Fig. 3.

Results from a simulation study of comparing EM and TwinMARM at 2 different sample sizes (n = 100, 400). The first row contains the results for ${\sigma }_a^2(v)$ as n = 100: Panel (A) is the ground truth image of ${\sigma }_a^2(v)$, in which five ROIs with black, blue, red, yellow, and white color represent ${\sigma }_a^2(v)=0,0.3,0.6,0.9\text{and}1.2$ , respectively. Panel (B) is a selected slice of ${\widehat{\sigma }}_a^2(v;h_{10})$ obtained from a simulated dataset by using the TwinMARM method. Panel (C) is a selected slice of ${\widehat{\sigma }}_a^2(v)$ obtained from the same dataset as panel (B) by using the voxel-wise EM method. Panel (D) is a selected slice of ${\widehat{\sigma }}_a^2(v)$ by using EM, after smoothing the same simulated data set as panel (B). The second row contains panels (E), (F) and (G) as n = 400, which are the corresponding results of panels of panels (B), (C) and (D), respectively.