Fig. 1.

R₁ measurements (logarithmic axis) for each of centres A–L. Each centre made measurements on five 2% agarose phantoms with different Ni²⁺ concentrations. The six horizontal lines represent R₁ values calculated from the field-dependent relaxivities as explained in Table 2. There are two groups of three data points for each phantom at each centre representing, respectively, days 1 and 2, and RoIs (X,Y,Z) = (0,0,0), (10,0,0) and (0,0,12). Error bars are T₁ fit errors from ParaVision.