FIG. 1.

The experimental B_{avg power} (a) and B_{avg field} (b) that optimize the pulsed CEST contrast as a function of θ and duty cycle in the creatine/agar sample. Note that the optimal B_{avg power} is relatively independent of θ and duty cycle, while the optimal B_{avg field} is not. PTR is varied in order to find the optimal B_{avg power} and B_{avg field} at each θ and duty cycle. Similar results are found (but not shown) at pH = 6.0 at 9.4 T and pH = 6.4 at 4.7 T and in simulations of this creatine/agar sample and pseudo-phantoms with different frequency offsets (500 Hz to 3000 Hz), exchange rates (50 Hz to 250 Hz), and solute concentrations (0.001 to 0.005). The near independence of the optimal B_{avg power} on the other acquisition parameters makes B_{avg power} a more meaningful sequence metric than B_{avg field}. Figures (c) and (d) plot the CEST contrast as a function of B_{avg power} and B_{avg field}, respectively, at θ = 180°. Note the similar dependence on B_{avg power} at all duty cycles.