UISNR ΞΆ(r β 0) at the sphere center as a function of sphere radius a with a fixed b = 35 cm for B0 = 1.5 T, 3 T, 7 T, 11 T, 14 T and 20 T, based on the analytic formula (solid lines) and full DGF simulations (data points). The dielectric properties were set to values in the average brain tissue. Dashed lines show the approximate dependence of UISNR on ~ aβ2.5, suggested by Kopanoglu et al for low field strengths. (15).