Increased CEST specificity for amide and fast exchanging amine protons using exchange-dependent relaxation rate

It is challenging to remove overlapping chemical exchange saturation transfer (CEST) signals from nearby exchanging sites. Our previous study showed that the contributions of fast exchanging amines to CEST signals at 3 ppm induce a broad spectral region that overlaps with the amide proton transfer (APT) spectrum centered around 3.5 ppm. In this work, we apply an exchange-dependent relaxation rate (R_ex) for quantifying CEST effects to increased CEST specificity for amide and fast exchanging amine protons. Our results demonstrate that R_ex reduces the influences of overlapping CEST signals for APT imaging, and thus can significantly enhances the CEST detection specificity.