Following two-dimensional ARM, least-squares refinement and MC explorations was performed to generate Panel D. Intensities for each step were summed in a matrix of bins, each bin encompassing a small range of relaxation rate values around those labeling the bin. A contour plot of the results is given in Panel D. Note that one of the cross peaks is negative, a not uncommon finding in this laboratory. A more careful study involving models and simulations is necessary to fully interpret these results. The MC calculations did include variation of the offset and the equilibrium magnetization, as well as the flip angle (see discussion in Part 2). These parameters can contribute to marginalized uncertainties since they may vary from sample-to-sample due to experimental circumstances. They are not included in such plots because they offer no insight into the sample itself. For the two-dimensional data set, in contrast to the onedimensional measurement in Figure , fewer points were obtained, and a different sample was used under less optimal conditions, so only 3 non-zero rate components could be obtained.