Vanderbilt University Institute of Imaging Science, Vanderbilt University Medical Center, USA; Department of Radiology and Radiological Sciences, Vanderbilt University Medical Center, TN, USA.
Vanderbilt University Institute of Imaging Science, Vanderbilt University Medical Center, USA; Department of Biomedical Engineering, Vanderbilt University, TN, USA.
Neuroimage Clin. 2021;30:102633. doi: 10.1016/j.nicl.2021.102633. Epub 2021 Mar 23.
The sensitivity and accuracy of chemical exchange saturation transfer (CEST) and nuclear Overhauser enhancement (NOE) effects for assessing injury-associated changes in cervical spinal cords were evaluated in squirrel monkeys. Multiple interacting pools of protons, including one identified by an NOE at -1.6 ppm relative to water (NOE(-1.6)), were derived and quantified from fitting proton Z-spectra. The effects of down-sampled data acquisitions and corrections for non-specific factors including T, semi-solid magnetization transfer, and direct saturation of free water (DS), were investigated. The overall goal is to develop a protocol for rapid data acquisition for assessing the molecular signatures of the injured spinal cord and its surrounding regions.
MRI scans were recorded of anesthetized squirrel monkeys at 9.4 T, before and after a unilateral dorsal column sectioning of the cervical spinal cord. Z-spectral images at 51 different RF offsets were acquired. The amplitudes of CEST and NOE effects from multiple proton pools were quantified using a six-pool Lorenzian fitting of each Z-spectrum (MTR). In addition, down-sampled data using reduced selections of RF offsets were analyzed and compared. An apparent exchange-dependent relaxation (AREX) method was also used to correct for non-specific factors in quantifying regional spectra around lesion sites.
The parametric maps from multi-pool fitting using the complete sampling data (P51e) detected unilateral changes at and around the injury. The maps derived from selected twofold down-sampled data with appropriate interpolation (P26sI51) revealed quite similar spatial distributions of different pools as those obtained using P51e at each resonance shift. Across 10 subjects, both data acquisition schemes detected significant decreases in NOE(-3.5) and NOE(-1.6) and increases in DS(0.0) and CEST(3.5) at the lesion site relative to measures of the normal tissues before injury. AREX of cysts and other abnormal tissues at and around the lesion site also exhibited significant changes, especially at 3.5, -1.6 and -3.5 ppm RF offsets.
These results confirm that a reduced set of RF offsets and down sampling are adequate for CEST imaging of injured spinal cord and allow shorter imaging times and/or permit additional signal averaging. AREX correction improved the accuracy of CEST and NOE measures. The results provide a rapid (~13 mins), sensitive, and accurate protocol for deriving multiple NOE and CEST effects simultaneously in spinal cord imaging at high field.
评估化学交换饱和传递（CEST）和核 Overhauser 增强（NOE）效应对评估颈脊髓损伤相关变化的敏感性和准确性。从拟合质子 Z 谱中得出并量化了多个相互作用的质子池，包括一个相对于水（NOE（-1.6））为-1.6 ppm 的 NOE。研究了下采样数据采集和校正的影响，包括 T、半固态磁化转移和自由水的直接饱和（DS）等非特异性因素。总体目标是开发一种快速数据采集协议，用于评估损伤脊髓及其周围区域的分子特征。
在 9.4 T 下对麻醉的松鼠猴进行 MRI 扫描，在单侧颈脊髓背柱切开前后进行。在 51 个不同的 RF 偏移处采集 Z 光谱图像。使用每个 Z 谱的六池洛伦兹拟合（MTR）定量来自多个质子池的 CEST 和 NOE 效应的幅度。此外，还分析并比较了使用 RF 偏移减少选择的下采样数据。还使用表观交换相关弛豫（AREX）方法来校正定量病变部位周围区域谱中的非特异性因素。
使用完整采样数据（P51e）的多池拟合的参数图检测到损伤处和周围的单侧变化。使用适当插值的两折下采样数据（P26sI51）得出的图谱揭示了不同池的空间分布与使用 P51e 在每个共振位移处获得的图谱非常相似。在 10 个受试者中，两种数据采集方案都在损伤部位检测到 NOE（-3.5）和 NOE（-1.6）的显著降低，以及 DS（0.0）和 CEST（3.5）的显著增加与损伤前正常组织的测量值相比。病变部位及其周围的囊肿和其他异常组织的 AREX 也显示出显著变化，特别是在 3.5、-1.6 和-3.5 ppm RF 偏移处。
这些结果证实，减少的 RF 偏移集和下采样对于受伤脊髓的 CEST 成像足够充分，允许更短的成像时间和/或允许额外的信号平均。AREX 校正提高了 CEST 和 NOE 测量的准确性。结果提供了一种快速（~13 分钟）、敏感和准确的方案，用于在高场脊髓成像中同时获得多个 NOE 和 CEST 效应。
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