Center for Advanced Metabolic Imaging in Precision Medicine, Department of Radiology, University of Pennsylvania, Philadelphia, Pennsylvania, USA.
Penn Statistics in Imaging and Visualization Center, Department of Biostatistics, Epidemiology, and Informatics, University of Pennsylvania, Philadelphia, Pennsylvania, USA.
Magn Reson Med. 2023 Oct;90(4):1537-1546. doi: 10.1002/mrm.29739. Epub 2023 Jun 6.
Nuclear Overhauser effect magnetization transfer ratio (NOE ) is a technique used to investigate brain lipids and macromolecules in greater detail than other techniques and benefits from increased contrast at 7 T. However, this contrast can become degraded because of inhomogeneities present at ultra-high field strengths. High-permittivity dielectric pads (DP) have been used to correct for these inhomogeneities via displacement currents generating secondary magnetic fields. The purpose of this work is to demonstrate that dielectric pads can be used to mitigate inhomogeneities and improve NOE contrast in the temporal lobes at 7 T.
Partial 3D NOE contrast images and whole brain field maps were acquired on a 7 T MRI across six healthy subjects. Calcium titanate DP, having a relative permittivity of 110, was placed next to the subject's head near the temporal lobes. Pad corrected NOE images had a separate postprocessing linear correction applied.
DP provided supplemental to the temporal lobes while also reducing the magnitude across the posterior and superior regions of the brain. This resulted in a statistically significant increase in NOE contrast in substructures of the temporal lobes both with and without linear correction. The padding also produced a convergence in NOE contrast toward approximately equal mean values.
NOE images showed significant improvement in temporal lobe contrast when DP were used, which resulted from an increase in homogeneity across the entire brain slab. DP-derived improvements in NOE are expected to increase the robustness of the brain substructural measures both in healthy and pathological conditions.
核 Overhauser 效应磁化转移率（NOE）是一种用于比其他技术更详细地研究脑脂质和大分子的技术，其在 7T 时具有更高的对比度优势。然而，这种对比度可能会因超高场强下存在的不均匀性而降低。高介电常数的电介质垫（DP）已被用于通过产生二次磁场的位移电流来校正这些不均匀性。本工作的目的是证明电介质垫可以用于减轻 7T 时颞叶的不均匀性并提高 NOE 对比度。
在 7T MRI 上对 6 名健康受试者进行了部分 3D NOE 对比图像和全脑 场图采集。将具有相对介电常数 110 的钛酸钙 DP 放置在靠近颞叶的受试者头部旁边。垫校正后的 NOE 图像应用了单独的后处理线性校正。
DP 为颞叶提供了额外的 ，同时还降低了大脑后部和上部区域的 幅度。这导致颞叶亚结构的 NOE 对比度在有和没有线性校正的情况下都有统计学意义的增加。填充还导致 NOE 对比度趋于接近相等的平均值。
当使用 DP 时，NOE 图像显示颞叶对比度有显著改善，这是由于整个脑板的均匀性增加所致。DP 对 NOE 的改进预计将增加健康和病理条件下脑亚结构测量的稳健性。
