High-resolution three-dimensional macromolecular proton fraction mapping for quantitative neuroanatomical imaging of the rodent brain in ultra-high magnetic fields.
High-resolution three-dimensional macromolecular proton fraction mapping for quantitative neuroanatomical imaging of the rodent brain in ultra-high magnetic fields.
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DOI：
10.1016/j.neuroimage.2016.09.036
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发表时间：
2017-02-15
期刊：
影响因子：
5.7
通讯作者：
Yarnykh VL
中科院分区：
文献类型：
--
作者：
Naumova AV;Akulov AE;Khodanovich MY;Yarnykh VL
超高场MRI的一个众所周知的问题是生成高分辨率的三维图像，以详细表征白质和灰质解剖结构。传统上用于此目的的t1加权成像随着磁场强度的增加，白质和灰质之间的对比度下降。大分子质子分数（MPF）作图是一种新的方法，有可能缓解这一问题，因为它具有较强的髓鞘对比和磁场强度参数的独立性。MPF是决定组织中磁化转移效应的关键参数，在双池模型中被定义为参与与水质子磁化交换的大分子质子的相对数量。本研究的目的是表征超高磁场下脑组织的双池模型参数，并引入快速高场3D强积金成像作为小动物应用的解剖和定量神经成像模式。使用11.7T动物MRI扫描仪获得4只成年雄性大鼠的体内成像数据。综合比较标准R1图和T2图的脑组织对比度，并从z光谱图像重建两池模型参数图，包括池的MPF、交叉松弛速率常数和T2。此外，采用单点综合参考方法获得了各向同性170 μm体素大小的高分辨率全脑三维MPF图。MPF图显示，与其他参数相比，白质和灰质之间的对比增加了3 - 6倍。单点合成参比法测得的强积金值与z光谱法测得的强积金值吻合良好。在11.7T时，大鼠脑结构的强积金值与较低场强时相似，从而证实了强积金的场独立性。3D MPF映射为超高磁场下的神经成像提供了有用的工具，既可以基于髓磷脂含量的定量组织表征，又可以通过白质和灰质之间的高对比度实现高分辨率神经解剖可视化。
A well-known problem in ultra-high-field MRI is generation of high-resolution three-dimensional images for detailed characterization of white and gray matter anatomical structures. T1-weighted imaging traditionally used for this purpose suffers from the loss of contrast between white and gray matter with an increase of magnetic field strength. Macromolecular proton fraction (MPF) mapping is a new method potentially capable to mitigate this problem due to strong myelin-based contrast and independence of this parameter of field strength. MPF is a key parameter determining the magnetization transfer effect in tissues and defined within the two-pool model as a relative amount of macromolecular protons involved into magnetization exchange with water protons. The objectives of this study were to characterize the two-pool model parameters in brain tissues in ultra-high magnetic fields and introduce fast high-field 3D MPF mapping as both anatomical and quantitative neuroimaging modality for small animal applications. In vivo imaging data were obtained from four adult male rats using an 11.7T animal MRI scanner. Comprehensive comparison of brain tissue contrast was performed for standard R1 and T2 maps and reconstructed from Z-spectroscopic images two-pool model parameter maps including MPF, cross-relaxation rate constant, and T2 of pools. Additionally, high-resolution whole-brain 3D MPF maps were obtained with isotropic 170 μm voxel size using the single-point synthetic-reference method. MPF maps showed 3–6-fold increase in contrast between white and gray matter compared to other parameters. MPF measurements by the single-point synthetic reference method were in excellent agreement with the Z-spectroscopic method. MPF values in rat brain structures at 11.7T were similar to those at lower field strengths, thus confirming field independence of MPF. 3D MPF mapping provides a useful tool for neuroimaging in ultra-high magnetic fields enabling both quantitative tissue characterization based on the myelin content and high-resolution neuroanatomical visualization with high contrast between white and gray matter.