RF: Don't use nibabel Nifti1Image.get_fdata, as it causes RAM blow-out.
Store image data in its native type instead. Also use 64 bit when comparing arrays, as we can't remember why we decided 128 bit was needed (it probably isn't).
Store image data in its native type instead. Also use 64 bit when comparing arrays, as we can't remember why we decided 128 bit was needed (it probably isn't).