Joonas Arttu Autio1,2, Tao Jin3, S-G Kim3,4, Takayuki Obata1
1Department of Biophysics, National Institute of Radiological Sciences, Chiba, Japan; 2Department of Neurobiology, University of Kuopio, Kuopio, Finland; 3Department of Radiology, University of Pittsburgh, Pittsburgh, PA, United States; 4Department of Neurobiology, University of Pittsburgh, Pittsburgh, PA, United States
Previous study has demonstrated an indirect MRI detection of hydroxyl protons of small metabolites via chemical exchange saturation transfer. We used an on-resonance spin-locking (SL) pulse to detect proton exchange for hydroxyl-, amide- and amine-phantoms, and a protein sample. Analysis of spin-lattice relaxation rate in the rotating frame dispersion over a range of SL B1 fields, resulted in robust estimates for intermediate proton exchange rates and exchangeble proton site populations. Our results suggest that SL technique with on-resonance irradiation is not sensitive to very slow exchange, but may be more suited for quantitative study in the intermediate exchange regime.