Fig. 1.

Basics of the glycoNOE saturation transfer experiment. (A and B) Two possible NOE-based saturation transfer pathways from glycogen aliphatic protons to water: (A) saturation on glycogen aliphatic protons by a radio frequency (RF) pulse is transferred to a neighboring hydroxyl proton and subsequently to water via proton chemical exchange between glycogen hydroxyl protons and water; (B) saturation on aliphatic protons is transferred directly to a nearby bound water and then to the free water pool via water molecular exchange. (C and D) Schematic ¹H MR spectrum for glycogen in H₂O before (C) and after (D) the RF saturation of the aliphatic protons. S₀ and S represent water intensities in the two spectra. (E) Z-spectrum, showing S/S₀ as a function of RF irradiation frequency. Signal shown at around −1 ppm in the Z-spectrum is from glycogen aliphatic protons undergoing the possible NOE-based saturation transfer mechanisms (A and B), while signal at around +1 ppm is from hydroxyl protons undergoing chemical exchange with water (F). Because of multiple saturation transfer events in a single MR sequence, the glycogen signal in the Z-spectrum is enhanced compared to that in the ¹H MR spectrum. Note that the Z-spectrum is referenced to the water frequency.