Water-metabolite Hydroxyl Proton Exchange Studied using Spin-Locking & Chemical Exchange Saturation Transfer Approaches

Tao Jin¹, Seong-Gi Kim¹

The chemical exchange saturation transfer (CEST) approach, based on the hydroxyl-water proton exchange, can provide valuable information on the concentration of glycogen, glycosaminoglycans, and myo-inositol, etc. Compared to the well-studied amide-water proton exchange for which a long and low- power irradiation pulse is generally adopted, the faster hydroxyl-water proton exchange suggests that a higher irradiation pulse power would be necessary to optimize the chemical exchange (CE) contrast. Unfortunately, given the smaller chemical shift between the hydroxyl and water protons, this would also lead to a larger direct water saturation effect. Recently, we reported that a similar CE contrast can be obtained with a frequency offset-dependent spin-locking (SL) approach which minimizes the contamination of the direct water saturation effect. In this work, we evaluated the hydroxyl-water CE contrast with the CEST and SL approaches