NIFTI
      NIFTI (*.nii and *nii.gz) is
      standard file format for volumetric data that is widely used in
      neuroimaging.  The original NIFTI-1 file format was based on
      16-bit signed integers and was limited to 32,767 in each
      dimension.  The NIFTI-2 format (http://www.nitric.org/forum/message.php?msg_id=3738)
      is based on 64-bit integers and can handle very large volumes and
      matrices.