the present invention is directed to radiolabeled n - substituted - 6 - iodo - 3 , 14 - dihydroxy - 4 , 5α - epoxymorphinans , intermediates for producing the same , and a process for the preparation and methods of detecting opioid receptors . the radioimaging agent of the present invention has the following formula : ## str1 ## wherein i is selected from the group consisting of 123 l and 125 ; and where r is alkyl , cycloalkylloweralkyl or allyl .