Figure 1.

Schematic representation of chemical exchange saturation transfer (CEST): (A-D) Diagrams of the metabolite of interest containing an amide group are shown with surrounding water molecules, for each step in the CEST saturation and exchange process. The water signal level corresponding to each subfigure is shown below each panel. (A) Before saturation. (B) Radiofrequency saturation pulse is applied at a frequency offset of 3.5 ppm relative to water to saturate the proton in the amide group. (C) The saturated proton in the amide group is exchanged with the unsaturated water protons. (D) A continuous exchange of saturated protons leads to a measurable decrease in signal from water.