Fig. 5.

VDMP SI curves for 10% BSA in solution (a) and crosslinked (b) obtained using a VDMP-CEST sequence with eight Gaussian pulses and B₁ = 4 μT (200 Hz bandwidth). The solid lines are fits obtained using the two-pool Bloch equations assuming T_2s = 20 ms for BSA solution and T_2s = 0.13 ms for crosslinked BSA. Here T_2s for crosslinked BSA was determined by fitting the VDMP difference spectrum in Figure 6. The $T_{1\mathrm{w}}^{\ast }$ values were fitted to be 2 s (BSA solution) and 1.8 s (crosslinked BSA), respectively. The significantly lower $T_{1\mathrm{w}}^{\ast }$ relaxation times compared to PBS buffer are due to the back exchange of the fast exchange protons. c: Saturation power dependence for an 8-pulse VDMP-CEST difference SI (between t_mix = 110 ms and 0.7 ms) at offsets 3.6 ppm (APT) and −7 ppm (MTC background signal). The two solid lines are drawn for visual guidance only.