Quantifying MRI frequency shifts due to structures with anisotropic magnetic susceptibility using pyrolytic graphite sheet
Quantifying MRI frequency shifts due to structures with anisotropic magnetic susceptibility using pyrolytic graphite sheet
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DOI：
10.1038/s41598-018-24650-2
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发表时间：
2018-04-19
影响因子：
4.6
通讯作者：
Bowtell, Richard
中科院分区：
文献类型：
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作者：
Cronin, Matthew J.;Bowtell, Richard
磁化率是磁共振成像（MRI）中重要的对比来源，组织磁化率的空间变化会影响测量信号的幅度和相位。这种对比通常通过假设组织具有各向同性磁化率来解释，但最近的工作表明，有序生物组织（如髓鞘神经和心肌纤维）的各向异性磁化率会产生意想不到的图像对比度。这种现象的发生是因为由各向异性磁化率材料形成的微结构元素所产生的场变化模式可能与根据各向同性磁化率模拟所预测的结果大不相同。在组织的MR图像中，这些元素在亚体素长度尺度上表现出来，因此它们产生的场变化模式不能直接可视化。在这里，我们使用具有较大磁化率各向异性的热解石墨片形成已知几何形状的结构，其尺寸足够大，可以直接使用MRI绘制场变化模式。这允许直接验证描述具有生物学相关形状（板、球壳和圆柱壳）的各向异性结构的场变化模式的理论表达式。
Magnetic susceptibility is an important source of contrast in magnetic resonance imaging (MRI), with spatial variations in the susceptibility of tissue affecting both the magnitude and phase of the measured signals. This contrast has generally been interpreted by assuming that tissues have isotropic magnetic susceptibility, but recent work has shown that the anisotropic magnetic susceptibility of ordered biological tissues, such as myelinated nerves and cardiac muscle fibers, gives rise to unexpected image contrast. This behavior occurs because the pattern of field variation generated by microstructural elements formed from material of anisotropic susceptibility can be very different from that predicted by modelling the effects in terms of isotropic susceptibility. In MR images of tissue, such elements are manifested at a sub-voxel length-scale, so the patterns of field variation that they generate cannot be directly visualized. Here, we used pyrolytic graphite sheet which has a large magnetic susceptibility anisotropy to form structures of known geometry with sizes large enough that the pattern of field variation could be mapped directly using MRI. This allowed direct validation of theoretical expressions describing the pattern of field variation from anisotropic structures with biologically relevant shapes (slabs, spherical shells and cylindrical shells).