Centre of Functional and Metabolic Mapping, Robarts Research Institute, The University of Western Ontario, London, ON N6A 3K7, Canada.
Department of Biochemistry, Schulich School of Medicine and Dentistry, The University of Western Ontario, London, ON N6A 3K7, Canada.
Tomography. 2022 Mar 9;8(2):730-739. doi: 10.3390/tomography8020060.
Many pathological conditions lead to altered intracellular pH (pH) disrupting normal cellular functions. The chemical exchange saturation transfer (CEST) method, known as Amine and Amide Concentration Independent Detection (AACID), can produce image contrast that is predominantly dependent on tissue intracellular pH. The AACID value is linearly related to the ratio of the 3.5 ppm amide CEST effect and the 2.75 ppm amine CEST effect in the physiological range. However, the amine CEST effect at 2 ppm is often more clearly defined in vivo, and may provide greater sensitivity to pH changes. The purpose of the current study was to compare AACID measurement precision utilizing the 2.0 and 2.75 ppm amine CEST effects. We hypothesized that the 2.0 ppm amine CEST resonance would produce measurements with greater sensitivity to pH . In the current study, we compare the range of the AACID values obtained in 24 mice with brain tumors and in normal tissue using the 2 ppm and 2.75 ppm amine resonances. All CEST data were acquired on a 9.4T MRI scanner. The AACID measurement range increased by 39% when using the 2 ppm amine resonance compared to the 2.75 ppm resonance, with decreased measurement variability across the brain. These data indicate that in vivo pH measurements made using AACID CEST can be enhanced by incorporating the 2 ppm amine resonance. This approach should be considered for pH measurements made over short intervals when no changes are expected in the concentration of metabolites that contribute to the 2 ppm amine resonance.
许多病理状况会导致细胞内 pH 值改变（pH），从而破坏正常的细胞功能。化学交换饱和转移（CEST）方法，称为胺和酰胺浓度独立检测（AACID），可以产生主要依赖于组织细胞内 pH 值的图像对比。AACID 值与生理范围内 3.5 ppm 酰胺 CEST 效应与 2.75 ppm 胺 CEST 效应的比值呈线性相关。然而，在体内，2 ppm 处的胺 CEST 效应通常更为明显，并且可能对 pH 变化具有更高的敏感性。本研究的目的是比较利用 2.0 和 2.75 ppm 胺 CEST 效应进行 AACID 测量精度。我们假设 2.0 ppm 胺 CEST 共振将产生对 pH 变化更敏感的测量值。在目前的研究中，我们比较了使用 2 ppm 和 2.75 ppm 胺共振在 24 只患有脑肿瘤的小鼠和正常组织中获得的 AACID 值范围。所有 CEST 数据均在 9.4T MRI 扫描仪上采集。与使用 2.75 ppm 胺共振相比，使用 2 ppm 胺共振时，AACID 测量范围增加了 39%，并且大脑内的测量变异性降低。这些数据表明，通过合并 2 ppm 胺共振，可以增强使用 AACID CEST 进行的体内 pH 测量。当预计没有参与 2 ppm 胺共振的代谢物浓度发生变化时，这种方法应该考虑用于短时间间隔内的 pH 测量。
