pH imaging. A review of pH measurement methods and applications in cancers.
pH imaging. A review of pH measurement methods and applications in cancers.
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发表时间：
2004
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通讯作者：
R. Gillies;N. Raghunand;M. García-Martín;R. Gatenby
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作者：
R. Gillies;N. Raghunand;M. García-Martín;R. Gatenby
酸碱平衡在多种常见疾病中发生改变，包括慢性阻塞性肺病、缺血、肾功能衰竭和癌症。由于强大的细胞pH稳态机制，大多数pH的病理改变都表现为细胞外系统pH的变化。有数据表明，pH的改变不仅仅是代谢或生理失衡的附带现象，而且慢性pH改变可能有重要的后遗症。核磁共振成像和核磁共振成像测量表明，在1厘米距离内可以存在高达1.0 pH单位的pH梯度。虽然测量血液pH值可以提示全身性问题，但它不能精确定位病变或定量评估与正常pHe偏离的程度。因此，有必要开发具有高时空分辨率的pHe测量方法。目前研究的两种主要方法包括磁化转移法和弛豫法。ph依赖性MT效应可以通过内源性信号或外源性CEST试剂观察到。虽然内源性信号具有完全无创和相对直接应用的优势，但它们缺乏未来CEST试剂可能提供的完整的生物物理特征和动态范围。ph依赖性弛豫也需要注射或输注外源性对比剂。在MT和松弛成像方法中，效果的大小以及量化pHe的能力取决于CR在空间和时间上的浓度变化。已经提出了许多方法来解决这个问题，一旦解决了这个问题，pH成像方法将适用于人类临床病理。
Acid-base balance is altered in a variety of common pathologies, including COPD, ischemia, renal failure, and cancer. Because of robust cellular pH homeostatic mechanisms, most of the pathological alterations in pH are expressed as changes in the extracellular, systemic pH. There are data to indicate that altered pH is not simply an epiphenomenon of metabolic or physiologic imbalance but that chronic pH alterations can have important sequelae. MRSI and MRI measurements indicate that pH gradients of up to 1.0 pH unit can exit within 1-cm distance. Although measurement of blood pH can indicate systemic problems, it cannot pinpoint the lesion or quantitatively assess the magnitude of excursion from normal pHe. Hence, there is a need to develop pHe measurement methods with high spatiotemporal resolution. The two major approaches being investigated include magnetization transfer methods and relaxation methods. pH-dependent MT effects can observed with endogenous signals or exogenously applied CEST agents. While endogenous signals have the advantage of being fully noninvasive and relatively straightforward to apply, they lack a full biophysical characterization and dynamic range that might be afforded by future CEST agents. pH-dependent relaxivity also requires the injection or infusion of exogenous contrast reagents. In both MT and relaxographic approaches, the magnitude of the effect, and, thus, the ability to quantify pHe, depends on a spatially and temporally varying concentration of the CR. A number of approaches have been proposed to solve this problem and, once it is solved, pH imaging methods will be applicable to human clinical pathologies.