My Husband Has Been Having Pain In His Upper Abdominal

my husband has been having pain in his upper abdominal region, he went to the dr. and had an Ultrasound done, they said they can not find anything, now they say he has to have an ENG. He said they told him this was a procedure where they take a camera down and look to see what is going on, when I looked it up, it makes no sense. Could you please let me know what exactly this procedure is called, cause, maybe my husband didn't hear it correctly. thank you.