MRI data is the local white matter axonal density. Track-density imaging (TDI) has been used as if it could provide such a measure; however, this has been the subject of controversy, primarily due to the fact that track-count quantitation is highly sensitive to tracking biases and errors. The spherical-deconvolution informed filtering of tractograms (SIFT) post-processing method was recently introduced to minimise tractography biases, and thus provides a more biologically meaningful measure that could be used in track-count mapping (i.e. TDI following SIFT). The TDI intensity following SIFT ideally corresponds to the orientational average of the fibre orientation distribution (FOD), which corresponds to the total Apparent Fibre Density (AFD(total)) within the AFD framework; in fact, AFD(total) provides a direct measure of local fibre density at native resolution that does not rely on fibre-tracking. In this study, we demonstrate problems associated with quantitative TDI investigations, which can be avoided by using SIFT processing or directly by using AFD(total) maps. We also characterise the intra-and inter-subject reproducibility of TDI maps (with and without SIFT pre-processing) and AFD(total) maps. It is shown that SIFT improves the quantitative characteristics of TDI, but is still vastly inferior to the properties of the AFD(total) parameter itself, because the latter does not require tracking. While standard TDI might be preferable in applications when high anatomical contrast is required, particularly when combined with super-resolution, for voxel-wise quantitation of total tract density (i.e. without tract orientation information) at native resolution, the total AFD maps are preferable to TDI or other related track-count maps. Regardless of the track-count measure, it should be noted that all of these voxel-averaged approaches discard important information that is retained in fibre-specific approaches such as AFD. (C) 2015 Elsevier Inc. All rights reserved.