Amide proton chemical exchange saturation transfer at 9.4 T

The backbone amide groups in peptides and proteins [1] are one of many endogenous compounds able to exhibit a chemical exchange saturation transfer (CEST) effect by exchanging protons with water molecules. The resonance frequency of the amide protons is situated at 3.6 ppm from the water resonance frequency. Unfortunately, the quantification of the amide proton transfer (APT) effect using a standard asymmetry analysis approach is hindered by the nuclear Overhauser effect (NOE) at upfield frequencies (e.g. -3.6 ppm). Very recently [2] it has been shown that in rat brain the APT effect and the NOE can be directly discriminated at ultrahigh magnetic field due to the concomitant wide spectral separation. In this initial work we demonstrate that it is possible to acquire amide proton CEST spectra in the human brain at 9.4 T