Fujimoto Kyoko, Polimeni Jonathan R, van der Kouwe André J W, Reuter Martin, Kober Tobias, Benner Thomas, Fischl Bruce, Wald Lawrence L
Athinoula A. Martinos Center for Biomedical Imaging, Massachusetts General Hospital, 149 13th Street, Suite 2301, Charlestown, MA 02129, USA.
Athinoula A. Martinos Center for Biomedical Imaging, Massachusetts General Hospital, 149 13th Street, Suite 2301, Charlestown, MA 02129, USA; Department of Radiology, Harvard Medical School, 55 Fruit St, Boston, MA 02114, USA.
Neuroimage. 2014 Apr 15;90:60-73. doi: 10.1016/j.neuroimage.2013.12.012. Epub 2013 Dec 15.
The Magnetization-Prepared 2 Rapid Acquisition Gradient Echo (MP2RAGE) method achieves spatially uniform contrast across the entire brain between gray matter and surrounding white matter tissue and cerebrospinal fluid by rapidly acquiring data at two points during an inversion recovery, and then combining the two volumes so as to cancel out sources of intensity and contrast bias, making it useful for neuroimaging studies at ultrahigh field strengths (≥7T). To quantify the effectiveness of the MP2RAGE method for quantitative morphometric neuroimaging, we performed tissue segmentation and cerebral cortical surface reconstruction of the MP2RAGE data and compared the results with those generated from conventional multi-echo MPRAGE (MEMPRAGE) data across a group of healthy subjects. To do so, we developed a preprocessing scheme for the MP2RAGE image data to allow for automatic cortical segmentation and surface reconstruction using FreeSurfer and analysis methods to compare the positioning of the surface meshes. Using image volumes with 1mm isotropic voxels we found a scan-rescan reproducibility of cortical thickness estimates to be 0.15 mm (or 6%) for the MEMPRAGE data and a slightly lower reproducibility of 0.19 mm (or 8%) for the MP2RAGE data. We also found that the thickness estimates were systematically smaller in the MP2RAGE data, and that both the interior and exterior cortical boundaries estimated from the MP2RAGE data were consistently positioned within the corresponding boundaries estimated from the MEMPRAGE data. Therefore several measureable differences exist in the appearance of cortical gray matter and its effect on automatic segmentation methods that must be considered when choosing an acquisition or segmentation method for studies requiring cortical surface reconstructions. We propose potential extensions to the MP2RAGE method that may help to reduce or eliminate these discrepancies.
磁化准备快速采集梯度回波（MP2RAGE）方法通过在反转恢复过程中的两个时间点快速采集数据，然后将这两个容积数据进行合并，以消除强度和对比度偏差的来源，从而在整个大脑中实现灰质与周围白质组织及脑脊液之间的空间均匀对比度，这使得该方法在超高场强（≥7T）的神经成像研究中非常有用。为了量化MP2RAGE方法在定量形态学神经成像中的有效性，我们对MP2RAGE数据进行了组织分割和大脑皮质表面重建，并将结果与一组健康受试者的传统多回波MPRAGE（MEMPRAGE）数据生成的结果进行了比较。为此，我们开发了一种针对MP2RAGE图像数据的预处理方案，以便使用FreeSurfer进行自动皮质分割和表面重建，并采用分析方法来比较表面网格的定位。使用具有1mm各向同性体素的图像容积，我们发现MEMPRAGE数据的皮质厚度估计的扫描-重扫重复性为0.15mm（或6%），而MP2RAGE数据的重复性略低，为0.19mm（或8%）。我们还发现，MP2RAGE数据中的厚度估计值系统性地较小，并且从MP2RAGE数据估计的皮质内外边界始终位于从MEMPRAGE数据估计的相应边界内。因此，在皮质灰质的外观及其对自动分割方法的影响方面存在几个可测量的差异，在为需要皮质表面重建的研究选择采集或分割方法时必须予以考虑。我们提出了对MP2RAGE方法的潜在扩展，这可能有助于减少或消除这些差异。
