CEST

Chemical exchange saturation transfer imaging is a technique to indirectly measure pools of amide protons of low concentration. The key here is the amide protons must be physically exchanging with the bulk water. This method applies a saturation pulse at the resonance frequency of the amide protons for a period of time (e.g., 3 seconds) and then a standard water image is acquired. The change in signal intensity of the water image relative to a water image acquired with no saturation is related to the concentration and exchange rate of the amide proton pool (among a couple of other things).