Active groups are any of various pharmacologically or therapeutically active moieties, including {HEAD ~ moieties} useful for {TAIL ~ magnetic resonance contrast enhancement} 
useful for
Active groups are any of various pharmacologically or therapeutically active moieties , including { HEAD ~ moieties } useful for { TAIL ~ magnetic resonance contrast enhancement }
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD REL REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL