Magnetic resonance imaging of the Amine-Proton EXchange (APEX) dependent contrast

► Amine-water proton exchange (APEX) can be measured by a spin-locking technique. ► APEX is optimized with a relatively high power and short duration irradiation pulse. ► APEX contrast is sensitive to concentrations of protein and amino acids, and pH. ► In an MCAO model, APEX showed different patterns with ADC and APT maps. ► APEX signal can also be obtained with a CEST technique using similar parameters.