Department of Medical Biophysics, Schulich School of Medicine & Dentistry, Western University, London, Ontario, Canada.
Centre for Functional and Metabolic Mapping, Robarts Research Institute, Schulich School of Medicine & Dentistry, Western University, London, Ontario, Canada.
NMR Biomed. 2024 May;37(5):e5103. doi: 10.1002/nbm.5103. Epub 2024 Jan 19.
Spinal cord ischemia and hypoxia can be caused by compression, injury, and vascular alterations. Measuring ischemia and hypoxia directly in the spinal cord noninvasively remains challenging. Ischemia and hypoxia alter tissue pH, providing a physiologic parameter that may be more directly related to tissue viability. Chemical exchange saturation transfer (CEST) is an MRI contrast mechanism that can be made sensitive to pH. More specifically, amine/amide concentration independent detection (AACID) is a recently developed endogenous CEST contrast that has demonstrated sensitivity to intracellular pH at 9.4 T. The goal of this study was to evaluate the reproducibility of AACID CEST measurements at different levels of the healthy cervical spinal cord at 3.0 T incorporating B correction. Using a 3.0 T MRI scanner, two 3D CEST scans (saturation pulse train followed by a 3D snapshot gradient-echo readout) were performed on 12 healthy subjects approximately 10 days apart, with the CEST volume centered at the C4 level for all subjects. Scan-rescan reproducibility was evaluated by examining between and within-subject coefficients of variation (CVs) and absolute AACID value differences. The C4 level of the spinal cord demonstrated the lowest within-subject CVs (4.1%-4.3%), between-subject CVs (5.6%-6.3%), and absolute AACID percent difference (5.8-6.1%). The B correction scheme significantly improved reproducibility (adjusted p-value = 0.002) compared with the noncorrected data, suggesting that implementing B corrections in the spinal cord is beneficial. It was concluded that pH-weighted AACID measurements, incorporating B-inhomogeneity correction, were reproducible within subjects along the healthy cervical spinal cord and that optimal image quality was achieved at the center of the 3D CEST volume.
脊髓缺血和缺氧可由压迫、损伤和血管改变引起。直接无创测量脊髓的缺血和缺氧仍然具有挑战性。缺血和缺氧会改变组织 pH 值，提供一个可能与组织活力更直接相关的生理参数。化学交换饱和传递（CEST）是一种 MRI 对比机制，可以使其对 pH 值敏感。更具体地说，胺/酰胺浓度独立检测（AACID）是一种最近开发的内源性 CEST 对比技术，已证明在 9.4 T 时对细胞内 pH 值敏感。本研究的目的是评估在 3.0 T 下使用 B 校正时，健康颈段脊髓不同水平的 AACID CEST 测量的可重复性。使用 3.0 T MRI 扫描仪，对 12 名健康受试者进行了两次 3D CEST 扫描（饱和脉冲链，随后进行 3D 快照梯度回波读出），CEST 体积在所有受试者的 C4 水平处居中。通过检查受试者内和受试者间的变异系数（CV）和绝对 AACID 值差异，评估扫描-重扫的可重复性。脊髓 C4 水平表现出最低的受试者内 CV（4.1%-4.3%）、受试者间 CV（5.6%-6.3%）和绝对 AACID 百分比差异（5.8-6.1%）。B 校正方案与未校正数据相比显著提高了可重复性（校正 p 值=0.002），这表明在脊髓中实施 B 校正有益。研究得出结论，在健康颈段脊髓内，包含 B 不均匀性校正的 pH 加权 AACID 测量具有可重复性，并且在 3D CEST 体积的中心获得了最佳的图像质量。
