How to bandpass filter an 4D image in Matlab?

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Sepp
Sepp 2015-8-1
编辑： Sepp 2015-8-1
Hello
I have implemented in Matlab a bandpass filter. The script is in the attachment.
I have now applied the filter to a 4D fMRI image. The first three dimensions are spatial, the last is temporal. The image is of size 80 x 35 x 12 x 350.
I have now made plots of the average time series before and after applying the bandpass filter.
Here is the plot after applying bandpass filtering:
As can be seen there are distortions at the beginning and end. Thus, from the result I had to throw away the first two and last two time points. The resulting images is thus of size 80 x 35 x 12 x 346.
Here is it after bandpass filtering and throwing away first and last two time points:
This one is before bandpass filtering:
Why is the shape of the curve exactly the same but just shifted on the y-axis? Did I made a mistake in my script?
By the way, I have used for the filter order n = 4. I don't know if it is right.

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