The CEST Effect of Guanidine and Hydroxyl Protons Can Be Used as a Positive Contrast in Ischemia

Tao Jin¹, Seong-Gi Kim¹

CEST imaging utilizing the the endogenous amide-proton transfer (APT) effect has shown great potential in stroke studies. However, the APT contrast in stroke is negative which decreases at the lesion region. A positive pH-sensitive imaging contrast would be preferable. In this preliminary study, we investigated the chemical exchange effects of endogenous guanidine and hydroxyl protons and their potential application in stroke studies. Because guanidine and hydroxyl protons exchange with water at much faster rate than amide protons, a positive chemical exchange imaging contrast induced by tissue acidosis can be detected by judicious selection of the off-resonance irradiation pulse power.