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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def _substract_hemispheres(active, reference, active_sigma, reference_sigma, voxel_spacing):
 """ Helper function for `_extract_hemispheric_difference`. Smoothes both images and then substracts the reference from the active image. """

    active_kernel = _create_structure_array(active_sigma, voxel_spacing)
    active_smoothed = gaussian_filter(active, sigma = active_kernel)

    reference_kernel = _create_structure_array(reference_sigma, voxel_spacing)
    reference_smoothed = gaussian_filter(reference, sigma = reference_kernel)

    return active_smoothed - reference_smoothed