Cluster Probability fMRI Smoothness

This plot shows the measured and theoretical smoothness of an fMRI data set after low pass filtering. As shown in the plot, the measured smoothness within the brain region varies about the theoretical value.

The measured smoothness is numerically estimated as the determinate of the variance-covariance matrix of the difference images of temporally adjacent image slices. See equation 6 in Xiong

The theoretical value of 0.47 is based on a Gaussian LPF with an image space FWHM = 1.76 pixels (N = 64, K space radius = 16). See equation 8 in the implementation details.

Data from Wei Chen (I_MF_CB_8Hz_TR_2s.fid).

Jinhu Xiong, et al. ``Clustered Pixels Analysis for Functional MRI Activation Studies of the Human Brain'' Human Brain Mapping, 3:287-301(1995).