Evaluating pH in the Extracellular Tumor Microenvironment Using CEST MRI and Other Imaging Methods

Figure 16

CEST MRI of tumor pHe with Yb-DO3A-oAA. (a) The CEST spectrum of Yb-DO3A-oAA was fitted with Lorentzian line shapes to measure two CEST effects. (b) A ratio of the CEST effects was linearly correlated with pH. (c) The same CEST ratio was measured in a MCF-7 mammary carcinoma model after direct injection of the agent into the tumor tissue. (d) A map of extracellular pH (pHe) was determined from the map of the CEST ratio. (e) The pHe map was filtered to only retain results from pixels that had two statistically significant CEST amplitudes, resulting in a pHe map of the tumor and tube containing the agent (the other tube contained only water). Reproduced with permission from [57].

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