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. 2022 Dec;88(6):2475-2484. doi: 10.1002/mrm.29409. Epub 2022 Aug 15.
Ultra-high field MR imaging lacks B inhomogeneity due to shorter RF wavelengths used at higher field strengths compared to human anatomy. CEST techniques tend to be highly susceptible to B inhomogeneities due to a high and uniform B field being necessary to create the endogenous contrast. High-permittivity dielectric pads have seen increasing usage in MR imaging due to their ability to tailor the spatial distribution of the B field produced. The purpose of this work is to demonstrate that dielectric materials can be used to improve glutamate weighted CEST (gluCEST) at 7T.
GluCEST images were acquired on a 7T system on six healthy volunteers. Aqueous calcium titanate pads, with a permittivity of approximately 110, were placed on either side in the subject's head near the temporal lobes. A post-processing correction algorithm was implemented in combination with dielectric padding to compare contrast improvement. Tissue segmentation was performed to assess the effect of dielectric pads on gray and white matter separately.
GluCEST images demonstrated contrast enhancement in the lateral temporal lobe regions with dielectric pad placement. Tissue segmentation analysis showed an increase in correction effectiveness within the gray matter tissue compared to white matter tissue. Statistical testing suggested a significant difference in gluCEST contrast when pads were used and showed a difference in the gray matter tissue segment.
The use of dielectric pads improved the B field homogeneity and enhanced gluCEST contrast for all subjects when compared to data that did not incorporate padding.
与人体解剖结构相比，超高磁场磁共振成像由于使用了较短的射频波长，因此缺乏 B 不均匀性。由于需要高且均匀的 B 场来产生内源性对比，CEST 技术往往非常容易受到 B 不均匀性的影响。由于高介电常数介电垫能够调整所产生的 B 场的空间分布，因此在磁共振成像中越来越多地使用它们。本研究旨在证明介电材料可用于改善 7T 下的谷氨酸加权 CEST（gluCEST）。
在 7T 系统上对 6 名健康志愿者进行了 gluCEST 图像采集。将介电常数约为 110 的水性钛酸钙垫放置在颞叶附近受试者头部的两侧。实现了一种后处理校正算法，结合介电垫进行对比增强比较。进行组织分割以分别评估介电垫对灰质和白质的影响。
介电垫放置后，gluCEST 图像显示外侧颞叶区域的对比度增强。组织分割分析显示，与白质组织相比，灰质组织中的校正效果有所提高。统计测试表明，与未使用衬垫的数据相比，当使用衬垫时，gluCEST 对比度有显著差异，并且灰质组织部分也有差异。
与不包含衬垫的数据相比，使用介电垫可以改善 B 场均匀性，并增强所有受试者的 gluCEST 对比度。
