safe_load_4dpet_nifti
===========================================

.. py:function:: petpal.utils.image_io.safe_load_4dpet_nifti(filename: str) -> nibabel.nifti1.Nifti1Image

   Safely load a 4D PET NIfTI file.

   This function checks if the given file has a '.nii' or '.nii.gz' extension, then tries to load
   it as a NIfTI file using the nibabel library. If the file cannot be loaded, it raises an
   exception.

   :param filename: The path of the NIfTI file to be loaded.
   :type filename: str

   :returns: *Nifti1Image* -- The loaded NIfTI 4D PET image.

   :raises ValueError: If the file does not have a '.nii' or '.nii.gz' extension.
   :raises Exception: If an error occurred while loading the NIfTI file.