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In this section, we examine the characteristics of some of the
noise parameters in the model.
The middle (top to bottom) plots in
figure 8 show the first order temporal
autoregressive coefficient
obtained, where
is the mean of the marginal posterior of
. The temporal autocorrelation can be seen to be
spatially non-stationary. EPI slices are shown for comparison and
it can be seen that there is increased temporal correlation in
grey matter compared with white matter.
The bottom plots in
figure 8 show the average spatial autoregressive
coefficient
obtained, where
is the mean of
the marginal posterior of
. The spatial correlation
can also be seen to be spatially non-stationary, reconfirming the
finding of the DIC that a non-stationary spatial noise model is
required. It also indicates that, like the temporal
autocorrelation, the spatial autocorrelation is spatially
correlated with tissue type. There is also clearly increased
spatial correlation in grey matter compared with white matter.