in recent years, several radiopharmaceuticals have been developed for imaging regional cerebral blood flow (rcbf) such as 75se labelled pipse and mose, ²º¹ti labelled ddc and 99mtc labelled hmpao. hmpao with two asymmetric carbon atoms (at the 3 and 9 positions), produces d,1 and meso isomers, only one of which is retained in the brain. rapid intracellular conversion of 99mtc-d,1-hmpao to hydro...