PowerPoint Presentation - Activation Delays in FMRI: Estimation and Variability

7/2/2004 SSCC/NIMH 71

How many iterations ?

•Command line:

SurfSmooth -spec    ../SurfData/SUMA/DemoSubj_lh.spec     \
            -surf_A lh.smoothwm.asc                           \
            -met LB_FEM                                        \
            -input out_Del2.1D'[6]'                            \
            -Niter 100                                         \
            -fwhm 8                                            \
            -add_index                                         \
            -output out_Del2_smoothed.1D -talk_suma

-met : Specifies the smoothing method.

-Niter: number of iterations

-fwhm: Full Width Half Max of filter in surface coordinate units (usually mm) of an equivalent Gaussian filter had the surface been flat. With curved surfaces, the equation used to estimate FWHM is an approximation.

•The number of iterations controls the iteration step dt which must satisfy conditions that depend on the internodal distance and the spatial derivatives of the signals being filtered on the surface.

•As a rule of thumb, if increasing Niter does not alter the results then your choice is fine (smoothing has converged).