Dear Haniyeh,
if you want to extract raw or filtered data from a certain location for further time series analysis, you may want to try the "Util->Volume of Interest" tool. This tool lets you define various shapes of ROIs and extracts data for them. It doesn't save the ROI as a 3D image file, though. If you need this ROI image, you may want to try the Volumes toolbox available from the SPM extension web page. "Tools->Multiple Volumes->Create and apply Masks" lets you define ROIs and allows to save them as images. However, you should be aware that with both tools your desired sphere might actually look more like a bunch of voxels, if the radius of the sphere is not very large compared to the voxel size of your images.
Best regards,
Volkmar
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