Abstract #4525

Study of Chemical Exchange Effect on Water MR Frequency Shifts using CEST

Xiang He¹, Jie Luo², Dmitriy A. Yablonskiy², Kyongtae Ty Bae¹

¹Department of Radiology, University of Pittsburgh, Pittsburgh, PA, United States; ²Mallinckrodt Institute of Radiology, Washington University in St Louis, St Louis, MO, United States

We investigated the effect of chemical exchange on water MR frequency through Bloch equation simulation and by in-vivo brain CEST experiment. Bloch equation simulation predicted a very small contribution from slow exchange amide (NH) group proton. The predicted contribution from faster exchange hydroxyl (OH) group, if measured with CEST approach, would also be small. Both statements were confirmed by in-vivo experiment, which found undetectable absolution frequency shift and little change on relative GM/WM frequency contrast by CEST. The effect by hydroxyl groups can only be detected by CEST if the phase evolution profile can be acquired with sub-millisecond echo time.