Figure 3.

GlucoCEST MRI. (A) Chemical structure of glucose. (B) Z-spectra and MTR_asym spectra of glucose and its first-step metabolite glucose 6-phosphate, as compared to that of fructose 6-phosphate and fructose 6,1-biphosphate (Reprinted with permission from Ref [60]). (C) Overview of rate constants and contrast contributions (darker color = higher contrast; white is negligible contrast) for glucoCEST, ¹⁸FDG-PET, and contrast-enhanced MRI and CT in tumors. For glucoCEST, the glucose concentrations in vascular space and EES are comparable, but due to lower pH the EES has a higher signal contribution. Intracellular signal is very small to negligible due to rapid glycolysis. In PET, the signal is predominantly due to trapped intracellular phosphorylated FDG. For contrast-enhanced MR and CT, the agents occupy only plasma in blood and while they enter the interstitium, the EES concentration is generally lower than in plasma due to limited K^trans. Glucose, on the other hand moves freely into the interstitium and the erythrocytes. v = vascular (plasma + erythrocytes), p = plasma. Reprinted with permission from Ref [61].