Dear All,
I have another problem about filtering with 3dFourier. Hope someone can help me.
I bandpass (0.01Hz - 0.08Hz) filtered the fMRI data with 3dFourier:
3dFourier -prefix BPnor008 -lowpass 0.08 -highpass 0.01 -ignore 1 -retrend nor008_FL+orig.
I found there existed a linear trend in the time series of some voxels. However, it seems no linear trend exists in the original time series of the same voxels.
Although I used the option "-retrend", I think no linear trend should exists in the filtered time series if no linear trend in the original time series. Am I right?
Strangely, the linear trend disappeared if I only lowpass filtered the time series:
3dFourier -prefix LPnor008 -lowpass 0.08 -ignore 1 -retrend nor008_FL+orig.
The first, second and third attached images are the original time series, the bandpass(0.01Hz - 0.08Hz) filtered time series, and the lowpass(<0.08Hz) filtered time series, respectively.
Thanks!
Meng
