Chemical exchange saturation transfer MRI in the human brain at ultra-high fields

Chemical exchange saturation transfer (CEST) MRI can detect diluted molecules, i.e., metabolites and proteins, with enhanced sensitivity due to the exchange between their protons and the water protons. CEST benefits from ultra-high magnetic fields due to their improved spectral selectivity, which allows it to isolate more different metabolite peaks. However, UHF also leads to several challenges for CEST, such as field inhomogeneities and SAR limitations. Herein, before limits, methods, and applications are discussed, the basic CEST equations are reviewed to help understand the complex behavior of CEST labeling, linewidth, and concomitant saturation effects.