Is There Any Difference in Amide and NOE CEST Effects Between White and Gray Matter at 7T?

Measurement of Chemical Exchange Saturation Transfer (CEST) is providing tissue physiology dependent contrast, e.g. by looking at Amide and NOE (Nuclear Overhauser Enhancement) effects. CEST is unique in providing quantitative metabolite information at high imaging resolution. However, direct comparison of Amide and NOE effects between different tissues may result in wrong conclusions on the metabolite concentration due to the additional contributors to the observed CEST contrast, such as water content (WC) and water T relaxation (T). For instance, there are multiple contradictory reports in the literature on Amide and NOE effects in white matter (WM) and gray matter (GM) at 7T. This study shows that at 7T, tissue water T relaxation is a stronger contributor to CEST contrasts than WC. After water T correction, there was no difference in Amide effects between WM and GM, whereas WM/GM contrast was enhanced for NOE effects.