Figure 6.

Demonstration of a 3-pool model of proton relaxation on R_1ρ dispersion and CEST contrast. This figure gives the simulated effects of multiple exchanging species and demonstrates the relative effects of slowly exchanging NH⁺ groups vs. typically faster ⁻OH groups at typical chemical shifts and exchange rates under physiologic conditions.

6.a. The individual and combined predicted contribution of exchange at different sites to R_1ρ dispersion from ⁻OH and NH⁺ sites at typical rates. This demonstrates that for a substance with an equal amount of peptide and sugar, the sugar dispersion contribution may dominate the overall R_1ρ dispersion curve, but by suitable selection of locking field, the relative peptide contribution can be modulated.

6.b. Calculated Exchange Rate Contrast (ERC) using Eq. 3.

6.c. & 6.d. CEST z-spectrum and MTR_asym for combined 3-pool model. Note how, unlike R_1ρ dispersion, the effects of each species may be separated by chemical shift.