I don't think Death is supposed to be in his head. I mean, there is definately a "living" entity called Death in the Marvel U. Sure, Thanos's Dad couldn't detect her in thanos Rising, but its Death, I would assume that she/it isn't detectable by anything if she/it doesn't want to be. It really wouldn't make sense for death to show up on scientific equipment, no matter how advanced.
Also, The last issue of X-Factor was good