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

Figure 11

Hyperpolarized ¹³C MR spectroscopic imaging of tumor pHe. (a) ¹³C MR spectroscopy was used to measure the ratio of [H¹³CO₃]/[¹³CO₂], which was used to calculate pH based on the Henderson-Hasselbalch equation, pH = pKa + log₁₀([H¹³CO₃]/[¹³CO₂]). (b) A solid line shows the correlation of the pH values determined from ¹³C MRS and an electrode. The dashed line representing equal measurements is provided as a visual reference. (c) A subcutaneously implanted EL4 tumor in a mouse is outlined in red in an axial MR image. (d) The pH map of the same mouse calculated from ¹³C MR spectroscopic imaging. The tumor margin is outlined in white. Reproduced with permission from [48].

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