We use one of the EPI scans to generate the USAN and set the brightness threshold conservatively, so that only the voxels that we can be confident are of the same matter type are used. The data is motion corrected and non-linear high pass filtered. Results for both data sets are shown below. The local autocorrelation estimation technique is shown to give good localised estimates. Other results indicate that the accuracy of the estimation makes it unnecessary to use low pass filtering to precolour the noise.
Further work includes using the autocorrelation estimate to prewhiten the data.
References 1 S M Smith and J M Brady. 2 F.T. Wright T. Robertson and R.L. Dykstra. Order Restricted Statistical Inference. K.J. Worsley and K.J. Friston. Analysis of fMRI time series revisited - again.