pH is an important physiological index that alters in a host of disorders including inflammation, ischemic
stroke and cancer. Therefore, it is necessary to quickly and accurately detect pH in vivo for diagnosing tissue damage and
monitoring its response to treatment. Although magnetic resonance spectroscopy (MRS) can provide non-invasive measurement
of pH, its spatiotemporal resolution is somewhat limited, hindering its routine use in clinic. Recently, chemical
exchange saturation transfer (CEST) contrast mechanism has been developed as a novel approach to image pH at reasonable
spatiotemporal resolution with promising in vivo applications. In this review, we discuss the principles of CEST phenomenon,
quantify CEST effect and summarize its in vivo use.