Study of chemical exchange in the intermediate exchange regime: a comparison of spin-locking and CEST techniques
نویسندگان
چکیده
Introduction: Recently, an indirect MRI detection of hydroxyl protons of small metabolites via the water signal was reported [1]. Selective off-resonance irradiation attenuates the water signal via chemical exchange saturation transfer (CEST) between hydroxyl and water protons. It was found that the magnetisation transfer (MT) asymmetry ratio (MTRasym) depends nonlinearly on hydroxyl-group concentration. Since the spin-lattice relaxation rate in the rotating frame (R1ρ) is also known to be sensitive to proton exchange [2], we hypothetized that metabolite proton exchange may also be detectable using an on-resonance spin-locking pulse. The aim of this study was to quantify and analyze R1ρ dispersion over a range of spin-locking (SL) B1 fields (ω1,SL), for hydroxyl-, amideand aminephantoms, and a protein sample. The results were compared to measurements made with CEST off-resonance irradiation.
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Spin-locking versus chemical exchange saturation transfer MRI for investigating chemical exchange process between water and labile metabolite protons.
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